SEWAGE SLUDGE Published by the McGraw-Hill Book. Company .New Voirk, NSucce.s.s6ns to the BooltDepartments of the McGraw Publishing Company Hill Publishing Company Publishers of Books for Electrical World The Engineering and Mining Journal Engineering Record American Machinist Electric Railway Journal Coal Age Metallurgical and Chemical Engineering r J r ."J Ti SEWAGE SLUDGE TREATMENT AND UTILIZATION OF SLUDGE BY ALEXANDER ELSNER THE DRYING OF SLUDGE FR. SPILLNER TRANSLATED BY KENNETH AND ROSE S. ALLEN OPERATION OF MECHANICAL SEWAGE PLANTS BY FR. SPILLNER AND MR. BLUNK TRANSLATED BY EMIL KUICHLING, M. AM. SOC. C. E. CONSULTING ENGINEER SLUDGE TREATMENT IN THE UNITED STATES KENNETH ALLEN, M. AM. SOC. C. E. ENGINEER METROPOLITAN SEWERAGE COMMISSION OF NEW YORK McGRAW-HILL BOOK COMPANY 239 WEST 39TH STREET, NEW YORK 6 BOUVERIE STREET, LONDON, E. C. 1912 : A, -$? COPYRIGHT, 1912 BY BOOK COMPANY Printed and Electrotyped by The Maple Press York, Pa. PREFACE With the rapidly increasing number of sewage treatment plants in the United States and the development of new methods, those interested in the subject will appreciate the valuable contribution to our literature on the troublesome subject of sludge contained in the following monographs by Dr. Eisner, Dr. Spillner and Mr. Blunk. The painstaking experiments and extended observations of these gentlemen, carried on under most favorable circumstances, enable them to speak with exceptional authority on this subject. Dr. Eisner's paper "Die Behandlung und Verwertung von Klarschamm" 1 contains a large fund of data gleaned from experience with, and observation of, the more important German plants arid those of England. The broad scope and thorough treatment are characteristic of the German investigator. Dr. Spillner's paper, entitled "Die Trochnung des Klar- schammes," 2 is particularly valuable on account of the details of the results accomplished up to the end of 1909 in the operation of the plants of the Emschergenossenschaft, which are now receiving so much attention in this country. Dr. Spillner, as chemist, gives this information at first hand. The third paper comprises Part III of a series written yet more recently by Dr. Spillner and Mr. Blunk on "Results of the Opera- tion of Some of the Mechanical Sewage Clarification Plants of the Emscher Association/' 3 This has been translated by Mr. Emil Kuichling, M. Am. Soc. C. E. The title of this paper is, "Examination of the Sludge, the Liquid in the Septic or Lower Chamber of the Deep Emscher Tanks, and the Water Drained from the Wet Sludge on the Drying Beds." As this of more recent date than the former article by Dr. Spillner the authors have had the advantage of further experience in the operation of tanks of the Emscher or Imhoff type, as well as of the comments and criticisms concerning their design or efficiency that have 1 Fortschritte der Ingenieururissenschaften, Zweite Gruppe, 24 Heft, Leipzig, 1910. 2 Mitteilungen aus der Koniglichen Prufungsanstalt fur Wasserversorgung und Abwasser- beseitigung, 14 Heft, Berlin, 1911. 3 Technisches Gemeindeblatt, Vol. XIII, pp. 313-377 241314 vi PREFACE been brought out in the intervening time. Moreover, Mr. Blunk, as operating engineer, adds to the discussion informa- tion derived from the engineer's point of view concerning their operation. Although up to the present time sludge treatment has been accorded little attention in America as compared with Germany or England, this will be demanded more and more hereafter. Some really creditable work has been done in this direction, how- ever, and it has therefore been thought desirable to add some notes on the characteristics of American sewages and on the more important results reached here in the treatment and utilization of sludge. For the greater convenience of American engineers the meas- ures given, unless otherwise stated, are those customarily employed in the United States: the gallon being the United States gallon of 231 cu. in.; the ton, that of 2000 Ibs., etc.; but for the convenience of others the metric measure given by the authors of the first three parts are also stated. Acknowledgment is here made of the courtesy of the city officials and others who have furnished data concerning the works under their charge and, in particular, of the valuable assistance rendered by Mr. Emil Kuichling in the translation of obscure passages in the original papers by Drs. Ing. Eisner and Spillner. K. A. NEW YORK, November 26, 1911 CONTENTS PART I TREATMENT AND UTILIZATION OF SLUDGE. BY ALEXANDER ELSNER. PAGK Treatment and utilization of sludge 3 I. Introduction 3 II. Sludge, its composition and amount 7 Detritus from grit chambers 8 Detritus from screening plants 9 Sludge from plain sedimentation 9 Grease contained in sludge 10 Sludge from chemical precipitation 10 Sludge from lignite process 11 Sludge from septic tanks 11 Digestion of sludge 11 Sludge from contact beds 12 Sludge on irrigation fields 12 Influence of the manner of treatment 13 Amount of sludge 15 III. The removal of sludge from clarification tanks 22 Removal of detritus from grit chambers 25 Removal of sludge from tanks, wells and towers 27 a. Removal with interruption of operation 27 b. Removal of sludge during operation 35 1. Construction . 35 2. Mechanical contrivances for removing sludge during operation 44 c. Contrivances and conduits for conveying sludge . . 50 IV. Reduction of the water in sludge 54 a. Drying in the air 56 b. Drying by filter presses 64 c. De- watering sludge by centrifugal machines 69 d. Other methods of reducing the water in sludge 77 V. Utilization of sludge . . ' 81 ' a. Utilization of the fertilizing properties of sludge .... 83 1 . The use of wet sludge as a fertilizer 85 2. Utilization of de- watered sludge as fertilizer ... 91 3. Production of fertilizer which can be strewn over the ground 93 b. Complete utilization of calorific value by burning .... 95 c. Production of gas 101 ix x CONTENTS PAGE d. Extraction of grease 106 e. Various other methods of disposal 109 VI. Considerations regarding the treatment and utilization of sludge in the choice of a method of clarification Ill Concluding remarks 116 PART II THE DRYING OF SLUDGE. A REPORT FROM THE SEWERAGE DIVISION OF THE EMSCHER ASSOCIATION. KGL. BAURAT MIDDELDORF, CHIEF ENGINEER, DR. ING. IMHOFF, DIVISION SUPERINTENDENT. BY DR. ING. FR. SPILLNER. ESSEN-RUHR. Introduction 121 I. The drying of sludge 123 Necessity of drying 123 Methods of drying different kinds of sludge 130 II. Drying of fresh sludge . 131 III. Drying of septic tank sludge 140 IV. Drying of Emscher tank sludge 143 Experiments with draining 146 Comparative experiments with fresh and decpmposed sludge. 152 The reasons for facility of drainage 159 Experience with drainage methods in large plants ..... 164 PART III RESULTS OF THE OPERATION OF SOME OF THE MECHANICAL SEWAGE CLARIFICATION PLANTS OF THE EMSCHER ASSOCIATION. BY DR. ING. F. SPILLNER AND MR. BLUNK. Introductory note . . . . : 172 Measurements of the sludge 173 Examination of the liquid sludge .178 Examination of the drained sludge 184 Examination of the liquid drawn from the septic chamber of an Emscher tank and the drainage water from the sludge beds . . . .186 Yearly costs 189 PART IV SLUDGE TREATMENT IN THE UNITED STATES. BY KENNETH ALLEN, M. AM. Soc. C. E. I. American sewage 195 II. Detritus from grit chambers 199 III. Screenings 202 IV. Sludge from plain sedimentation 210 V. Septic tank sludge 217 VI. Sludge from Emscher tanks 224 CONTENTS xi PAGE VII. Sludge from chemical precipitation 230 VIII. The disposal and utilization of sludge . 236 1. Disposal of night soil on farms . 236 2. Dumping at sea 3. Application to the land . 239 4. Filter-pressing 5. Drying with centrifugal machines . 244 6. Recovery of colorific value . 246 IX. Summary and conclusions 252 TREATMENT AND UTILIZATION OF SLUDGE BY ALEXANDER ELSNER TRANSLATED BY KENNETH AND ROSE S. ALLEN PREFACE The following treatise deals with the problem of treating and utilizing sludge. It seems an opportune time to present this, for although there has been great activity during the past few years in solving the question of sludge disposal, yet a general discussion of the require- ments necessary for its treatment and utilization and their realization by existing methods has not yet been published. In many cases the question of treating and utilizing the sludge, even in thoroughly worked out projects, has been left open. This work may be of assistance to engineers who are designing such plants in judging and deciding these matters. It is based on personal observation in journeys of inspection, in which a large number of important plants for treating sludge were examined, also upon a study of the most recent literature, a list of which is appended, and on information which has been placed at my disposal by a great number of city officials, for which many thanks are due. ALEXANDER ELSNER. DRESDEN, March, 1910. VI 1 TREATMENT AND UTILIZATION OF SLUDGE CHAPTER I INTRODUCTION The satisfaction felt in the more perfect methods of sewage clarification and their adaptation to different kinds of sewage has been diminished to an increasing extent by the question of the disposition of the sludge which accumulates in the vicinity of the works. In 1857 the highest sanitary authority of England proposed that a part of the filth in sewage be removed before discharge into streams in order to prevent their further pollution and the intolerably unsanitary conditions resulting therefrom; and it was then that the sludge question first arose, i.e., the question of its removal and the disposal of the filth separated from the liquid. Formerly sewage had been disposed of in the easiest and cheapest way by discharging it into a stream, or, in a few in- stances, distributing it over the land for financial gain, while now the sludge was accumulated in the neighborhood of the plant without considering that the gain in sanitary conditions was more than offset by the putrefying masses of sludge in the thickly settled manufacturing towns, thereby impairing the health of the inhabitants. The farmers did not make use of the sludge as had been expected. This was partly because they discovered that its value had been overestimated, and partly because of an increase in manufactures, whereby they were driven more and more to truck farming in those populous districts, requiring a more expensive fertilizer, which they were then able to pay for. Two ways have been attempted to reduce this nuisance. A method was sought to make the sludge, which contained much lime after the prevailing chemical treatment, transportable by draining off a part of the water before putrefaction set in, in 3 4 SEWAGE SLUDGE order that its use might not be confined to the limited number of farmers in the neighborhood of the works, and so that, in this more portable condition, it might have an increased value commercially. Clarification processes were sought which would promise a smaller output of sludge while otherwise equally efficient. The rapid spread of septic treatment may be attributed to an exaggerated idea of the reduction of sludge which was antici- pated. A further advantage .was the comparative infrequency of the objectionable process of cleaning required by this method. The introduction of biological methods, which seemed at once to solve the difficulty by means of the sludge-consuming activity of micro-organisms, was favored by the difficulty in caring for the annually increasing quantities of sludge due to chemical precipitation. The assumption that the amount of sludge would be reduced by 70 per cent, or even 90 per cent., as had at first been expected, in septic tanks, was shown to be erroneous, nor was the difficulty of caring for the sludge removed by biological treatment; for even contact beds become clogged more or less quickly, according to the fineness of the material and the frequency of filling, and must then be taken apart so that the sludge can be washed away. With sprinkling filters, especially when made of coarse material, the necessity for taking them apart does not occur so frequently, but flakes of deposited matter are washed out of the beds, which usually necessitates the placing of a sedimentation basin in the line of the effluent conduit. It has been found that the greatest practicable preparatory clarification by sedimentation tanks may increase the cleansing power of bacteria beds by 1 1/2 or 2 times, while at the same time postponing a premature accumu- lation of sludge. This is also true of sprinkling filters and intermittent land filters. Here it is especially the grease, animal fibers, hair and cellulose which form a felt-like surface sometimes 2 in. (5 cm.) thick, injuring the plant life, lessening the filtering capacity, and hindering the aeration of the soil. Removing this cover is expensive and much of the fertile soil is lost. Furthermore, much larger volumes of sewage can be delivered to the land after thorough preliminary treatment (English estimates give 5 times as much with chemical treatment, 10 times as much with biolog- ical treatment), a most important fact in consideration of the TREATMENT AND UTILIZATION OF SLUDGE 5 oasinii 1 area of available land and its increasing value accom- panying the growth of cities. It is not only in sedimentation, septic treatment and chemical precipitation, as well as in screen- ing plants and grit chambers where sludge naturally accumulates, but also in sprinkling niters, land filters and contact beds that it becomes a troublesome factor. Two qualities render sludge particularly troublesome to both the technical employees and to those living near the plant, and also, on account of the high cost of removal, to the town author- ities. These are the tendency to putrefaction, particularly in warm weather, and the contained water, which increases its volume and adds to the cost of transportation. In particular its tendency to putrefy quickly in warm weather with a strong, disagreeable odor, which becomes a nuisance not only to the operatives at the works themselves, but also to the residents of the neighborhood, made a change ever more impera- tive. This is easily understood when one remembers that by far the greatest part of a city's filth is stored near the clarification plants. What large quantities are involved may be seen from the fact that in the 16 years from 1887 to 1903, 930,000 cu. yds. (711,000 cbm.) of solids were removed from the sewage of Frankfort. Here, indeed, as in most places, a further accumula- tion of sludge might be avoided by its use as a fertilizer; but the annoying odors already mentioned cannot thus be avoided since the great proportion of water calls first for its drying out in the air. Commonly, however, the demand for fertilizer is not great since, especially as in the vicinity of towns lacking a sewerage system, the supply of night-soil, with its higher fertilizing power, may supply the farmers' needs. Many examples made it clear that in planning clarification plants the greatest attention should be given to the disposal of the sludge. This was the case, not only in England, where the sludge nuisance appeared more pressing on account of the chemical treatment, which was pre- ferred for its greater removal of sludge and for the enhanced value of the sludge itself due to the addition of lime, but also in Germany, where, decades later, similar conditions were repro- duced on a smaller scale. But even where it is easy to dispose of the sludge, whether dried or wet, there is occasion for further treatment. For, as this by-product is of small value and of considerable mass, there should be an effort to avoid its transportation and treatment, 6 SEWAGE SLUDGE especially by manual labor, which increases the cost to an un- necessary extent. What an enormous expense may result is seen in London, where about $238,000 (1,000,000 M.) is annually spent in carrying the sludge to sea in tank steamers. In Leipzig, too, the annual expense of handling is about $7100 (30,000 M.), mainly for carting off the dried sludge. Efforts to improve this condition have been made in two directions. One was to remove the sludge and to simplify and cheapen its transportation to drying beds or places of utilization, and in particular to avoid the unhygienic manual labor. One way to effect this is to give the tanks, wells and towers for sludge the best possible form; and, further, to install machinery and apparatus for the automatic removal of the sludge, or to operate the plant so as to produce the least possible amount of sludge with equal clarification. Other experiments and attempts have been made to remove the water from the sludge more quickly and with less objection than by drying in the open air, or at least to improve upon this method, water being the greatest drawback to rendering sludge of value. Above all, it is desirable to retain the fertilizing prop- erties of the sludge, its fats and calorific value, and in this way to reduce the cost of treatment, efforts which are important even from the agricultural standpoint. It is estimated that $143,000,000 (600,000,000 M.) are annually lost by failure to utilize the nitrogen in sewage, but one-tenth of which is used. Although these figures are theoretical and perhaps exaggerated, they should cause one to reflect. These considerations for simplifying and improving sfudge disposal and utilizing it, or at least attempting to do so, are of great importance to an engineer who is planning a disposal plant. Disregard of these matters has often resulted in costly alterations, or even a complete change of plan. Any standardizing of sewage treatment should be strictly avoided and each plant designed with reference to the particular local conditions. CHAPTER II SLUDGE. ITS COMPOSITION AND AMOUNT By sludge is here meant all the residue which remains after treatment of city sewage by grit chambers, bar screens and mesh screens, tanks, wells, and towers, by plain sedimentation or chemical precipitation, septic tanks, contact beds or irrigation fields. Its composition and amount depend upon: 1. The composition and volume of the sewage. 2. The manner of collection. 3. The method of treatment. 4. The operation of the plant. 1. The amount and composition of sludge, which consists mainly of the undissolved matter contained in the sewage, vary quite as much as the character of the sewage in different towns. Even the amount differs very greatly. To mention but two examples, Paris sewage contains 1515 parts per million (mg. per liter) of undissolved material, but that of Hanover 270 parts per million (mg. per liter). Those cities whose inhabitants have low standards of living and use but little water per capita, have a very concentrated sewage, and so, in general, a large volume of sludge. Aside from this, the amount of trade wastes determines to a large extent the character of the sewage. This depends, not only upon the volume of the trade wastes, which sometimes surpasses that from domestic sources, but also upon. the addition of certain substances, particularly free acids and salts of iron, which can convert undissolved into soluble material, and thus effect the amount and character of the sludge. Certain industries add substances which increase the putrescibility of the sludge or retard its drying, such as textile mills which give it a fibrous, felt-like character. Others add large quantities of grease which may determine the method of removal or treatment of the sludge. Other substances, particularly from metal works, act on the sewage and sludge as a disinfectant. 7 8 SEWAGE SLUDGE The daily change in the character of the sewage is of import- ance in plants where the sludge is removed during continuous sedimentation, particularly where it is carried immediately to the filter press for further treatment. Not only is its character changed but also its volume. 2. The system of sewerage is of importance in so far as the amount and character of the sludge is concerned, as considerably more mineral matter reaches the sewers in a combined system. The amount of this material again effects the character of the sludge, particularly its percentage of moisture. Large quantities of filth are washed in from the streets during heavy rains as also by the cleaning of asphalt and wooden pavements. In towns where the streets are chiefly macadam and where no catch basins are provided, in order to collect as much of the filth as possible at one point outside the city, especial care should be taken, in planning the dimensions of the grit chamber and the means for cleaning it, on account of the large amount of mineral matter brought down. If the sewage passes through pumping stations and long force mains or traverses long distances before it reaches the treatment plant, much of the suspended matter will be broken up, thus reducing the amount retained by the tanks and screens, a con- sideration of especial importance where the clarification is effected by these means only. 3. The greatest variation in the volume and character of the sludge is due to the method of clarification: that is, the method and arrangements by which the separable matter is removed from the sewage. Not only is the amount of the sludge, but also its condition and composition, dependent on the efficiency of the process of clarification. DETRITUS FROM GRIT CHAMBERS The sediment removed by grit chambers is composed princi- pally of inorganic matter. Its putrescibility, the most offensive quality of sludge, is therefore slight, as well as the amount of water contained. This varies from 35 to 60 per cent. It depends, aside from the manner of cleaning the grit chamber and the fre- quent stirring-up resulting therefrom, upon its content of organic matter, and this, again, upon the velocity of flow provided. Two TREATMENT AND UTILIZATION OF SLUDGE 9 inches (5 cm.) per second should be the least. On the one hand the attempt should be made to keep the deposit as free as possible from putrescible organic matter in order to permit of its con- venient disposal, its handling and transportation; on the other, it should be remembered that the mineral particles of the de- tritus carried to other parts of the 'plant form there an undesir- able ballast which makes the care and utilization of the accumu- lated sludge difficult. For this reason the installation of a special grit chamber is seldom omitted. DETRITUS FROM SCREENING PLANTS The screenings from screening plants differ greatly both in amount and character. The meshes of the screen or the spacing of the bars may run from 1.0 in. (25 mm.) to 0.04 in. (1 mm.) according to whether it is desired to keep coarse matter from the sewage or sludge pump, or to secure the greatest possible clarification of the sewage. The amount changes, also in the course of the day. As most of the coarser suspended matter consists of wastes from habita- tions the amount reaches its maximum at noon or soon after, and almost disappears by nightfall. ( This fact is of importance in the case of .bar screens. The material is almost wholly organic and consists of scraps of meat, vegetables or fruit, cloth, hair, corks, wood and lumps of fecal matter. Its composition varies so widely that it is impossible to give an average value. The amount of water contained is small, amounting to but 70 or 80 per cent. On account of its organic origin it is highly putrescible. SLUDGE FROM PLAIN SEDIMENTATION Sludge formed by the process of sedimentation in tanks, well and towers consists of a semi-liquid, black mass which soon be- comes offensive with much gas and foul odors. Its decomposi- tion is accelerated by warm weather. The amount of water in the sludge in tanks is usually 90 per cent., in wells and towers 95 per cent, and more, and is regulated by the manner of treatment. In conjunction with the sludge from chemical precipitation and septic tanks, it produces the largest volume to be treated on account of the proportion of water contained. Therefore, 10 SEWAGE SLUDGE most of the efforts and treatment for the utilization of sludge aim at its removal. GREASE CONTAINED IN SLUDGE Here we see the significance of the grease contained in sewage and also in the sludge as, on the one hand, this may interfere with the use of the sludge in agriculture and, on the other, has led to attempts for the recovery and utilization of the grease. According to the experiments of Schreiber, the Berlin sewage contains 22 Ibs. of grease per 1000 persons (20 g. per capita) per day, i.e., 16.1 Ibs. (7.3 kg.) per capita per annum. This corresponds to a quantity of grease in the sewage of from 0.01 to 0.026 per cent., most of which reappears in the sludge. Also, in the settled sludge of other cities, as Frankfort-on-the- Main, Mannheim, Elberfeld and Cassel, the amount of grease is found to be from 15 to 20 per cent, of the dried material. The Kremer apparatus shows much larger amounts of grease in the scum. In the Osdorf experimental plant, with an amount of water in the sludge from 81 to 86 per cent., they found from 9 to 6 per cent, of grease, or, referred to the dried material, as much as 49 per cent. In Charlottenburg, with the same appara- tus, 12.8 Ibs. of grease per cubic yard (7583 g. per cbm.) was recovered. This would give 500 Ibs. (227 kg.) of grease from 7,925,000 gallons (30,000 cbm.) of sewage per day for the whole city. SLUDGE FROM CHEMICAL PRECIPITATION The sludge from chemical precipitation is similar in character to that from plain sedimentation but the quantity is much larger, which fact, taken in connection with its decreased value as a fertilizer on account of chemicals used in the process, has been to a great extent the reason for abandoning this method of treatment. The large volume of sludge is explained by the more complete separation of the undissolved material by chemical treatment, and also by the addition of the precipitant. It should be noted that 2086 Ibs. of lime per million gallons (250 g. per cbm.) of sewage, which is often used in England, produces not only 0.55 Ibs. (250 g.) of sludge but 5.52 Ibs. (2500 g.) as ,the lime settles as sludge containing about 90 per- cent, water. TREATMENT AND UTILIZATION OF SLUDGE 11 SLUDGE FROM LIGNITE PROCESS The sludge obtained by this process is very full of water (95 per cent, or more) but can generally be easily pressed or dried in the air, as is done at Copenick, without putrefaction or the emission of unpleasant odors. The pressed sludge has but a faint musty smell and is non-putrescible. SLUDGE FROM SEPTIC TANKS The same thing is true of the sludge from the septic tank, as this has gone through the process of decomposition in the tank. This, too, has only a slight musty odor. It has a granular earthy structure from decomposition, in contrast with precipitated sludge which, after the water is drawn off, has a fibrous, felt-like appearance. The earthy character of sludge from the septic tank process aids in the removal of the water, enabling it to dry more rapidly. It is also more fluid, in comparison, in spite of the small amount of contained water about 80 per cent. All the data thus far given concerning the amount of water contained in sludge are averages taken from a large number of plants and are subject to certain variations depending upon the design of the plant and particularly upon the thoroughness of the mode of operation and the method of removing the sludge. ' DIGESTION OF SLUDGE In the septic process one phenomenon has been much discussed, namely, the digestion of the sludge. That is to say, a diminution of the quantity of the sludge in such a manner that the dried solids contained both in it and in the effluent of the septic tank are less than the amount received. A reduction of 80 per cent, or more was anticipated by the introduction of the septic treatment and thereby relief from the troubles associated with sludge. The amount of suspended matter contained in the effluent must be considered in determining the percentage of reduction, and this is rather large. In different English cities, for example, it varies from about 35 parts per million (mg. per 1.) at Salford to 244 parts per million (mg. per 1.) at Birmingham. Moreover, the sludge becomes more dense in time and in this way loses a part of its water. In fresh sludge this is about 90 per cent, and in dried sludge 80 per cent., as has been noted; therefore the former has twice the volume of the latter. 12 SEWAGE SLUDGE Moreover, a part of the solids is transformed into gas and another part liquefies. This alone is to be considered in the reduction of sludge. The amount of this in different English cities is as follows: Birmingham 10 per cent., Manchester 25 per cent., Leeds 30 per cent., Sheffield 33 per cent. In Unna, also, where it was removed only once a year it was found to be but about 60 per cent, of the aggregate amount when removed weekly. The reason for the difference between these several figures lies partly in the difference in the composition of the sewage, es- pecially whether it is putrescible domestic sewage or whether it contains much impalpable mineral or other material not easily broken up, and partly in the different amounts of the solids con- tained in the effluent of the septic tank. A certain amount of sludge reduction may always be expected after prolonged storage. SLUDGE FROM CONTACT BEDS Sludge is also found in contact beds and its removal at stated intervals is necessary, depending on the extent of its preparatory treatment, the construction of the beds and their operation. The sludge that is washed out is of an earthy consistency, con- tains 60 to 75 per cent, water and is readily dried. As it is bio- logically digested it does not become foul later except in those cases where the beds are overloaded. It strongly resembles septic sludge. In sprinkling filters it contains, under certain conditions, a larger amount of organic matter, such as the larvae of flies and mosquitoes, while in contact beds it contains earth- worms and other worms. SLUDGE ON IRRIGATION FIELDS Sludge sometimes appears on irrigation fields in the form of a layer of slime which covers the soil. It consists of cellulose and grease, prevents the admission of air and sewage and must be removed with a spade. This slime can be avoided by installing sedimentation tanks. The differences in sludge obtained by the various kinds of treatments mentioned correspond also to its chemical composi- tion, so that there is little practical value in giving definite limits to the amount of each ingredient of which it is composed. TREATMENT AND UTILIZATION OF SLUDGE 13 In order to present a general idea of the matter some analyses showing results obtained with different methods of treatment are here given. Later some materials will be considered more fully which give to sludge a certain fertilizing value. ANALYSES OF SLUDGE IN PER CENT. Sludge from Sludge precipitated by plain sedimen- tation Sludge Septic from Frankfort-on- Main Lime Sulphate of iron and lime Sludge. Stuttgart contact beds. Tempel- hof Wet Dry Frankfort-on-Main Water 91.07 90.85 80.96 77.3 74.2 Organic matter 5.08 57.00 4.15 13.31 7.35 16.5 Nitrogen contained . 0.23 2.85 0.31 0.10 0.4 0.6 Inorganic matter 3.85 43.00 5.00 5.73 15.35 9.3 Phosphoric acid con-: 0.23 2.85 0.07 0.02 0.4 0.5 tained. Potash : 0.05 0.56 0.02 0.007 0.1 Oxide of iron 2.0 INFLUENCE OF THE MANNER OF TREATMENT 4. The management of the plant has a marked effect on the quality of the sludge, especially the amount of water contained, and therefore upon the total volume. As already shown, this is the case to a certain extent with grit chambers. A frequent cleaning out of the sludge, possibly with dredges, causes a stirring up of the deposit, thus mixing it with the sewage, while in plants where the cleaning is done at longer intervals after cutting out the grit chamber, which is ordinarily divided into compartments built side by side, the grit deposits more firmly and contains less water. This difference is not very important in consideration of the comparatively small quantity of deposit in the grit chamber, its easy handling and its inoffensive character. In settled sludge, on the other hand, the quantity of water is of great importance, as its large amount may readily result in a nuisance on account of its unforeseen increase as well as from the greater cost of the transport and disposal of the increased volume. In considering the influence of the contained water on the amount of sludge it should be noted that 1.3 cu. yds. (1 cbm.) of sludge having 80 per cent, moisture contains 7 cu. ft. (200 1.) of 14 SEWAGE SLUDGE dried solids, while 1.3 cu. yds. (1 cbm.) of sludge having 95 per cent, moisture contains 1.75 cu. ft. (50 1.) of dried solids; there- fore the amount of the contained solids is as 4 :1 . A given volume of sewage from which the suspended matter is removed and dried produces in the first case 4 times that in the last. The amount of this material alone corresponds to the degree of clarification, but not to the total volume of the sludge. Sludge contains the most moisture, 95 per cent, and over, in plants where it is removed continuously, as in this case it is always kept in motion and cannot settle. In clean sedimentation tanks also, i.e., where great care is taken to prevent the settled sludge from putrefying, the water content is large, especially in summer, as the sludge must be removed frequently. In order to reduce the volume of sludge it may be allowed to remain longer and partially digest when the effluent from the sedimentation tank is given subsequent treatment, possibly on contact beds of irrigation fields. Sludge is then produced with 85 to 90 per cent, less moisture. It is assumed that the sewage does not contain substances from industrial plants which inhibit putrefaction, so that it is at most a question of reducing the volume by consolidation from prolonged settling. That the consolidation of sludge has an effect on its water con- tent is seen in the Emscher tank, where the sludge at a depth of 36 ft. (11 m.) contains 70 per cent, moisture and at 29.5 ft. (9m.) 75 to 80 per cent. This occurs less in ordinary tanks, with their less depth of sewage and sludge, than in wells and towers. The velocity of the sewage also affects the amount of water in the sludge. This has been demonstrated by the experiments of Steurnagel at Cologne. It was found that the slower the velocity in the tank the greater the volume of sludge. The experiments showed that in 264,170 gallons (1000 cbm.) of sewage with a velocity of 0.156 in. (4 mm.) per second the result was 5.28 cu. yds. (4.04 cbm.) of sludge, with 95.57 per cent, of moisture and 4.43 per cent, of dry material; with .78 in. (20 mm.) per second velocity, 3.23 cu. yds. (2.47 cbm.) of sludge, with 92.87 per cent, of moisture and 7.13 per cent, of dry material; with 1.56 in. (40mm.) per second velocity, 2.41 cu. yds. (1.84 cbm.) of sludge, with 91.34 per cent, of moisture and 8.66 per cent, of dry material. An examination of these figures shows that the TREATMENT AND UTILIZATION OF SLUDGE 15 volume of sludge is greatly increased by diminishing the velocity, but that the amount of the dried material is less, so that after all a much larger volume is produced [twice as much by .16 in. (4 mm.) per second velocity as with 1.56 in. (40 mm.)] without improving the clarification; for the amount of the dried material removed is as 17.9:15.9. These experiments, however, only lasted one day. In practice one can count on a greater con- solidation of water and sludge with a velocity of 0.16 in. (4 mm.) per second. The explanation of the result of this experiment is that with the greater velocity the finer particles of sediment, which are contained in a large quantity of water but which altogether com- prise but a small amount of dried solids, are carried into the receiving stream. If sedimentation tanks are used intermittently, i.e., if the sewage is retained in them for some time after filling, possibly from 2 to 6 hours, and is then drawn off, clarified, the amount of settled sludge is less than with a continuous flow. Sludge is always stirred up in refilling which does not settle again but passes out in the effluent. It does not pay to clean out the comparatively slight deposit from every filling, in which way this objection could be met. In London at Barking the proportion of sludge derived from intermittent treatment (with 2 hours' resting) to that from con- tinuous flow is as 1:3, but this is in part due to the short time allowed for resting. The difference in the volume and consistency of the sludge is marked between the operation of several tanks in parallel and in series. In the latter case a large amount of thick, viscous sludge is deposited in the first tank and a fine, greasy mass of less volume in the last. As cleaning out is therefore required less frequently in the latter, this system and also the sludge more nearly resem- ble those of septic treatment plants. In planning for the removal and utilization of sludge and the sums to be expended, the method of clarification should be con- sidered from the beginning. AMOUNT OF SLUDGE It is also desirable to possess more information concerning the amounts of sludge deposited by the different methods of clarifi- cation. 16 SEWAGE SLUDGE It is impossible to give final figures or formulae by which the quantity of sludge to be expected may be exactly estimated, for this must vary within very wide limits for the reasons already stated. Exact values can only be ascertained by experiments with the sewage in question, which should always be made in the case of large plants and especially where the sewage shows any peculiarity. However, we can usually judge of the quantity of sludge to be expected from the amount of suspended matter in the sewage. In this way Busing, starting with an amount of suspended matter of about 700 parts per million (g. per cbm.) and a ratio of mineral to organic matter of 2 : 3, knowing the volume of the sewage and considering the amount of matter retained by catch basins, etc., estimates an amount of suspended matter equal to 1/1000 the volume of the sewage. The limiting values he states as 1/750, from a rather concentrated sewage, to 1/3000, where water is liberally used. This corresponds to 0.076 to 0.307 cu. in. of dried material per gallon (0.33 to 1.33 1. per cbm.) or 1.63 to 6.58 cu. yds. sludge 90 per cent, water per million gallons (3.3 to 13.3 1. per cbm.) and 0.43 to 1.74 cu. yds. per 1000 persons (0.33 to 1.33 1. per cap.) daily with a water con- sumption of 26.4 gallons (100 1.) per day. With an assumed average of 1 to 1500 for normal sewage the last two values would be 33.2 cu. yds. of sludge per million gallons (6.71 1. per cbm.), or 0.88 cu. yds. per 1000 persons (0.67 1. per capita) per day. These values agree well as to the contained moisture with the figures of Imhoff (Proceedings of the Royal Experiment Station, Vol. VII) in which, from many analyses of sludge in England and Germany, the amount of dried material in sewage was established at 2.1 oz. (60 g.) per capita per day, when including storm water but not industrial wastes. This value gives, with an amount of water in the sludge of: 95 per cent. 2.1X20 = 42 oz. (0.06X20 = 1.2 1.) sludge per capita per day. 90 per cent. 2.1x10 = 21 oz. (0.06X10 = 0.6 1.) sludge per capita per day. 80 per cent. 2.1x5 = 10.5 oz. (0.06X5 = 0.3 1.) sludge per capita per day. We may approximate the same result by assuming an amount of suspened matter of 17.5 to 35 grains per gallon (300 to 600 mg. per 1.), as is the rule with city sewage in Germany. With a TREATMENT AND UTILIZATION OF SLUDGE 17 specific gravity of 1.1 we obtain 12.6 to 25.2 cu. in. per cubic yard (0.27 to 0.54 1. per cbm.) of dried material. As the larger floating substances are not included in the analyses this figure should be somewhat greater, so that 14 to 28 cu. in. per cubic yard (.3 to .6 1. per cbm.) of sludge containing 90 per cent, water may be expected. In estimating these values no account is taken of a partial elimination of the solid matter in the clarification plant. The efficiency of the method of clarification is therefore to be taken into account. These methods of estimating are valueless, possibly in the case of grit chambers, but particularly with screening or contact bed treatment. Here one must trust to experience and experiment. It is in any case of greater value to consider experience with the plants of towns where the conditions are similar than to depend upon theoretical calculations of the sludge to be expected. AMOUNT OF DETRITUS FROM GRIT CHAMBERS AND SCREENS American measures Metric n leasures Place Cu. yds. per million gallons sewage Cu. yds. per 1000 inhabi- tants per day Liters per 1000 cubic meters sewage Liters per 1000 in- habitants per day Method employed Leipzig 067 13 5 Coarse screen- Charlottenburg 014 11 ing. Grit chamber Hamburg Ohrdruf 0.826 0.056 0.079 167 43 60 and screening. Grit chamber and screening. Grit chamber Schoneberg Marburg Marburg Frankfort-on-Main Frankfort-on-Maia Cologne 0.643 0.643 0.643 356 0.021 0.027 0.022 0.038 0.038 130 130 130 72 16 21 17 29 29 and screening. Grit chamber and screening. Grit chamber. Screening. Grit chamber. Screening. Grit chamber. Cologne 905 183 Screening. Elberfeld 426 025 86 19 Grit chamber. Elberfeld Hanover. . 0.639 1.069 0.037 . 033 129 216 28 25 Screening. Grit chamber. Dresden 0.149 0.007 30 5 Grit chamber. Dresden Munich-Gladbach 0.500 0.371 0.022 0.076 101 75 17 58 Riensch disc. Screening. 18 SEWAGE SLUDGE The following tables give some results of the amounts of sludge obtained by various processes. The figures are obtained partly from reports and partly by direct information furnished by city authorities. The amounts may be estimated per million gallons of sewage or per capita per day. The first method is used in towns where much of the sewage comes from manufacturing concerns, while the latter affords a better comparison where these are absent, because the different volumes of water used are eliminated. It is further to be noted that in estimating the separate quanti- ties the volume of sludge is usually ascertained quite accurately by the mark of the surface level in the tank, by the contents of the vacuum receiver or the sludge-press, or that of the drying bed, while, on the contrary, the volume of the clarified sewage in a specified period, especially in towns with combined sewerage, is usually not closely enough ascertained. The results with these methods naturally vary greatly, especi- ally with bar screens and mesh screens, on account of the differ- ence in the size of the mesh and the spacing of the bars; but this is so with regard to grit chambers also, although in less degree, on account of the different velocities and other reasons already given. AMOUNT OF SLUDGE FROM SEDIMENTATION TANKS American measures Metric n tieasures Place Cu. yds. per million gallons sewage Cu. yds. per 1000 per- sons day Liters per cubic me- ter of sewage Liters per capita per day Method of clarification Frankfort 16.3 0.930 3.3 0.71 Tanks. Bremen 10.9 0.655 2.2 0.50 Tanks. Hanover 9.9 0.301 2.0 0.23 Tanks. Mannheim Munich-Gladbach Cassel Brieg 10.9 12.4 23.8 17 8 0.877 2.620 0.628 498 2.2 2.5 4.8 3 6 0.67 2.00 0.48 0.38 Tanks. Tanks. Tanks, i Wells. Stargard 37 1 589 7 5 0.45 Wells. Culmsee Langensalza Leipzig Leipzig 123.8 123.8 23.8 8 0.877 2.188 25. 25. 4.81 16 0.67 1.67 Tanks. Wells. Primary con- tact beds. Secondary con- Failswerth 2.8 0.092 0.56 0.07 tact beds. Secondary con- tact beds. 1 Without grit chambers and screens. TREATMENT AND UTILIZATION OF SLUDGE 19 With grit chambers we estimate 0.37 to 0.75 (average 0.50) cu. yds. per million gallons [75 to 150 (average 100) 1. per 1000 cbm.] of sewage and possibly 0.013 to 0.026 cu. yds. (10 to 20 1.) per 100 inhabitants daily. The same figures are to be used for bar screens. They are of course not correct for simple coarse bar screens which are only intended to keep coarse material from the pumps or plant. The amounts for these are much less, although with large screening plants they increase somewhat. In the larger German plants the amount of sludge is fairly uniform. It is about 10 to 25 cu. yds. per million gallons (2 to 5 1. per cbm.) or 0.39 to 1.31 cu. yds. per 1000 persons (0.3 to 1.0 1. per capita) per day. These differences result from the causes already mentioned, but above all from the water con- tained in the sludge. Therefore the places mentioned in the tables employing clarification by wells have comparatively large amounts of sludge. For example, the high figures for Langen- salza result from the continuous removal of fresh sludge. In Culmsee, on the other hand, the separate system exists and the sewage is fairly concentrated. Preliminary treatment by con- tact beds gives values similar to sedimentation, special weight being laid upon the greatest possible previous removal of sus- pended matter in order to protect the beds. Subsequent treat- ment, which is only used with sprinkling filters, on account of the particles of deposit frequently washed out, naturally shows but a small amount of sludge. AMOUNT OF SLUDGE FROM SEPTIC TANKS American measures Metric r neasures Place Cubic yards per million gallons sewage Cubic yards per 1000 persons daily Liters per cubic meter of sewage Liters per capita per day Manchester .... 12 0.62 2 43 0.47 Accrington Colne 7.9 7.4 0.18 1.6 1.5 0.135 Hampton Birmingham Stuttgart Merseburg Mullheim Unna Leipzig 1 . . 4.36 16.85 18.6 8.2 13.8 9.9 7.3 0.50 0.10 0.46 0.26 0.88 3.4 3.75 1.65 2.0 2.0 1.47 0.38 0.08 0.35. 0.20 Emscherbrunnen Halberstadt 47.5 0.13-0.33 1.26 9.6 0.1-0.25 0.96 Preliminary biological treatment in experimental plant. 20 SEWAGE SLUDGE With septic tanks the amount of sludge produced is less the more complete the septic action (Merseburg) . Where the sewage is chiefly domestic and without storm water, which always adds much mineral matter, the amount is about 0.13 to 0.26 cu. yds. for each 1000 persons (0.1 to 0.2 1. per capita) daily, or 7.4 to 12.4 cu. yds. per million gallons (1.5 to 2.5 1. per cbm.) of sewage. In the other case, as well as in the presence of much trade waste, the limit is increased to about 0.39 cu. yds. per 1000 persons (0.3 1. per capita) per day, or to 17.3 cu. yds. per million gallons (3.5 1. per cbm.). Therefore many of the English cities show much AMOUNT OF SLUDGE FROM CHEMICAL PRECIPITATION American measures Metric ir easures Place Cubic yards per million gallons sewage Cubic yards per 1000 persons daily Liters per cubic meter of sewage Liters per capita per day Precipitant Chorley Hendon Lichfield 79 69 29.7 3.64 2.98 16 14 6 2.78 2.27 Aluminoferric Aluminoferric Aluminoferric Sheffield Bury Guildford Glasgow London Leipzig Essen . . . 13.4 74 111.9 42 32.2 24.1 19.8 0.54 2.19 4.01 1.66 .80 2.7 15 22.6 8.5 6.5 4.87 4.00 0.41 1.67 3.06 1.27 0.61 Lime Aluminoferric Aluminoferric Lime and sulphate of alumina Lime and sulphate of iron Oxide of iron Lime larger amounts of sludge. In Halberstadt the high figure is attributable to the limited amount of digestion as the sludge is removed here every 8 weeks. Chemical treatment produces a varied amount of sludge de- pending upon the process employed and the amount of pre- cipitant used, as the latter produces a large volume of sludge containing much water. Thus, 1.71 grains of lime per gallon (100 g. per cbm.) of sewage, if the precipitation were complete, would give 2.2 Ibs. (1000 g.) of sludge with 90 per cent, moisture. But often .44 Ib. (200 g.) to even 1.1 Ibs. (500 g.) of precipitant are added separately. The increased clarification effected by sedimentation, possibly 75 to 80 per cent, of the suspended matter as compared with 60 to 70 per cent, by mechanical methods, TREATMENT AND UTILIZATION OF SLUDGE 21 results jn larger deposits of sludge. In general the amount is 25 to 50 cu. yds. per million gallons (5 to 10 1. per cbm.) of sewage. The low efficiency observed at Sheffield is explained by the fact that one-third of the sewage there is wash water. The lignite treatment, which is closely allied to chemical treat- ment, removes yet greater amounts of sludge, 100 to 125 cu. yds. per million gallons (20 to 25 1. per cbm.) of sewage, partly because a very watery sludge is obtained, partly because the lignite and sulphate of alumina increase the volume greatly by the absorp- tion of water. At Copenick on the other hand, where the sludge is obtained by drying out in the tanks to about 60 per cent, moisture, they get 12. 5 cu. yds. per million gallons (2.5 1. per cbm.), or 1.18 cu. yds. per 1000 inhabitants (0.9 1. per capita) daily. From the data given the amount of sludge to be expected may (in spite of some considerable differences) be estimated with sufficient accuracy for a given size of plant and the arrangements for its treatment and utilization. Chemical treatment gives the greatest amount of sludge and has, therefore, been abandoned in many cases, while the septic tank gives the least. The rule applies to all methods, that the more thorough the purification the greater the resulting amount of sludge. CHAPTER III THE REMOVAL OF SLUDGE FROM CLARIFICATION TANKS A well considered plan for removing the sludge from the tank and for its transport to places where further drying or treatment is carried on, is of great importance; for upon this rests the efficiency of various methods of treatment. Moreover, foul odors may in this way be minimized, if not entirely avoided, and large sums of money saved, especially in wages. The plants and their details, therefore, vary very greatly and in general must be adapted to the methods of cleaning and of operation as well as to the topographical conditions. The general principles to be observed in the treatment of sewage may be summarized as follows: 1. The more frequently sludge has to be removed and the larger its amount, the greater the attention that must be given to the matter and the greater the cost in any given case. 2. The condition of the sludge which is favorable for its later use must not be altered to its detriment in removal. 3. The removal of sludge must be accomplished with the least possible work. 4. This should be effected, so far as possible, without manual labor. 5. The removal should be as complete 'as possible. 6. With mechanical appliances it is important that all parts should be as simple as possible, especially movable parts, and that their location should be above water. Referring to 1, the periods of cleaning are largely dependent on the method employed. The removal of detritus from grit chambers usually takes place after the receptacles provided for it are filled, in order to avoid encroaching on the waterway and preventing insufficient sedimentation. A daily cleaning is only required where the amount removed is very large, as otherwise excessive dimensions for the grit chamber would be necessary, and this removal should then be by mechanical means. 22 TREATMENT AND UTILIZATION OF SLUDGE 23 With mesh screens and bar screens the detritus should, natur- ally, be constantly removed. Here, too, the removal in large plants is mechanical and automatic. The intervals between the removal of sludge from semimenta- tion tanks depend on the putrefaction of the material contained. This is controlled by the nature of the sewage and also by the temperature. Therefore the sludge may remain in the tanks 3 to 7 days in summer, 8 to 12 in winter. In chemical treatment these periods can be increased, especially when this method interferes with putrefaction. At Leipzig, e.g., the sludge is drawn off every 10 to 20 days. In septic tanks the sludge should be removed at much longer intervals. Its storage is here the important matter. With small installations removal need only take place from one to two times a year, in larger ones very one to three months. In general, an infrequent removal should be aimed at, as only in this way can the advantage of the septic tank be fully realized; for the amount is diminished by long storage, as has already been mentioned, and it also becomes less offensive. In any case an increase of suspended matter in the effluent caused by the accumulation of deposit and a resulting increase of velocity, indicate the time for cleaning. Another method, and one to be recommended in large plants with large volumes of sludge, is to draw off a part at shorter intervals during operation; while the main cleaning should be done in the fall and spring, especially where it is used as a fertilizer. When the removal is made, as at Leeds, through plug valves at the bottom, the result is the thickest and most thoroughly digested sludge and an objection- able interference with its free flow is prevented. Moreover, the tank is in continuous use and the sludge chamber can accommo- date smaller volumes (Emscher tanks). - The intervals between cleanings in contact beds are so varied, according to their construction and demands, that no figures can be given. The amounts of sludge from the different processes are given in the previous chapter. As to 2, the favorable condition of the sludge, especially the small amount of water contained, must not be altered in its removal. If sludge from septic tanks, for instance, must be stirred up so as to be removed by pumps, the proportion of water, and consequently the entire volume, is increased, although 24 SEWAGE SLUDGE the water is given off again more readily on account of its com- position than in plain sedimentation. In such cases sludge from the combined system leads to better results by drawing off the upper dilute layer by pumps, while the lower, settled layers are excavated, as in Unna. Sludge from plain sedimentation also contains more moisture where the stirring process or flushing pipes are used. With the Kremer apparatus, where the sludge of the bottom layer contains but 85 per cent, of water or less (as here the grease and cellulose particles which attract a large amount of moisture are removed), this preservation of the favorable consistency of the sludge in its removal is most important. Where the fine greasy material is removed separately by being passed through several tanks, the ability to keep it separate is desirable in order to work it over into grease, or else to bury it wet, while the coarser portion can be dried. 3. The work of disposing of sludge can often be greatly lightened by an intelligent use of the land. The places for drying sludge should therefore be located as low as possible in order to permit of its discharge from the tanks by gravity. This is especially desirable where the tanks are elevated above the sur- rounding land on account of an unfavorable soil for foundation and ground water (Rheydt) or where the entire plant is on sloping ground (Siegen). Much may also be gained by a favorable arrangement of the ground plan of the separate parts, such as tanks, sludge wells, pumps and beds and apparatus for drying sludge. As sludge containing much sand does not flow so readily and therefore demands a steeper slope in the bottom of the tank and in the pipes, it is advisable to place a good grit chamber for its interception. The suction of the pumps will then be more efficient and erosion lessened. Much labor can be saved by forethought in designing the tanks for the removal of sludge. The use of mechanical appara- tus, such as will be described later, will be of advantage in certain cases. 4. In spite of the large numbers of bacteria in sludge (over 11,000,000 per c.c. were found in one English examination of fresh sludge) the number of pathogenic germs is small. There- fore there is but little illness among the employees of these plants that can be traced to them. There is, however, some possibility TREATMENT AND UTILIZATION OF SLUDGE 25 that the germs of contagious diseases in a city may exist in the sewage and sludge in large numbers until they are sufficiently disinfected. For this reason, and because the exhalation from the sludge as it putrefies, as it almost always does in summer, are detrimental to the health of the workmen, their personal contact with the sludge should be avoided. The high wages required to get this dirty and unpopular work done can also thus be saved. 5. When portions of putrescent material remain in the tanks after the removal of sludge, the fresh sewage entering becomes contaminated and in a few hours septic. The bubbles of gas which form in septic tanks cause particles of sludge to rise and then pass out in the effluent or adhere to the contact beds, which may be inserted subsequently, hastening the process of sludging. In this connection all devices for drawing off the sludge from below the surface, and whose proper operation, therefore, cannot be observed, should receive careful supervision. Formerly but little weight was attached to this matter in England, and as the outflowing liquid became putrescent and carried off larger flakes of suspended matter, plain sedimentation tanks were abandoned in favor of chemical precipitation. If particles of sludge remain for any length of time in the tank they become compacted and their loosening and removal, per- haps by flushing nozzles or by stirring, always becomes more difficult. 6. It is unnecessary to point out that the principles applicable to all hydraulic work that of providing mechanical details of the greatest simplicity and strength and locating their moving parts so far as practicable above water are especially important in dealing with sewage and sludge. One favorable quality in sewage is to be noted: that the contained grease acts in many cases as a lubricant on the moving parts with which it comes in contact. REMOVAL OF DETRITUS FROM GRIT CHAMBERS Detritus is most frequently removed by suspending operation and cleaning it out with a shovel by hand after the sewage has been pumped off. For this purpose it is necessary to divide the grit chamber. A further division is sometimes made in the effort to maintain the most favorable velocity for depositing the mineral 26 SEWAGE SLUDGE matter by changing the flow of sewage by operating or cutting- out the different units. In smaller plants the deposited material is often collected in buckets set in a steeply sloping pit and these are lifted out by cranes. Larger plants are often provided with bucket dredges. These can be stationary provided the bottom has a steep slope (1:1) toward the dredge, but the movement in a vertical direction must be sufficiently great for it to be taken entirely out of the sewage after being used. This is necessary to avoid obstruction to the current of the sewage and to prevent the rusting of the bearings. In order to provide a steeper slope to the end walls with a greater length to the grit chamber it is advisable to pass the chain for the buckets over two pulleys, as in Figs. 1 and 2, as is done in Manchester. With a shallow pit the dredge must move horizontally. Sharp angles between bottom and side walls should be avoided, as these w r ill not be reached by the dredge and facilitate deposits of decomposing sludge. Cleaning may then take place during operation, as at Frankfort and Elberfeld. With very fine sand this may cause.trouble, as it will be stirred up FIG. 1. FIG. 2. FIGS. 1 and 2. Arrangement for cleaning grit chamber. and washed out by the dredging. For this reason the dredge was abandoned at Marburg. In place of the bucket-and-chain dredge a clam-shell dredge may be used, but, in order to prevent injury to the bottom, only when the plant is not in operation. On account of the depth of detritus in grit chambers, its removal by pumps or steam ejectors, as was attempted at Diissel- dorf, is not feasible, as the sand is mixed with water which then has to be again separated. At Merseburg, on the other hand, a Wegner patent portable suction pump was successfully employed, which will be spoken of later. TREATMENT AND UTILIZATION OF SLUDGE 27 The mechanical devices for the removal of detritus from mesh screens and bar screens, which are usually an intrinsic part of the plant, will not be particularly mentioned here. Further particulars may be found in Dunbar's "Principles of Sewage Treatment" 1 and Schmeitzner's "Clarification of Sewage. 7 ' 2 In smaller plants the cleaning is usually done by hand with rake or spade. Contact beds are taken apart for cleaning, and the material freed from deposit by rinsing or washing by hand or by machines, such as are used for gravel filters. REMOVAL OF SLUDGE FROM TANKS, WELLS AND TOWERS The question of removing sludge from tanks, wells and towers in sedimentation plants or from chemical precipitation tanks is of great importance. It is a question involving much larger volumes and also a more frequent removal made necessary by these methods of clarification. We may make a distinction at this point between (a) removal with interruption of operation, and (b) removal during operation. a. REMOVAL WITH INTERRUPTION OF OPERATION In this method the tanks are allowed to remain quiet for tanks are almost always used in this method for 1 or 2 hours after cutting off the supply. The clarified liquid above the sludge is then discharged into the outfall through an outlet con- trolled by gates or stop-planks. With a fixed overflow weir there is sometimes a special by-pass channel with a controlling valve. The turbid liquid which then remains in the tank above the sludge must usually be drawn off by pumps or a vacuum receiver, and conveyed to the influent conduit for a second clari- fication. Where there are several tanks it can be brought through a sufficiently deep connecting channel to a clean empty tank, in this way saving some cost. This tank is then filled with unsettled sewage and the process continued. The drawing off of the turbid liquid must be done in such a way that it is removed as completely as possible down to the under- lying layer of sludge without stirring this up. For this purpose a 1 "Clarification of Sewage," by Dr. Ing. Rudolph Schmeitzner. Translated by A. Elliott Kimberly. Eng. News Pub. Co., N. Y., 1910. 2 "Principles of Sewage Treatment," by Prof. Dr. Dunbar. Translated by H. T. Calvert. J. B. Lippincott Co., Phila., 1908. 28 SEWAGE SLUDGE movable weir, of which there are various types, may be used, or channels at different levels, such as are patented by the firm of Geiger in Karlsruhe, and have been furnished by them for Elber- feld. Here there is a drum whose casing is perforated by short spiral slits placed behind an iron plate with a vertical slit set in the wall of the tank. The liquid is gradually drawn off to lower levels by the rotation of the drum containing the slits which overlap those in the plate at different elevations. The same result is secured at Munich-Gladbach by a pipe which can be telescoped. At the upper end this has been en- larged like a funnel to secure a broad overflow and so avoid uneven disturbances. At Copenick the emptying of earth tanks having a capacity of about 3,440,000 gallons (1300 cbm.), is accomplished every 3 to 4 weeks in 2 days by 8 pipes of 5.85 in. (15 cm.) clear diameter placed at different elevations. These lie in a wall 9 ft. FIG. 3. Floating arm for drawing off supernatant liquid. 10 in. (3 m.) long, which also serves as an overflow weir, and are closed by iron flap valves set at the ends on the water side at an angle of 45 degrees. These are closed by the pressure of the sewage and can be opened by chains from above. This simple device has proved very efficient. All these arrangements, however, necessitate careful watching during operation. This is rendered unnecessary by the floating arm devices which were first used in England. Here there is a circular or square pipe attached to a fixed horizontal one, which can be swung in a vertical plane (Fig. 3). The upper end is always kept 8 to 10 in. (20 to 25 cm.) below the surface of the sewage by one or two floats. Consequently the sewage is only drawn off from the top layer. At the same time the opening being submerged prevents floating substances, TREATMENT AND UTILIZATION OF SLUDGE 29 such as scum and grease, from flowing off. The same purpose is sometimes served by a protecting box fastened between two floats (Fig. 4) or a floating scum board which cuts off a portion of the tank in which the floating arm is located and which moves in two grooves in the sides of the tank. A valve is inserted in the horizontal pipe to regulate the dis- charge. In order to draw the sewage from the tank more evenly, the pipe leading to the valve may be divided into two branches which drop to each side of the tank (Fig. 4) . //MfM^^ FIG. 4. Double floating arm. In employing a vacuum receiver for the removal of the turbid liquor the introduction of a well for this liquid is advisable, as this renders the effluent independent of the intermittent opera- tion of the apparatus. In wells where there is not room for such a floating arm, which must be longer owing to the greater depth, a hose may be used which can be lowered by a chain as the sewage is drawn down (Harburg), or the suction end of which is kept submerged by floats. In general there will be found no necessity for special devices in wells for the removal of the turbid liquor but the sludge pipes can be used for repairs and inspection purposes. After the roily sewage has been removed the sludge must be drawn off. For this purpose a sludge sump should be provided in the tank, from which the pump draws off the sludge directly, or a sludge well should be inserted. The best position for the sump in tanks with the ordinary inclination is directly after the inlet, as most of the sludge is deposited here. In the experiments at 30 SEWAGE SLUDGE Cologne with a velocity of 1.56 in. (40 mm.) per second in the 1.1 ft. (3.35 m.) long sump (which is placed at the inlet just in front of the regulating device for securing a uniform distribution of flow), about 45 per cent, of the sludge was deposited, while in the remaining length of the tank fully 130 ft. (40 m.) only 55 per cent, was deposited. With a velocity of 0.78 in. (20 mm.) the proportion was 51 per cent, to 49 per cent., and with a veloc- ity of 0.156 in. (4 mm.), 70.7 per cent, in the sludge sump and 29.3 at the bottom of the tank (Fig. 5). At the same time such a location of the sump prevents a silting-up of the cross-section and gives to the bottom of the tank an inclination toward the inlet favorable to effective sedimentation. On account of the opposing current of the sewage, however, the flow of the sludge is retarded 4ffrvm 20mm mm 29,3% S/% I 70,7% FIG. 5. Deposition of grit in grit chambers. While it was formerly thought to be advisable in constructing sedimentation tanks to place baffle walls and other impediments to the flow of the sewage in order to promote clarification, more recent methods aim rather at preventing detrimental currents and at removing the sludge as simply and economically as possible. For this reason the ground plan should be regular in shape and above all sharp angles and corners should be avoided from which it may be difficult to remove the sludge. Earthen tanks are not advisable for thorough sedimentation, as they require frequent cleaning and, even for experimental plants a lining of cement or planks (which have been found serviceable in Bremen) should be employed. Otherwise the clarification tank must be used for sludge drying as well, as the muddy bottom would be removed with the liquid, sludge. In drying sludge in tanks, too, it is well that the sub-soil should have some marked characteristic, such as a light color. Above all, it is impracticable to provide a tank with a natural bottom of sufficient slope to convey the sludge readily to the sump. TREATMENT AND UTILIZATION OF SLUDGE 31 This mere detail is of particular value in tanks, for it is a disadvantage in this type of clarification chamber that the sludge must be removed separately from a large surface, and in cleaning by hand must be pushed to the sump by wooden or rubber covered scrapers. With the frequent cleaning necessary in sedimentation tanks this results in a great deal of labor and expense. It is, moreover, harmful to the workmen, who must often wade up to the knees in sludge and inhale the noxious gases from the decomposing material. The attempt is therefore made to so construct the bottom of the tanks that the sludge, in pumping, will always flow by gravity to the pump well. The slope in general use, say 1:100 (Mannheim and Cassel) to 1:45 (Hanover) is not sufficient, for experience has shown that some aid by manual labor cannot be dispensed with in these tanks. For an easy, automatic flow with settled sludge containing at least 90 per cent, of water a slope of 1: 10 to 1:15 is necessary, depending on whether there is much sand and coarse material, or whether there is a fine, fluid sludge. Such a steep slope is not feasible with tanks 130 ft. (40 m.) long. In some tanks a channel for the sludge has been built in the bottom, which grad- ually increases in depth and, for example, in Mannheim with an inclination of the bottom of 1:100, is given a fall of 1: 50, in Munich-Gladbach one of 1:25. The attempt has been made, in addition to increasing the fall, to reduce the friction of the sludge in the deep channel relative to that spread out in a thin layer over the whole bottom. But even in this way it is not always possible to attain an automatic flow, as the inclination is still too small, and, moreover, on account of its fluidity, the sludge assumes a horizontal surface and does not flow from the sides into the channel and so into the sump, but spreads, rather, in a broad stream over the whole of the bottom. The channel, also, with its steep sides and curved invert, renders subsequent clean- ing by hand more difficult. To facilitate this, or, possibly, to install an arrangement for removing sludge which will be described further on, the tank should be built with a basket-shaped cross-section, or with straight lines and a steep diagonal slope, but without sharp edges or corners. In Frankfort-on-the-Main, to entirely avoid subsequent clean- 32 SEWAGE SLUDGE ing by hand, two sludge sumps were constructed in a tank 135.8 ft. (41.4 m.) long, and the bottom had a longitudinal inclination of 1:10 toward these (Fig. 6). The diagonal slope at the ends and in the middle was 1:3, and near the sumps 1:2 (Fig. 7). These have a diameter of 8.2 ft. (2.5 m.). Their bottoms are conical with an inclination of 1 :1. In addition, all surfaces exposed to the sewage are lined with glazed brick or, where this is not possible, as on small ri rounded angles, with smoothly | dressed sandstone. In this | way a perfectly automatic flow g, of sludge toward the sumps is g secured. Moreover, a pipe for water under pressure with ji many connections has been J laid, by the aid of which a J thorough cleaning may be 3 effected by jets, for the glazed g surfaces gradually become | coated with a sticky layer which increases the friction of o the flowing sludge. Further attempts to divide the bottoms of tanks into separate hoppers facilitate the flow of the sludge and aid particularly in its removal during the operation of the plant and will therefore be treated of later. In general every plant should be so constructed as to abso- lutely prevent any deposit of sludge in the receiving chambers, branching channels and entrance galleries by ensuring an ample velocity to the stream. We should endeavor to simplify the process by separating the sludge at as few places as possible TREATMENT AND UTILIZATION OF SLUDGE 33 because, from the lack of suitable provisions, the removal of sludge from these parts of the plant can seldom be accom- plished without interfering with the operation. The next step is to effect the concentration of the sludge in the direction of the pump pit by mechanical means, and thus lower the cost. FIG. 7. Development of cross-section of chamber with pump pit. In the plant at Bremen a kind of wooden sludge car of simple construction is used (Fig. 8). This is about 14.8 ft. (4.5 m.) wide and runs by means of flanged iron wheels on substantial plunks which project about 4 in. (10 cm.) above the wooden flooring with which the shallow tank at that place is provided. These shallow tanks, which are about 65.6 ft. (20 m.) wide, are therefore divided into 4 longitudinal strips corresponding to the 34 SEWAGE SLUDGE width of the car. The car has an adjustable squeegee on the forward side provided with a strip of rubber and is drawn by a rope from the effluent end to the sump at the inlet. The wind- lass is turned by the engine which operates the dredge, and as the rope runs over a guide-pulley it can be used for all four tanks. The return movement is accomplished by another wire rope which is drawn by a movable windlass operated by hand. This motion could have been effected by the engine already mentioned if the rope were led through guide pulleys around the tank, as Rubber Strip FIG. 8. Car for removing sludge. (Bremen.} customary with steam plows which are driven by one engine. To move the car across the end of the tank and for lifting across the wall separating two tanks, four wide rollers are used which can be inserted or removed by means of screws. Although where there is an accumulation of sludge, the car must make several trips, yet 78 to 92 cu. yds. (60 to 70 cbm.) of sludge can be removed from a large [commonly 32,300 sq. ft. (3000 sq. m.)] and nearly horizontal tank, by two men in one day, while for- merly it required nine men for perhaps three days to do this. Moving the car across of course makes it necessary for the men to get into the tank, but this is only at the effluent end where there is little sludge and occupies but little time. This has been avoided at Bolton by constructing in each of the shallow tanks, 328 ft. (100 m.) long, a sludge-pushing car (Fig. 9) TREATMENT AND UTILIZATION OF SLUDGE 35 which, on account of the narrow width of the tank, serves for the whole cross-section. It is said that all the sludge in the tank can be removed in 15 minutes. It is doubtful, however, if the sludge can be removed by this apparatus without also drawing off the upper layer of sewage; for the watery sludge, on account of the slight difference between its specific gravity and that of the sewage in a full tank, would probably rise in front of the car and flow over it, aided by the current induced by the motion. This cannot happen with an empty tank on account of the density FIG. 9. Ashton-apparatus for removing sludge from shallow tanks. (Bolton.) of the sludge with its contained water. With a rounded cross- section of the tank such an apparatus, modeled after a canal- cleaning car, could be used and could be driven by a light movable windlass, preferably run by electricity. The whole construction could be made much simpler and lighter by having the rope attached to the squeegee at several points. The question of a gain in efficiency depends upon a uniform cross-section for the entire length of the tank. b. REMOVAL OF SLUDGE DURING OPERATION 1. CONSTRUCTION The somewhat costly and troublesome process of removing sludge during a suspension of the flow led early to the devising 36 SEWAGE SLUDGE of ways and means for simplifying and cheapening the work by continuous removal. Wells were first considered for this purpose, because the comparatively small sludge tank, especially in chemical precipitation, which was then in general use, with its large volume of sludge, required frequent cleaning; while its form offered the fewest difficulties to continuous removal. Its principal advantage is in avoiding the costly removal of the turbid sewage, which in most places must be drawn off by pumps from tanks as well as from wells; and especially where the process necessitates frequent cleaning this is an important consideration. Moreover, the entire plant can be in use, while otherwise to avoid overloading it must be constructed of greater size in order to allow for those parts which lie idle during cleaning. It can be so designed, moreover, that only the dried sludge is exposed, provided closed pipes are used and the drying is done by a mechanical process described later on, so that the demands of hygiene are more completely met and foul odors are almost eliminated. But even if sludge is dried in the open air this method offers great advantages, especially if the places for drying are at some distance from the treatment plant. A disadvantage in most plants cleaned during operation lies in the fact that their sludge contains a greater amount of water, not less than 95 per cent. Where it can be utilized in this wet condition without further transportation or where ample areas for drying with favorable sub-soil and location are available, this matter is of less import- ance. In those plants, on the other hand, where the drying or hand- ling is done by machines whose size would have to be increased to correspond to the greater volume of sludge, one should consider whether the increased efficiency will pay for the greater outlay. As this manner of removing sludge always requires a material that will flow, it must often take place before it has fully settled. It is therefore especially adapted to thorough sedimentation, that is, where the clarified sewage is discharged to the stream without subsequent treatment and consequently must not be in a putrescent condition. The sludge shows an easily flowing con- sistency when it contains a small amount of grease, although it contains but little water. The Kremer apparatus is therefore particularly well adapted to the removal of sludge during opera- tion, because we have with it the separation of the fats and cellu- TREATMENT AND UTILIZATION OF SLUDGE 37 lose which are found in the partly clarified upper stratum of the liquid, while in the lower part we have the descending sediment. It goes without saying that one can never predict with cer- tainty regarding any of these details that all the sludge will be removed, and hence that there is no more putrescible matter present. Removal of sludge during operation is effected either -by the construction of the plant or by the introduction of some special mechanical device. Sometimes both of these means are em- ployed. A favorable concentration of the sludge at the bottom should be aimed at in the design. This end is most frequently attained Fia. 10. Dortmund tank. with wells. As already mentioned, these are almost universally arranged for the removal of the sludge without preliminary emptying. With their comparatively small dimensions it is usually easy to give the bottom such an inclination that the sludge will flow by itself toward the suction pipe of the sludge pump at the center. A slope of 2 : 1, as is found in the so-called Dortmund tank (Fig. 10) and which is also used in England, suffices for all cases. A slope of less than 45 degrees, as in the sludge well constructed in the clarification tank at Frankfort, will permit a slippery sludge to slide off if submerged. The angles between the vertical walls and the conical base should receive especial attention, as experience indicates that the sedi- 38 SEWAGE SLUDGE ment in the sludge settles here. This can be prevented to a certain extent by rounding these corners. Naturally, the degree of roughness of the bottom helps deter- mine the slope. In large plants it is well to make experiments with the sludge which comes from the sewage to be treated, unless the slopes have been determined by reliable experiments with different kinds of sludge on different surfaces from which it slips off by its own weight. It should furthermore be noted that in course of time a sticky coating is deposited on the smooth surfaces, reducing their efficiency very considerably especially in the case of smooth enameled or glazed surfaces and those of glass and that their cleaning necessitates a cessation of operation. The cone formed at the bottom of the wells corresponding to the natural slope of the earth will not suffice for a free removal of the sludge. It has been shown by experiments of Schoenf elder at Elberfeld that a steeper slope is required to secure an automatic sliding of the sludge if removed under water than if the supernatant liquid is first drawn off, and that special precautions should be taken in the process. Here it was observed that the sludge was deposited in horizontal layers not of uniform thickness, parallel to the bottom. When the sludge was drawn off at the deepest point a funnel was formed. After this the sludge failed to slide, although having a slope of 1:3; but this did occur immediately after draw- ing off the supernatant sewage. The explanation of this is that the difference in weight between the saturated sludge and the turbid sewage above is too slight to overcome the friction of the surface at the bottom and of the surface in contact with the turbid sewage; for the weight of the sludge is reduced by that of the displaced sewage, while in the case of empty tanks the weight of the sludge becomes effective. The funnel mentioned gradually closed in again under water so that in a half hour it was always smooth and horizontal. This was confirmed by experiments at Cologne. Here the sludge was to be pumped from under water out of sumps having a slope of 1 : 1. It soon appeared that after a few minutes only water came out, which found its way through the compact sludge near the suction strainer and carried with it only a few frag- ments of sludge which it was able to dislodge. This, which is also confirmed by practice and experiments elsewhere, proves TREATMENT AND UTILIZATION OF SLUDGE 39 that the removal of sludge under water and without stirring up the deposited material is only practicable before the sludge is firmly settled in place. The composition of the sludge is of importance in this connection as the greasy material forms a light but firm mass, while sludge from septic tanks which is kept in motion by frequent partial removal, as in the Emscher tank, and, by the gases rising from it, can easily be removed during operation. In these plants, which, as is known, are a combination of short sedimentation tanks, with septic chambers below, the difference in quality between the fresh and septic sludge is taken into account by giving the floor of the upper part a slope of 1 1/2:1, and in the most recent structures this is covered with glass plates laid on reinforced concrete supports to lessen the friction. Such precautions are necessary in order to induce the settled sludge to slide down in thin layers to the lower chamber as soon as possible. As the experiments of Grimm (which led him to introduce sedimentation plates in the tanks) have shown, this is promoted by the fact that colloidal matter has a marked tendency to form a gelatinous coating by friction, or even by contact, with a solid body. This is then set in motion on the steep surface by gravity, and in rolling down carries with it the particles of sludge which are in the way. In order to convey the septic sludge, which fills the lower tank in a great mass, to the sludge pipe a slope of 1 : 2 is sufficient, to which may be added a flushing pipe to be described later. The many other forms of wells which have been constructed in view of the particular end to be reached, and especially for chemical precipitation in all its different phases, more particularly with reference to the introduction and distribution of the sewage, are subject to the same principles regarding the removal of sludge as the Dortmund tank, given as an example. The same is true of the short, shallow tanks, having the base constructed as a pyramid, with sides sloping at 45 degrees or more in order to facilitate the removal of sludge. The advantage of this form is made evident by the simplicity with which the desired purpose is effected. The attempt has also been made in various ways to remove the sludge from the ordinary long shallow tank while in use. In Thorn the bottom of a tank fully 65.6 ft. (20 m.) long and 40 SEWAGE SLUDGE perhaps 26.2 ft. (8 m.) wide, having sides with a slope of less than 45 degrees was divided for this purpose into 4 parts (Fig. II) 1 by constructing saddle-shaped division walls, from the lowest point of which the sludge was led under water pressure to the sludge channel which was used in common for two tanks. A similar solution by the use of hopper-shaped bottoms has been employed by Schoenf elder at Elberfeld (Fig. 12), but their 0- Well for Clarifying with Lime Plan. Longitudinal Section. Transverse Section. Fia. 11. Sedimentation tanks at Thorn. dimensions have been made quite different for the following reasons: As the largest amount of sludge settles in the first quarter of the tank, as was observed in the Cologne experiments, the last hopper-shaped compartments, if the tank were composed of compartments of equal size, would require very much longer to fill with the fine sludge than the first ones in which the coarser constituents were settled out. In this way a separation of the sludge according to its composition was effected. This is particularly valuable because the fine sludge, on account of the 1 Fig. 11 is taken from Salomon's "Die Stadtische Abawasserbeseitigung in Deutschland," 1907. TREATMENT AND UTILIZATION OF SLUDGE 41 light weight of particles of fat, contains the most grease and can later be manipulated so as to separate this out, while the coarse sludge, on account of the small amount of grease, can be drained more quickly and easily. For this reason the sludge tank at Elberfeld is divided for the purpose of receiving these two kinds of sludge, without, however, any use being made of the device as yet. Another advantage is that the hoppers for the fine sludge can have less slope, on account of its greater fluidity, at least in the upper portion, besides being of smaller dimensions. Experiments with a model demonstrated that less slope was required for the concentration of the sludge under water, while a steeper one was required to avoid the formation of funnels while forcing it out. There- fore steeper hoppers were inserted to ensure a removal of the sludge. The easiest way to measure the height of the sludge in wells and tanks is by lowering a sheet iron plate attached in a horizontal position to a measuring chain. By the increased resistance to the vertical movement of such a plate in sludge in comparison with water one can determine with sufficient exactness the height of the sludge by reading from the chain. It is not sufficient to concentrate the sludge at one or more points under the sewage, but it must also be delivered, and herein lies a particular difficulty in the removal of sludge during oper- ation. The delivery of the sludge can be accomplished 1. by suction with pumps, vacuum receivers or similar apparatus in the same way as in its removal during suspension of operation; 2. by drawing it off by the aid of hydrostatic pressure, either toward a deeper channel or sludge well or, under pressure, through a rising main, so that it is dis- 42 SEWAGE SLUDGE charged but a little below the level of the surface of the sewage in the well or tank. The insertion of a sludge well in making use of vacuum appa- ratus is of advantage, as in this way a uniform flow of the sludge is procured and fluctuations of the flow resulting in the entrain- ment of larger amounts of water, as may readily occur by the intermittent operation of such an arrangement, may be avoided. Moreover, this permits observation of the amount of water con- tained in the sludge delivered from plants to which it is adapted; which is otherwise only possible at the end of the rising main, and as this is often at some distance from the clarification plant, it is impracticable. In forcing sludge through a rising main there should be a difference in elevation of 2.6 to 3.3 ft. (0.8 to 1.0 m.) between the surface of the sewage and the discharge end of the pipe with ordinary settled sludge. With the Emscher tank this should be increased to 5.0 ft. (1.5 m.). Here two flushing pipes are pro- vided for water under pressure of which one, forming a ring, is perhaps at the elevation of the connection between the cylinder and the conical base, and, with its orifices directed downward, is intended to assist the sludge in sliding down the gentle slope of the base. The second terminates opposite the entrance to the sludge pipe in a loop with three orifices directed toward the center. This serves as a supplementary aid and to start the flow in case large masses of grit should collect there. As a failure of such plants is usually through refusal of the sludge which has accumulated in the pipes during a cessation of operation to flow after opening the valve, it is advisable to provide the sludge pipe with a branch pipe from the water main, as has been done with the Emscher tanks, so that the pipe may be filled with water after each emptying of sludge and the remaining sludge forced back to the tank. By means of these pipes positive action can be secured under difficult conditions, as the author can testify. The use of the two last-mentioned pipes is always well w r here there is difficulty in forcing out the sludge, especially in large plants where there is almost always water under pressure avail- able for flushing purposes. The sludge pipe should always be as straight as possible, avoiding sharp curves, which cause a loss of pressure. In conveying sludge under pressure where the operation is not continuous, care should be taken, in starting its movements, to TREATMENT AND UTILIZATION OF SLUDGE 43 avoid the formation of the funnels already mentioned. For although the water exerts a uniform pressure on the nearly horizontal surface, the vertical column of sewage over the pipe entrance will be set in motion by the sudden opening of the valves and will then settle and so increase the height of the column above. This, with the friction of the masses of sludge on the bottom and sides, helps in the formation of a funnel. This can be effectively prevented by a device called a sludge cylinder (German Patent) of the Company for Sewage Purifica- tion (Berlin-Schoeneberg), which can be attached to their FIG. 13. Kremer apparatus. Kremer apparatus (Charlottenburg) (Fig. 13). The bottom of the tank converges to a hopper having an inclination of less than 60 degrees with the horizontal, and is continued as a cylinder 2 it. 7 1/2 in. (0.8 m.) in diameter, in which the sludge is collected. The sludge pipe ends at the bottom of this cylinder, and through this the sludge is removed by hydrostatic pressure. The forma- tion of funnels with the resulting discharge of sewage is not possible in the narrow cylinder, so the sludge, which contains comparatively little water in the Kremer apparatus (80 to 85 per cent.) is removed from the tank without change in its favor- able composition. 44 SEWAGE SLUDGE 2. MECHANICAL CONTRIVANCES FOR REMOVING SLUDGE DURING OPERATION These mechanical devices may be classified as follows: 1. Those which, by stirring, mix the required amount of water with sludge that is not adapted to continuous removal, or at least assist in initiating its movement. To -the Air Pump -19 -Hie Pipe fvr Draining pur* rvn *m= = = Sewage Influerrf-- FIG. 14. Stirring device and skimmer in sedimentation tower in the lignite process. 2. Those which collect the sludge at certain points, from which it may be readily conveyed. 3. Those which, without materially affecting its settling, draw the sludge off from the place where it has been deposited. The stirring devices of the first category act in opposition to the principle laid down at the beginning of the section, that the TREATMENT AND UTILIZATION OF SLUDGE 45 consistency .of sludge should not be detrimentally altered in removal, and are therefore to be avoided as much as possible. They are sometimes installed later if the sludge does not flow of itself on account of too flat a slope in the bottom. If removal takes place during suspension of operation, the height of the stirring device above the bottom should be adjustable from above, so as to be always in contact with the top layer. (Wells at Mairich, Neustadt O.-S.). The chief occasion for their use is in the towers used in lignite treatment, as stirrers can only be used in wells or towers. They are commonly provided with a device for maintaining a light contact with the sludge surface and are kept continuously in slow motion (Fig. 14). The flush- (Skimmer '" .Sludge Gate FIG. 15. Skimming apparatus and sludge tank in the Kremer apparatus. ing pipes with water under pressure, already mentioned, as well as arrangements for securing the flow of sludge by compressed air, should be included here. Stirring the sludge is said to pro- mote its digestion in Emscher tanks, but disturbs uniform set- tling in sedimentation tanks. Arrangements for concentrating sludge are based upon the same idea as the apparatus described for use during suspended operation, but the construction may be lighter as the volumes of sludge to be disposed of on account of more frequent removal are smaller and do not offer so much resistance. In an experi- mental Kremer apparatus at Charlottenburg a simple surface scraping apparatus was found serviceable in a square tank with a flat bottom. The apparatus (Fig. 15) consists of a scraper in the shape of a board which can be turned on its upper edge 46 SEWAGE SLUDGE .-Supply Channel Entrance g" Dicimt Discharge Effluen+ > Channel Well for Sludge Valve FIG. 16. Spiral shaped sludge collector. (Fidler Patent.) Sludge Discharge '^--Rotary Sludge "^^ Discharge Pipe FIG. 17. Sedimentation tank (Candy system) with rotary sludge discharge pipe. TREATMENT AND UTILIZATION OF SLUDGE 47 during its reverse motion. This scraper is operated by two vortical rods which are attached to a small four-wheeled car running on rails placed over the upper edges of the tank and moved by hand. The scraper in the stirring device of the lignite process towers operates in the same way, and for wells having a very steep base a scraper composed of a vertical scraping board which forces down the particles of sludge^ adhering to the walls may be found useful. The motion, which can be transmitted by gearing, should be very slow in this, as in the following apparatus, to avoid the formation of detrimental currents. The patent sludge collector of Fidler works by collecting the sludge by a rotary motion and can be installed in wells having a flat bottom. It is also used at Bolton in a long rectangular tank, where several such appliances are placed side by side. On account of the dead corners some supplementary hand labor is required, however. As shown in Fig. 16, the sludge gatherer consists of a spiral-shaped iron band which is set in motion by a hand-operated gear and which sweeps the sludge to the center, from which it is drawn off by suction or forced out, as illustrated in the cut. Twelve large wells on this system have recently been installed at Bury. The arrangement in the third category consists of a perforated pipe laid close to the bottom and connected with the sludge pipe and into which the sludge is forced by the pressure of the water. A rubber squeegee can be attached to this pipe which scrapes the sludge from the bottom. Fig. 17 shows such a pipe in a well of the Candy system. This is also connected with a wall scraper. Motion is derived from a gear-wheel operated by hand. The same principle applied to a shallow tank is shown in Fig. 18, representing a plant in Hey wood. The perforated pipe is guided here by two rack rails into which the pinions conveying the motion engage. The sludge is here raised up by a siphon over the side wall and into a channel which is common to two tanks. A pressure of 3 ft. (0.90 m.) is sufficient. The siphon is started by cutting out the upper part by the valves a and b which is then charged with a pump operated from the same platform as the moving machinery. The horizontal suction pipe is provided with a rubber squeegee. A disadvantage in this form is that important moving parts of the machine are submerged. These contrivances for removing sludge require for reliable 48 SEWAGE SLUDGE operation a liquid, easily flowing sludge and must therefore be cleaned out every day, or at least every two days. The sludge obtained contains about 97 per cent, of moisture, as the turbid sewage finds its way to the entrance more readily than the sludge is drawn off from the bottom. With a pipe which rotates about a central axis it follows that the motion is slower near the center of the tank, while the friction is reduced on account of the short length of the pipe; therefore more sewage is taken in here. As this sludge, with 97 per cent, of moisture, has twice the volume of that with 94 to 95 per cent, in the Dortmund tank when in operation, with the same amount of dried matter, the use of this method of collecting sludge is seldom to be recommended. Besides, with a larger proportion of mineral matter, as often FIG. 18. Movable sludge discharge pipe for sedimentation tanks. occurs after a thunder storm, the operation is more difficult and uncertain. In the Fidler system this is not the case. As sludge containing less water is secured here, while its delivery remains the same, this should have the decided preference. While the aim of all these structural or mechanical arrange- ments for removing sludge during operation is to collect the material in clarification tanks, or at least to draw it from these directly, there are some which enclose it in a special chamber or compartment without removal of the supernatant sewage, the intention being to prevent subsequent admission of the turbid sewage and its mixture with the sludge and to secure the latter as free as possible from moisture. It is well to consider here the introduction of a partition wall with a valve (sluice gate) leading into the sludge chamber which has been found valuable in the Kremer apparatus at Charlotten- burg (Fig. 15) and has also been used in similar plants by the Sewage Purification Company. This permits a discharge of the accumulated sludge with no fear that the turbid sewage will pass TREATMENT AND UTILIZATION OF SLUDGE 49 out with it. The sludge can be drawn off from here, in which case a pipe for the admission of air should be inserted from the sludge tank to above the surface of the sewage, or it may be forced out by the introduction of compressed air. Grimm (Gesundheits Ingenieur, 1909) attempts to apply the foregoing principle to shallow ;tanks in a somewhat different way. The bottom is divided into hoppers 10.76 sq. ft. (1 sq. m.) in area with side slopes of 45 degrees, from whose lower points vertical pipes lead, each row of which is connected by a trans- verse pipe (Fig. 19). The sludge slides into these pipes, which have a diameter of 3.9 to 5.9 in. (10 to 15 cm.) and may increase in size at the bottom, and its separation is facilitated by hoods or plates, according to Travis' theory, through which the water is Fio. 19. forced out. The height of the accumulated sludge can be observed for each transverse row of hoppers in a glass stand pipe connected with the sludge pipe at the traverseable sludge pas- sage-way. 1 When the depth is sufficient, the tops of these sludge pipes are closed by plugs carrying an air pipe reaching above the surface of the sewage and rendered accessible by a movable foot bridge. When the valve of the sludge pipe at the passage-way is opened, the sludge is discharged by gravity or suction, while air enters by means of the aforesaid air pipes through the plug valves. When the sludge is drawn out and the gate valve closed the pipes will fill again with turbid sewage by opening the plug valves and are then ready to receive sludge once more. By this arrangement, if the plug valves are tight enough, the subsequent entrance of turbid sewage is prevented; that is, a dry sludge is secured by allowing it to accumulate in a thick layer. By providing a steep slope in the cross pipes the 1 In the division wall between the tanks. Trans. 4 50 SEWAGE SLUDGE flow will be facilitated. In order to realize all advantages, however, this plant requires conscientious superintendence. A company for the purification of water and sewage at Neu- stadt a. d. H. has a patented device called a sewage preparer which prevents the sludge, that has accumulated in the sludge channel of a short tank having steep slopes on each side, from passing through the tank with the current, by a series of hori- zontal shutters operated from above. This is said to reduce the friction in continuous treatment and facilitate sliding. If the shutters are laid flat they shut off the sludge channel on the side of the tank, leaving an entrance only at the Upper end. By opening the gate valve sludge will be forced out of the channel by the pressure of the sewage above, as though from a tube. It is doubtful, however, whether the shutters in the lower part of the sludge-filled tank can be closed tightly enough to prevent the turbid sewage from mixing with the sludge in large quan- tities, especially in the neighborhood of the outlet, as the moving parts are mainly under water and cannot be constantly watched. c. CONTRIVANCES AND CONDUITS FOR CONVEYING SLUDGE Various contrivances have been employed to remove the grit from clarification tanks in case the sludge cannot be forced out by the pressure of the sewage above. These are: 1. Dredges. 2. Pumps. 3. Vacuum apparatus. 4. Various other contrivances. 1. As already remarked, dredges are chiefly used to clean out grit chambers. The transport of the material in large plants is often accomplished, by belt conveyors. Dredges should not be used to remove sludge from clarification tanks, especially during operation, as a thorough cleaning with them is not possible. It is also better to use other contrivances in sludge wells, on account of the dirtiness of the operation. 2. In using piston pumps the great difficulty encountered is to keep them water-tight, as they soon become worn out by the sand brought in. The valves, also, often interrupt operation and should therefore be placed where they are readily accessible. Hence it is an advantage to have a good grit chamber for the protection of the pumps. It is also to be noticed that in very TREATMENT AND UTILIZATION OF SLUDGE 51 sandy sludge the suction lift is reduced, so that pumps and vacuum apparatus must be placed lower. Coarse bar screens are also necessary with all kinds of pumps, to prevent pieces of wood or other coarse material from injuring the pumps. If these coarse screens are placed in the tank in front of the sludge channel or sump, as at Mannheim or Munich-Gladbach, the amount of the screenings will be less, because much of it, especi- ally lumps of fecal matter, disintegrate in the tank; but their removal from the bottom is less cleanly and more troublesome. It is advisable to install a sludge well where the sludge is not removed during continuous treatment, as the pumping plant may then be made smaller without increasing the time of re- moval. With a very viscous sludge it is of advantage to have a stirring device operated in connection with the pump. Diaphragm pumps, such as those furnished by Bopp and Reuther of Mannheim for the clarification plant at Hanover, are superior to ordinary piston pumps and are also much used else- where. Here the piston works in clean water, which conveys the pressure through diaphragms to the sludge which is to be delivered. Centrifugal pumps are also well adapted to the transport of sludge, but it is important that the impeller should be accessible. With sandy sludge there is a great amount of wear on the packing rings. They are particularly serviceable in pumping roily water because of their simple design, especially when operated by elec- tricity. By means of connecting pipes they can also be used for reserve power in pumping sludge. For small plants and as a reserve in those where sludge is propelled by hydrostatic pressure, the well-known diaphragm pumps are very useful. 3. With a vacuum apparatus it is well to connect two receivers, so that the air drawn from one will serve to force the sludge from the other, which was previously filled. The air pump must therefore be arranged to act as a vacuum and force pump. The operation of the valves is then automatic. To prevent the sludge from running into the air pump a U-shaped pipe should be inserted between it and the receiver, the top of which should be at least 33 ft. (10 m.) above the highest level of the sludge. Vacuum receivers are especially necessary where, from absence of grit chambers and screens, much coarse material is mixed with the sludge. They may also be used to propel the sludge for 52 SEWAGE SLUDGE long distances. In Oppeln the sludge is forced 3600 ft. (1100 m.) in a pipe 12 in. (300 mm.) in diameter. They, however, occupy more space than pumps. The patent Wegner vacuum wagon works on the same principle as the vacuum receiver. Here, in a portable receiver which can be used to transport the sludge, the air is rarified by ex- ploding benzine, causing the sludge to be sucked in. This apparatus is especially recommended for use with very small plants where, because of the proximity to improved property or public works, it is desirable to have an odorless removal of the sludge without the necessity of constructing a special plant for pumping it. As the receiver can be brought to any tank or well, the cost of sludge pipes is saved. The removal is also odor- less. This mode of operation has been found very satisfactory at Merseburg. In some cases the pneumatic apparatus used for cesspool cleaning can be used in the same way. 4. The steam ejector, among other contrivances, should be mentioned next. This has not been found useful in cleaning grit chambers on account of the consistency of the detritus. This difficulty might not hold in the case of the liquid sludge from tanks, but the disadvantage of the large consumption of steam outweighs the advantage due to its simple construction and the small amount of room taken up. In sewerage systems in which the sewage is lifted by compressed air their use may be considered. In the recently installed plant at Siegen an effort was made to convey the detritus of the grit chamber which lies at a high elevation, by means of a horizontal spiral screw delivering into a tip car at the outlet end, without interrupting operation of the plant, but as yet without success. Sludge pipes should always be accessible on account of the liability to stoppage, and should, therefore, not be enclosed in masonry for any great length. It should, moreover, be possible to produce a strong scouring current by water pressure or by the aid of sludge-propelling devices. Sometimes an open traversable channel between the tanks, in which the pipes are laid (Elberfeld) or into which the short sludge pipes open from the side (Mairich plant at Guben and Ohrdruf), serves as a sludge channel. This has the advantage, where sludge is removed during operation, that one can see the amount of water removed as soon as it comes out and act accordingly. The advantage of the possibility TREATMENT AND UTILIZATION OF SLUDGE 53 of using a pipe which opens into the sludge-well as a siphon to produce suction is, however, lost. The open channels to convey the sludge to the drying beds, which are intended to be used in the day time, should have the maximum hydraulic radius in order to reduce the friction. The inclination which should be given pipes and channels to secure a flow of sludge without assistance depends upon its nature and should not be too light. Very liquid sludge, with about 95 per cent, of water and but little sand, may under some circumstances be given a slope of 1:100, but 1:80 is better. For sludge obtained with interrupted operation a fall of 1:40 to 1:50 is necessary. The plants of the Emscher Association have grades of 1 : 20 to 1 : 40, while the pipe conduits at Elber- f eld have 1:30. Enclosed pipes are always preferable to open channels for hygienic reasons, especially for long distances. Moreover, the sludge is more readily moved and deposits of sludge can be more easily flushed out. The valves in the sludge pipes should be strong and simple. Those which have a bearing on one side only should have the operating screw on the outer side engaging in a rack on one side only. Valves in pipes should be designed without a bottom groove, and should bear on the narrow edges of the disc in order, to prevent an accumulation of coarse material which would prevent the valve from closing. CHAPTER IV REDUCTION OF THE WATER IN SLUDGE The large amount of water in sludge is a drawback to its use in any way and reduces its value on account of the work involved in its reduction. If it is used while wet the valueless water it con- tains limits the area to which it can be applied, on account of the increased cost of transportation. Moreover, this liquid condi- tion adds to the difficulty of transportation, as this can only be accomplished in water-tight vessels, and temporary storage in the field is impracticable without much preparation and apparatus. With perhaps 75 per cent, of moisture it can be loaded with a shovel and does not require a perfectly water-tight vessel. With 60 per cent, of moisture it is quite firm and resembles damp garden mould. It should therefore be reduced to this condition. Fig. 20 shows at a glance the relation between the amount of water removed and the consequent reduction of volume. The curves represent sludge of different degrees of original moisture, volumes in per cent, of that from which the water has not been extracted being represented by ordinates, while the abscissas represent the degree of de-watering in percentage of moisture contained in the whole. The horizontal line limits the volume of the dried residue, which remains constant. The distance of the curve from this line gives the amount of water contained in the sludge. It can be seen here how much water should be removed to reduce the amount in a wet sludge by 10 per cent, and how the quantity of water necessary to reduce the moisture to a given percentage rapidly diminishes. For example, from 100 Ibs. of sludge containing 90 per cent, of water (Fig. 20) 50 Ibs. of water must be removed to reduce it to 80 per cent., while reducing the same original volume from 60 to 50 per cent, requires the removal of but 5 Ibs., and from 30 to 20 per cent, only 1.8 Ibs. A comparison of the different curves shows by the steep slope on the right hand side that is, at the commencement of de- 54 TREATMENT AND UTILIZATION OF SLUDGE 55 watering how important it is for subsequent drying and treat- ment in general to have the sludge as dry as possible from the beginning; for the increase in the water content of the sludge corresponding to an increase of, say, 5 per cent, of moisture, has a varied effect, according, as we obtain a sludge containing 80 per cent, instead of 75 per cent, or sludge of 95 per cent, instead of 90 per cent, moisture. This is also of importance in considering the arrangements for treating the sludge described in the last section. 10 10 30 40 50 60 70 80 90 Amount of Water in the Mass afrer -the Watering, {95% 90% 80% 60% FIG. 20. Reduction of volume in sludge with extraction of water. On the other hand, it is recognized that drying beyond 50 per cent., at least with the very wet sludge from tanks, has but a slight effect on the reduction of volume, and for this reason alone further de-watering is not warranted. For example, sludge originally containing 95 per cent, of water has, when dried to 60 per cent., but 1/8 of the original volume, and so the cost of transportation is correspondingly lessened, and the extent of its use as a fertilizer is increased, as the amount of dried material, which alone is of value, remains unaltered. The following requirements should be observed in the process of de- watering: 1. The drying should not involve too great an expense, so that the expected increase in value of the product is not lessened. This may be accomplished by removing the water, by incinera- 56 SEWAGE SLUDGE tion, for instance, thus facilitating its transportation and a more rational utilization. 2. It should be effected rapidly, especially when done at the plant or in the neighborhood of habitations, in order to avoid accumulations of filth. 3. The operation should produce no nuisance in the neighbor- hood from foul odors or otherwise. 4. Handling of the sludge by workmen should be avoided, for reasons already stated. The methods of removing the water are as follows: a. Drying in the air. b. Drying by filter presser. c. Drying by centrifugal machines. d. Other methods of reducing the moisture. a. DRYING IN THE AIR Drying in the air is the process most commonly employed, especially with small plants. For this purpose the sludge is conducted into shallow basins. These are surrounded by earthen embankments or, less frequently, by slope paving, wooden sides or solid walls. The drying is effected in part by evaporation of the water and partly by its drainage into the underlying soil. If this is porous, subdrainage at a depth of about 2.3 ft. (0.7 m.) with a small distance between the separate lines of pipe is sufficient. Sometimes even this is unnecessary. In some cases, however, an artificial construction of the bottom, similar to a filter, is necessary, as with the natural subsoil the accumulation of sludge increases, so that it becomes necessary to remove and renew it. The depth of such a filter is usually 15 to 24 in. (40 to 60 cm.). The drainage channels, about 4 to 6 in. (10 to 15 cm.) wide, are laid with open joints at a distance of from 4 to 10 ft. (1.2 to 3.0 m.) apart and are covered to a depth of 12 to 16 in. (30 to 40 cm.) with cinders from boilers, pebbles or coarse gravel. A thick covering of fine cinders or screened gravel [2 to 4 in. (5 to 10 mm.) in size] follows this, 4 to 6 in. (10 to 15 cm.) in depth. This layer is to prevent the sludge from penetrating further into the filter. As the topmost layer becomes choked with sludge and portions of it are carried off with the dried sludge, it has to be renewed from time to time. To prevent this the bed may be covered with heavy stone paving, or, as at Leipzig, with TREATMENT AND UTILIZATION OF SLUDGE 57 a layer of bricks. The joints are then merely filled with sand. As all the water drains through these comparatively narrow spaces they soon become clogged with sludge, and the entire pavement must be taken up and renewed. The liquid drained off, which is usually somewhat turbid, owing to particles of sludge, and also putrescible, may be led to the intake of the clarification plant and treated again. As the volume is comparatively small, it does not alter to any great extent the sewage to be treated. In many cases this is impos- sible without long conduits or even devices for lifting it, espe- cially where the sludge is removed by hydrostatic pressure and brought by gravity in open conduits to the drying bed. In this case a small supplementary tank for subsequent sedimentation or a filter (Elberfeld) for the sludge liquor is advisable. If the sewage is subjected to subsequent purification by contact beds or sprinkling filters the sludge liquor can receive further treat- ment there. The liquor from drying beds after septic treatment requires no further treatment and may be led directly to the outfall, being odorless, clear and nonputrescible, as shown by the plants of the Emscher Association. By this method most of the water sepa- rates out in the first 12 hours and the sludge floats on account of the expansion of the contained gases, while a layer of clear water is formed underneath. The water should be drained through the filter as quickly as possible, for after the gas has been given off, at the end of 15 or 20 hours, the sludge sinks, due to its specific gravity, and the water rises over it. The same phenom- enon is observed in the deep sludge pit at Leipzig, except that here the water is not drained off from below, but is allowed to evaporate after it has risen above the sludge. With very greasy sludge it is sometimes impossible to draw off the water at the bottom, as at Frankfort-on-the-Main and Mannheim, as the particles of settled sludge form an impenetrable layer. The small amount of water on top can then only be drained off in as many places as possible through openings in the surrounding walls, which can be closed. If fresh sludge is discharged on top of beds of partly dried sludge, as can scarcely be avoided where the sludge is seldom cleaned out, it will dry more slowly on account of the heavier liquid beneath. The boundaries of the basins can be wholly or partially made of a sort of woven brush-work, thus obtaining a 58 SEWAGE SLUDGE lateral removal of the water through these, boundaries (Elber- feld, Halberstadt) . Nevertheless, the efficacy of this mode of draining the sludge is greatly diminished by the fact that the rapid delivery of the water through the brush and the influence of the air in drying the accumulation of deposited matter at the sides soon make a nearly impervious layer, because the moisture does not come rapidly enough from the interior. At Halber- stadt, therefore, it is not considered advisable to retain this device. At Bremen the basins were subdivided for this purpose by perforated planks, between which narrow passages were left for drawing off the liquid that leaked through and for removing the FIG. 21. Sludge beds of the Recklinghausen Clarification Plant. dried sludge; but this device was removed because the sludge found its way through the holes, making its handling mo're uncleanly, without resulting in a more rapid drying. If this is to be accomplished the sludge should be brought into the basin in thin layers, 6 to 10 in. (15 to 25 cm.) in thickness, and the basin should be filled as rapidly as possible, in order that the free removal of the water at the bottom may not be made more difficult by sludge which has had its moisture drained off. Small, shallow tanks are therefore to be preferred. These can be economically provided in small installations by construct- ing a border of planks placed on edge. In this way the excess area required by earthen embankments is utilized. (See Fig. 21.) TREATMENT AND UTILIZATION OF SLUDGE 59 In the cut, which shows the plant of the Emscher Association at Recklinghausen, the sludge running into an empty compartment may be plainly seen on the right. The sludge is forced out by hydrostatic pressure from 6 Emscher tanks lying beyond. In order to maintain a uniform depth of 'the layers the bottom should be made horizontal, as the sludge, due to its fluid nature, assumes a horizontal position. A disadvantage of plants with small, shallow basins lies in the greater cost of removing the dried sludge, as this comes in thin layers and necessitates frequent re-location of the rails for transportation, unless these are laid on an elevated trestle, as at Recklinghausen. This is obviated by the use of wheelbarrows. In selecting a location for the drying beds care should be taken that, with a porous soil, there are no wells in the vicinity that can be contaminated by infiltration. Especial care should also be taken with reference to odors and the plague of flies. These nuisances have again and again led to attempts to replace the cheap method of drying in the air by others, even though more expensive. As partial decomposition accompanies the operation of drying the foul odors caused by gases arising from the sludge, especially in the summer, give much discomfort to persons working or living near the plant. It may even result in lowering the value of land in the vicinity and cause great expense for indemnifica- tion. Likewise the plague of flies is very troublesome in the neighborhood, as the fermenting sludge offers an admirable breeding place for all kinds of flies and gnats. An attempt has been made to prevent this nuisance by adding some substance to the sludge. Such substances are either in- tended to stop putrefaction or else to form a cover to the sludge. In Cassel, for example, as well as in other places, lime has been successfully added to the sludge in the basins and at the outlet in the proportion of 6.8 Ibs. per cubic yard (4 kg. per cbm.). The nuisance of flies is done away with in this way, but, at the same time, the fertilizing quality of the sludge is reduced. In Frank- fort-on-the-Main, however, the addition of quick lime and chloride of lime has not had the desired result. Peat is found particularly desirable as a covering, and also to prevent odors, besides aiding the process of drying by absorption of the water. It is used in many places, especially where it is cheap. In order to prevent putrefaction it should be intimately 60 SEWAGE SLUDGE mixed with the sludge in large quantities. This is not prac- ticable, however, for economic and hygienic reasons. The use of manufactured deodorants, of which there are several, is more desirable. Among these "facilol," made by the tar product factory "Biebrich" at Biebrich has been found effective. It is a thin, brownish, light oil with a specific gravity of 0.79. It forms a coherent film of oil when placed upon water, which closes imme- diately if broken by gas bubbles or sudden currents, preventing the escape of odors. About 28 per cent, of facilol is composed of soluble substances of the phenol group, the effect of which is to prevent putrefaction in sludge and sludge liquor. The eggs and larvae of insects are also killed by it, while, at the same time, the covering prevents the insects themselves from obtaining their food. The facilol is sprayed upon the surface of the sludge immedi- ately after its entrance into the basins by a spraying device. The film of facilol is maintained intact by subsequent spraying at long intervals. According to information furnished at Frank- fort 0.11 to 0.18 gallons of facilol per square yard (0.5 to 0.8 1 per sq. m.) of surface will suffice. The price is about $2.15 per 100 Ibs. (20 m. per 100 kg.). This mode of deodorizing, there- fore, though efficient, is rather expensive. As the intensity of the odors increases with the area exposed it might be well to put the sludge to be dried in as deep pits as possible whose bottoms have been drained, and this has, in fact, been tried. The crust of dried sludge which forms at the top prevents the evaporation which assists to a considerable extent in the reduction of water. Openings in the crust permit the air to enter but a short distance. In consequence, the process of drying and also the nuisance of foul odors, which cannot be prevented by subsequent treatment with lime or peat, last for years. Only when natural pits exist, as at Leipzig, in the shape of an old river bed, and then at some remote point, can this method of drying be used. Moreover, the difficulty of conveying the de- watered sludge partly offsets any saving consequent to dispens- ing with an artificial drying place. Odors and the nuisance of flies may be considerably diminished by the means above mentioned so that the conditions are more tolerable for the employees at the plant. TREATMENT AND UTILIZATION OF SLUDGE 61 In general, however, it is preferable to remove the drying place from the plant when the neighboring land is occupied, unless a method to be described later be adopted, and to so locate it that it will not be a nuisance to the neighborhood. Land of little value can be used for this purpose and may be correspondingly extensive. Sludge conduits 3000 ft. (1 km.) or more in length have been used for this purpose in Germany. Closed pipes should be used preferably. In selecting a place the prevailing wind should be considered that it does not blow from the drying beds toward built-up areas. Drying beds for septic tanks do not require the same restric- tions, as there are no odors where the sludge is properly digested. The time required for drying, and consequently, to a certain extent, the size of the sludge beds, depends: 1. On the composition of the sludge. 2. On the character of the soil or the construction of the bottom of the basin. 3. On the atmospheric conditions. 4. On the method of operation of the sludge basin. The composition of the sludge, and in particular the amount of moisture contained, determine to a great degree the length of time necessary for drying. For example, 1.3 cu. yds. (1 cbm.) of sludge containing 95 per cent, moisture must have 198 gallons (750 1.) of the water removed before obtaining sludge with 80 per cent, moisture, as is found with septic tanks. A fine, greasy sludge gives up its moisture less readily, and under some circum- stances is very difficult to dry; while a thinner and less compact sludge has the opposite characteristic and gives up its moisture easily. The granular, fluid septic tank sludge, as well as that from lignite treatment, has this favorable quality. The de- posited sludge from the Kremer apparatus is easily de-watered as it contains so little grease. A basin with a porous base may be of less size than if compact. If the bottom does not promise free percolation it should be arranged as an artificial filter. Care should then be taken to clean or renew the covering layer frequently. As evaporation has a marked effect on the drying, this takes place more rapidly in summer. A sunny or windy location is also favorable to drying. To secure the best results drying should take place quickly on an ample area. The sludge should therefore be distributed in 62 SEWAGE SLUDGE thin layers about 6 to 10 in. (15 to 25 cm.). A rapid loss of water through the subsoil occurs, and the cracks caused by drying, plainly seen in Fig. 21, permit the air to pass to the underlying strata. Sludge shrinks in drying to from 2 to 3 to 1 to 2 its original volume. A fresh layer can then be admitted on the dried layer. Sometimes the sludge is dried directly in the settling tanks. These must then be thrown out of service for some time, as by this method evaporation does most of the work. The time used for drying lignite sludge in this way at Copenick is from 3 to 4 weeks. There is a project for the adoption of a similar method at Neustrelitz ("Mitteilung d. Kgl. Priif. Anstalt/ ; Vol. VI). The size of the necessary basins prevents its use where these are fixed or where there is insufficient land. Special beds for this purpose are always desirable on account of the greater rapidity of drying. Different intervals are required for drying, depending upon the different conditions mentioned above. As already stated, the septic tank combines the most favorable of these conditions. The length of time required for drying by the Emscher Associa- tion, e.g., averages 5 days with favorable weather only one or two days. Sludge taken from the septic tanks at Halberstadt at intervals of about 8 weeks requires 14 days for drying in good weather. In both cases it is received in thin layers. In contrast to these are those plants where sludge is delivered to the sludge basin to a depth of 2.3 to 3.3 ft. (0.7 to 1.0 m.). The process of drying here usually takes from 6 to 9 months. In general, normal settled sludge with about 90 per cent, water, requires some 6 or 8 weeks in summer and 6 months in cold weather. The size of sludge basins can be estimated from the amount accumulated daily and its average time for drying, allowing a certain time for the removal of the dried material. Both factors are subject to great variation with different processes and plants for reasons already given, so that an estimate based upon these figures would have no practical value. As a guide for the area required for drying, the following table, showing the size at different plants, is given; for a great nuisance may result, as has been shown by examples, where these are made too small, while too large an allowance results in too great a cost, especially in the neighborhood of high-priced city property. TREATMENT AND UTILIZATION OF SLUDGE 63 ^ tn 1 i .2 8 1 JS "3 If wells, reserve. JS 1 1 1 1 1 1 1 _ JS 1 imentation imentation imentation ich land in imentation imentation imentation imentation imentation 1 1 Q <*5 1 e M V cr o imentation npitation \v 1 B 1 1 1* 1 1 1 1 1 I 1 Pi 1 Q. 1 1 1 I B* 2 a s o g 3 s s 3 8 2 (N 00 | a t M C O , TJ H .2 >> 1 g g 00 g | s 3 CC S 2 g g 1 S g oo" t^ CO CO 03 fj 1 1 1 g OQ 49 ^2 ^ o 1 CO CO CO 1 1=3 99 CO S CO CO ffl O OB bC 1 bC g, ^s 3 S DC 1 CQ ^ fl i ? d 1 bC J | O -M cu A .9 CP C3 bC i, o i b 13 t p o o a i OH i |1 rvi P r ^ J *" ?S 1 8 i fi| I 1 " > . a a T c ^ oo a ill 13 1 ^ O -^ ^ t- g t* CO > , f s , _^_ _ ___ . _ "3 *e8 "^ d " " M M > M CN . ^ 5.55 i^ a 3 a w iSj3iO COCO O M M CM OS f .g O^^ tlf 13 5S 3 I U !; :l ; i I I 8 I I -5 T3 w ^-2 Jtj.Jij PJ> = liilirlfiiliil ^ slla llll.fi 158 SEWAGE SLUDGE Ir 1 o > f 55 i gs s* ^ ~ M 06 ^ . W 88 cj co o 2 o ^ ^1^1 ^a 1 2,1 t^ ^ 00 00 * DRYING OF SLUDGE 159 time no value; first, because it is not practicable to obtain large amounts of fresh sludge with much less than 90 per cent, mois- ture; secondly, because the draining beds become clogged after fresh sludge has been placed 6n them). As a rule also, it gives out an unbearable odor, noticeable at a long distance, after about 3 days. 3. Drainage water from fresh sludge becomes biologically pure after slowly percolating through the layer of slag, but still contains much organic matter in solution. B. Decomposed Sludge. The loss of water by draining de- composed sludge was 80.9 per cent, of the total loss of moisture, so that only 19.1 per cent, of that lost was evaporated. C. Comparison of Fresh and Decomposed Sludge. A com- parison by draining the two kinds of sludge shows that: 1. Fresh sludge takes much longer to become spadable than decomposed sludge, even when it is at first partly de-watered (33 as compared with 16). 2. Fresh sludge gives off much less drainage water than de- composed sludge, even when it contains more moisture (47.45 per cent, as compared with 55.7 per cent.). 3. "Drainage water from decomposed sludge contains less organic matter than from fresh sludge. 4. Decomposed sludge loses more organic matter by drainage than fresh sludge. DEDUCTIONS Provision should be made for drainage in constructing drying beds for decomposed sludge. The drain pipes should be large enough to furnish an unobstructed flow for the large amounts of effluent at the beginning. Drainage water from beds of fine slag requires no further treatment. It can be discharged into any stream. THE REASONS FOR FACILITY IN DRAINING The principal result of the experiments described was establish- ing the fact that decomposed sludge from Emscher tanks can be drained, i.e., it dries in a short time by parting with a large part of the water which disappears (to 80 per cent.) through the porous bed. It remains to find out what characteristics are required to render drainage easy. 160 SEWAGE SLUDGE Viscosity. The experiments with fresh and decomposed sludge furnished very important information. They showed that with a cover to the bed of uniform sized grains fresh sludge ran through, while decomposed sludge merely lost its moisture. The reason lies in the difference in concentration. With fresh sludge only the coarsest ingredients remain on the drainage surface at first, owing to its fluid state, due to the large amount of contained water, while the finer material in part penetrates to a greater or less depth into the covering layer, some of it passing all the way through. The layer becomes more dense by the accumulation of the particles of sludge which pene- trate the surface, no more passes through and at a certain depth an almost impenetrable mass is formed of the covering material and the particles of sludge which, when the second or third dose of sludge is applied may, under some circumstances, become so thick that it offers a strong resistance to the passage of water. There can then be no question of draining through so impervious a bed. The more concentrated septic sludge^ and the thick-flowing digested sludge of Emscher tanks, on the contrary, do not pass through the filtering layers, but give off their water. Destruction of Colloids. According to the results of the second experiment Emscher sludge drained more rapidly than artificially concentrated fresh sludge from the same plant. This is due largely to the fact that the colloids in the fresh sludge are partially destroyed (in digested sludge Trans.) . Presumably the decom- position caused by bacteria and enzymes which attack the organic material on the surface, is most apparent in the sponge-like hydrogels filled with liquid with their enormously large surfaces. The destruction of these diminishes their property of holding water. As the sludge loses moisture it drains more easily. Destruction of Organic Matter. The destruction of organic matter, such as fragments of animals and plants, which are found in the sewage from kitchen, garden and slaughter house wastes, takes place in the same way. These substances, which bind, and from the beginning contain, much water, are found only in very small quantities in decomposed sludge. The difference in the water content between fresh and decom- posed sludge shows how far the destruction of the water binding colloids and organic matter has progressed. As compared with 90 to 95 per cent, moisture in fresh sludge, I found, e.g., in DRYING OF SLUDGE 161 Emscher sludge from the Recklinghausen plant an average of 79.3 per cent., in sludge from the Essen-N. W. plant only 75.6 per cent. Occasionally liquid sludge is obtained from- Emscher tanks with nearly as little as 70 per cent, moisture, a concentra- tion equal to the spadable sludge from centrifugal machines. On the 8th of April, 1909, in an average sample of 123.58 cu. yds. (94.34 cbm.) of wet sludge drawn off under water, from the Essen-N. W. plant, e.g., I found 71.9 per cent, moisture; from another taken May 8, 1909, of 85.1 cu. yds. (65.0 cbm.), 71.35 per cent, moisture, while, according to examinations made at the Royal Experimental Station for Water Supply and Sewage Disposal 1 , the spadable centrifuged sludge from Harburg con- tained between 69.7 and 74.2 per cent, moisture, an average of 72.5 per cent. A sample taken by me at Harburg in 1908 showed 68.8 per cent. In Frankfort the fresh centrifuged sludge contained about 70 per cent, moisture (according to data fur- nished me there in 1908). The destruction of water binding substances is shown also when in a spadable condition. Thus I found in 4 samples of Emscher sludge at Reckling- hausen-Ost which had just become spadable, an average of 58.27 per cent., in 13 samples from Essen-N. W. an average of 52.34 per cent. We may thus assume for spadable fresh sludge about 71 per cent, moisture, for spadable decomposed sludge about 55 per cent. Gas Contained. The ability of decomposed sludge to drain is materially assisted by the gas contained. As already mentioned, large quantities of gas are formed by the decomposition of sludge in Emscher tanks, which consists mainly (about 3/4) of methane and (about 1/4) of carbonic acid. These gases pass off as soon as large bubbles are formed from the original minute ones, as the former overcome the pressure of the overlying layer of sludge. A large volume of gas at one point is necessary to effect this. The bubbles remain in the viscous material until this occurs. At the greatest depth, about 33 ft. (10 m.) the gases are under a pressure of one atmosphere. If sludge is drawn off it comes filled with compressed gas. With the release of pressure from this greater depth the volume of the bubbles increases, increasing 1 Reichle and Thiesing "Mitteilung aua der Kgl. Pruf-Anst. fur Wasserv. und Abwasser- beseitigung," No. 10. 11 162 SEWAGE SLUDGE the volume of the sludge. This, being full of these gas bubbles, is changed into a foaming mass. The increase in volume renders drainage more easy. The tendency to penetrate the surface layer of the beds is reduced. The water in the sludge passes through the channels formed by the disappearing gas, seeps down and drains off. If sludge freshly drawn from an Emscher tank is allowed to stand in a glass cylinder (which may be con- sidered an impervious sludge bed) bubbles of gas may be seen on the sides which gradually increase in number and size. The volume then increases and a layer of clear water forms at the bottom. The volume of sludge above the water is not reduced as FIG. 33. FIG. 34. FIG. 35. it has a foamy structure, i.e., it contains a great number of small and large compartments filled with gas bubbles. This foamy material, being lighter than water, is forced up by the water which settles to the bottom. It also spreads as the gas increases in volume. The volume of the whole is thus increased by more than that of the water at the bottom. Figs. 33 and 34 illustrate the process. The original height of the sludge is indicated by the upper edge of the strip of paper. The second cylinder shows how the water has settled after 24 hours and the entire volume is increased. The thin layer of sludge at the bottom is composed of heavy particles which are deposited later, as shown by the solid particles just sinking. DRYING OF SLUDGE 163 This method increases the ease of drainage appreciably. The water can filter through unhindered as it reaches the porous cover- ing containing no sludge. Fresh sludge is just the reverse in this respect. The water does not sink, but rises. Fig. 35 represents fresh sludge from the clarification plant at Essen. 24 hours after being placed in the cylinder. The upper edge of the paper indicates again the orig- inal surface of the sludge. It can be seen that the sludge has not risen and that dirty water is on the top. In order to show to what extent the enclosed gases cause these phenomena in decomposed sludge and whether a subse- quent evolution of gas assists, I experimented with a sample of sludge from Essen-N. W. by warming a portion of it for two hours at 99 F. (37 C.) , and stirring it frequently to remove the larger gas bubbles and then removing the gas as much as possible by subjecting it to the vacuum produced by a good ejector while shaking it frequently. The sludge sample so treated and an- other without having the gas removed were allowed to stand 24 hours with as uniform a temperature as possible. The original amount and the increase in volume and the set- tled water were measured. TABLE IX SLUDGE FROM TANK No. 5 OF THE EssEN-N. W. PLANT 1. In original condition 2. With gas removed Gals. c.c. Gals. c.c. Quantity at beginning of 0.1096 415 1 0.0832 315 experiment. After 24 hours 1 O 1 4OO 530 0937 3552 Increase in volume 0.0304 115 0.0105 40 Same in per cent, of 1 original amount J 27.7 below. 12.7 above. Water separated 0.0105 40 0.0040 15 Same in per cent, of ) original amount. / 9.64 4.76 3 The temperature at the beginning was 60.8 F. (16.0 C.) and at the end 59.9 F. (15.5 C.). 1 425 in original. 2 455 in original. 3 4 . 3 in original. The foregoing alterations made to secure consistent results as the original figures are erroneous. Tr. 164 SEWAGE SLUDGE It is an astonishing fact that in spite of the gas removed there was a perceptible increase in volume, although this was not quite half so large as before. It is possible, either that the gas was not entirely removed and that a thicker more watery layer had accumulated in the lower part of the sludge, forcing up the lighter parts, or else that, on account of the action of bacteria and enzymes on the sludge, there was a further development of gas, thus increasing the volume. Probably both these views are true. EXPERIENCE IN METHODS OF DRAINING AT LARGE PLANTS These experiments show that with proper preliminary treat- ment (decomposition under water in deep tanks) sludge on drained drying beds may be easily separated into a spadable earthy material and a harmless liquid which has the character- istics of an effluent from contact beds. These experiments, although successful on a small scale, do not solve the question as to the applicability of this method to a large plant. Drying sludge by draining has been practised on a large scale at Recklinghausen-Ost (28,000 inhabitants), Essen-N. W. (60,000 inhabitants) and Bochum (130,000 inhabitants), as well as at several smaller plants. The results have been much more favorable than was anticipated. Much material is available regarding the results of drying at the more accessible of the two large plants, that at Essen-N. W., collected by operating engineer Blunk, in so far as it relates to the measurement of the depth of sludge and the time of drying, in connecteon with estimates for the contractors for the removal of the sludge authorized by the Emscher Association. These measurements have been shown in diagrams (not reproduced). The rainfall was measured by Mr. Winter, Municipal Superintendent of Clarification, at the Essen plant. Description of Drying Beds. The drying bed at Essen-N. W. for sludge taken from a tank 29.5 ft. (9 m.) deep lies several meters below the surface of the ground and is artificially drained by an underground conduit laid parallel with the stream to which it empties, and has an outlet below a dam. The bed is supplied with drain pipes laid end to end, at intervals of 8.2 to 9.8 ft. (2.5 to 3 m.). These lead to an open ditch surrounding the bed. Above the pipes is a layer of furnace slag 12 in. (30 cm.) thick, and above this a layer of crushed slag 8-10 in. (2 cm.) DRYING OF SLUDGE 165 thick. (Coke cinders are sometimes used in place of the latter, as they are often cheaper). In recent plants having a sand catcher the grit taken from this is used. As this contains no floating particles it need only be placed in thin layers. The drying bed is divided longitudinally by planks into 3 parts, numbered I, II and III. They are 3465, 3411 and 3153 sq. ft. (322, 317, and 293 sq. m.) in size. Each has, along the middle, rails supported by piles for carrying the sludge away. The plant began operation in December, 1908. Sludge was placed on beds I and III April 8, 1909, and on bed II April 10, 1909. In a short time (3 to 5 days) it became spadable, but was not removed from the beds until April 19, 1909. (Time of retention 9 to 11 days.) NOTE BY TRANSLATOR In the conclusions drawn from these experiments no con- sideration has been given to these first drainings, as it could not be determined definitely when the sludge became spadable. The results that were reached cover the period of a full year, ending May 1, 1910. The septic sludge received by the drying beds was as follows: Month, 1909 Bed number I II III Total Cu. yds. Cbm. Cu. yds. Cbm. Cu. yds. Cbm. Cu. yds. Cbm. May June July August 355.3 358.1 271.7 278.1 271.6 273.8 207.7 212.6 424.1 264.8 201.2 337.2 324.2 202.4 153.8 257.8 360.4 337.3 175.5 326.5 275.5 257.9 134.2 249.6 1139.8 960.2 648.4 941.8 871.3 734.1 495.7 720.0 The total for June, July and August was about 2550 cu. yds. (1950 cbm.) in 92 days, giving an average of 27.7 cu. yds. (21.2 cbm.) of septic sludge per day containing about 80 per cent, moisture. According to Spillner and Blunk 1 the mean daily flow of sewage to the Essen-N. W. plant was, at the time under con- sideration (1909-10), as follows: 1 Tech. Semeind., Vol. XIII (1910). 166 SEWAGE SLUDGE Sewage from 60,000 persons ... 2.77J mil. gal. = 10,500 cbm. =32.0% Wastes from Krupp's works ... 9.51 mil. gal. =36,000 cbm. =63.7% Mine drainage 0.26| mil. gal.= 1000 cbm. \ _ Coal washing water 0. 13 mil. gal. = 500 cbm. / = Total 1 12.68~ mil. gal. =48,000 cbm. = 100. 0% If we assume this volume equivalent to that derived from a population of 65,000, we have: Volume of sewage per capita daily 194.8 gallons =738 lit. Volume of wet sludge per thousand persons daily 426 cu. yds. = .326 cbm. Volume of wet sludge per million gallons sewage 2.19 cu. yds. Volume of wet sludge per cubic meter sewage, = . 442 lit. The results of operation show that the expectations from the methods adopted for drainage have been realized. In spite of an unusually wet year, sludge averaging 9 in. (23 cm.) in depth, became spadable in 5.87 days. Sometimes, in^dry weather, it dried in 2 days, as May 11 (III) and May 20 (II); in September sometimes in one day. In the 365 days under consideration, the drying beds were: I Occupied 236 days Empty 129 days. II Occupied 246 days Empty 119 days. Ill Occupied 294 days Empty 81 days. These figures show that the beds were not completely utilized although their area was but about 9684 sq. ft. (900 sq. m.), making, for a population of 60,000, only 0.161 sq. ft. (0.015 sq. m.) per capita. The tables show, moreover, that sludge is seldom removed in winter. As it takes longer to decompose and to dry in winter than in summer, care was taken to provide as much storage capacity as possible in the deep sludge chambers in winter. In this way one is independent of the weather, as it is only necessary to discharge small quantities of sludge, and these at long intervals. Table X shows the changes which sludge undergoes in drain- ing. The amount was reduced 45 to 58 per cent, in weight, 60 to 77 per cent, in moisture and 0.1 to 0.9 per cent, in dried material. 1 The Krupp wastes contain the sewage and water used in lavatories from about 10,000 workmen. The sewers are on the combined system. The disposal works consist of two grit chambers, one coarse screen and nine Emscher tanks. These were built in 1907-8 and put in operation November, 1908. DRYING OF SLUDGE 167 S S n a 03 3 VO +S -2 -*-3 S -f^ o Q I I d C^ t^ rH 00 * CO r-I r-! g 8S TH' ^ do CO (N C^J (N O) d do . '.Jj ^ I* 5 * ^ . ~*~. t> 00 iM 00 i f CO & CO ^ 05 b\ 9 > 00 00 00 CO rH CD O CO rH S 00 t- 05 05 1 i CO t^ rH 1C co' O5 5 CO CO CO rH r>. (N 00 CO CO CO " S 1 -2 - 3 -rS ^ *3 ^ ^ gj 1 ^ o CN rH ^ h* N. ^* CD CO 1C rH 1C C^ j I O O O5 CD C 05 00 rH t- ^ oo i> CO (M rH < l-~ 00 CO* ci N CD d rH CO 00 t^ (N ic oo Tt< 1C CO CO CO 10 1H * "* CO 10 <* * * CO CO 1 ^ 2 " n L SS ^ L 'i 1 55 S CO oo S co CO O O rH O5 rH O rH CO 5^ O5 00 CO CO (M "S " 9 - 910 3 ^ * o ooo CO 00 t- t>- O O5 a DO i .2 I *J 1 4i 1^ 1 ^ 1 +5 T3 fj ^\ Q fcj^ d SCN 1C rH (N ^- oo t>- (N CO O5 ^h rH rH C H/l rH CO 1C (N b- 00 t>. 00 O O5 CO CM CO t^ CO (N rH 1C rH l-H rH TH 1C TH rH S CO I'J jL. -2 *j J-^ s- CO rH CD I ^ Oi ^ ^ CO n . <. ij5 ^ ^ O5 00 1C | rH 71 i-H t 1 ^ 1C I s - C CO 1C rH O5 CN rH rH (M rH rH (M <* sO l> 00 rH CD O5 ^ l> O Oi N CO N oo * TH~ ^1 {2 00 -H CO s ss 8 SS rH CO O5 00 CO >O Tt< (M 1C t^ CD C L 1 s I lagj ti- n +3 O oi r O5 CO ^J uj t^ CO ^ O5 i-l ^H ^ CO (N QQ 1 1 . *"! s, "co'^ r ^ oo i> r>> M 4^" ^j^ r r oo t> * d co' d CO 0) CD C O ^ r^ c5 CO ^ JQ ^ c5 l> s^ CO 00 00 00 sl 5 6 ,a I-H" .g s* & a rH o< 05 Q- . g Q . g' o d a o a O rH .S CJ . O -.So n3 .as I-H" '^ ^ rH rrt 11 ^ O -d ^ f* HH CO * B CO t^ t> 05 PQ rH 0) GO O 11 2 "S . o" CQ Q M 2 co" cf 1 | 0) 3 r- t i 'C - P a r a C 00 OS CO ^5 3 ^ ^ ^ ^' 3 *; $ 3 2 S J-H rH rh 00 "^ "^ OS CO rH CO OS CO rn" ^ 00 ) rH rH t^ ^ - co ** (N rH 3 22 s? as d 3 ; j^ ' d : 1 ^ ! ! .^ O a : oo (M CO co os '. % S : o ^ : 2 : 88 CO M : ^" ;, C^C^ : "^ S '. M . d :'B ; d : b :| : b ! bC I r t T3 -o -c - T3 3 * * s? j|! 2 o >> i.if 2"o | ii- d I a ^ -o o o t; a ^ - ^ a v J2 O t) . a ^ -D b 1 a CO - O CO co os CO 01 rH rH * CO ?q 2 2 " "1 a a a 'J a d B . .3 | .a | 00 p (M >O t. ^ 1C IM -* os .0 b- O CO 2500 | 2250 _; 200O u 1750 . 1500 X 1250 \ 000 750 O 5OO 250 / ^ / \ / f ^ * f - ."' J f f j / s ., f ^ ^ , ^ * / -' , * ' . -* - - ' s_ 4 1 -I: i 4 ,8 5 I f ^ $ 1 I -* 1 & .0 & i 2 1 ^ -= -= 1 $ ^ *& . -------- J907- ...... ->< - -I908- 1909 ....... - FIG. 36. Diagram showing increase of sludge in the Recklinghausen-Ost Clarification Plant. The upper line represents the aggregate volume of sludge deposited and the lower line represents the aggregate volume of sludge discharged. been 1910 cu. yds. (1460 cbm.) ; hence on this day the aggregate discharge was 1910 + 59 = 1969 cu. yds. (1505 cbm.). By moving this ordinate to the left until it intersects the upper line representing the total sludge deposited, it will be found that this intersection corresponds on the axis of abscissas to Oct. 17, 1908, thus indicating that the sludge which was removed on April 20, 1909, had remained in the tank for a period of six months. In reality, however, the period of detention in the tank is considerably less, as the sludge does not descend or move at a uniform rate from the surface to the mouth of the discharge pipe in the sump at the bottom of the tank. SEWAGE CLARIFICATION PLANTS 175 Before and after any sludge is discharged from a tank, the position of its surface is always carefully noted by soundings, as above described. The difference between these two measure- ments gives the quantity removed, which is checked by measur- ing the depth of the mass at a number of places upon the level drying bed or filter. If made quickly, or before an appreciable quantity of water escapes into the underdrains of the bed, the two measurements agree closely. The amount of water in the discharged sludge varies with the depth of the tank and the age and chemical composition of the sludge. As will be shown subsequently, it contains on the average about 75 per cent, of water as it leaves the tank; and after being allowed to drain for a few days upon the drying beds, the quantity of moisture reduces to 52 per cent, at Essen N. W. and 65 per cent, at Recklinghausen, or to 58 per cent, on the average. By this drainage the volume of the sludge is reduced about 40 per cent., and it then becomes consistent enough to be spadable, or to be cut and handled with a shovel The authors exhibit in diagram form the results attained with the sludge of the Essen-N. W. plant for the year from April 1, 1909, to April 1, 1910. There are three separate sludge draining beds, and the observations relating to them during this period are shown graphically. The several lines indicate the date and quantity of sludge discharged, and the subsequent date and volume when the sludge had become spadable and was removed from the drying bed; also the depth of the rainfall and the date of its occurrence. When first taken from the tanks the sludge contained from 72 to 75 per cent, water, and when finally carried away from the beds it contained from 55 to 60 per cent, water. The abscissas indicate the number of days required for the sludge to become dry enough to handle with a shovel. Thus on October 6, 1909, 95.6 cu. yds. (73 cbm.) of liquid sludge was discharged upon bed No. I, and only three days later it was found to be spadable, its volume having reduced to 53.1 cu. yds. (40.5 cbm.). In this short period the shrinkage in volume was 42.5 cu. yds. (32.5 cbm.) or 44.5 per cent. Another diagram shows the accumulated volumes of liquid and drained sludge during the twelve months mentioned, each by a continuous line or curve. It shows that during this time 7194 cu. yds. (5500 cbm.) of liquid sludge had been discharged from the tanks, and that this volume had been reduced by drainage 176 SEWAGE SLUDGE to 4709 cu. yds. (3600 cbm.), thus making the average shrinkage in volume 35 per cent. The preceeding diagrams also indicate a large variation in the time required for the sludge to become spadable, but the reason therefor becomes evident on comparing these periods with the corresponding rainfall. Thus on July 13 and 14, 1909, all of the beds had been filled with sludge, and in the afternoon of the fourteenth, an excessive rainfall occurred that yielded a depth of 1.34 in., and by the failure of an embank- ment caused the sludge beds to become covered with water to a depth of 8 in. In consequence of this accident the sludge in one of the beds did not become spadable until July 27, a period of 14 days, although a much shorter time sufficed in the other beds. Such cases, however, are exceptional, and the average period, including rainy weather, is from 6 to 7 days. In dry summer weather, the drainage or drying is frequently accomplished in two or three days, while in severe winter weather a somewhat longer time is required, as the water in the sludge may then freeze. This freezing is troublesome, as the sludge after thawing is not only rendered nearly as wet as it was originally, but is also deprived of its contents of gases upon which the facility for quick drainage depends in high degree. This peculiar property was fully pointed out in a paper by Dr. Imhoff, in Technisches Gemeindeblatt, October 5, 1910, pp. 193-199. In consequence of the escape of the gases while the frozen mass is thawing, the wet sludge settles upon the surface of the bed, theje- by causing it to become clogged and compelling the water to rise to the top of the liquid mass, as in the case of freshly deposited sludge. For this reason it becomes expedient to discharge but little sludge in winter, and to make the utmost use of the storage capacity in the septic chambers of the deep tanks by withdrawing therefrom as much sludge as possible while the weather is favor- able in the summer and autumn. The sludge beds of the Essen-N. W. plant have an area of 1077 sq. yds., and in the said period of twelve months they drained a volume of 5500 cbm., or 7195 cu. yds., of liquid sludge. This is at the rate of 6.68 cu. yds. per square yard of surface per year, which represents a depth of 20.04 ft. on the entire surface. The liquid sludge was deposited on the beds to a depth of from 8 to 10 in. at each application, thus requiring about 27 or 28 applications per year in order to drain the stated volume; and as the average period of time required for drainage is about 6 days to each SEWAGE CLARIFICATION PLANTS 177 application, it follows that the sludge beds must be in active use for an aggregate of 6X28 = 168 days per year. This computa- tion shows that in the climate of Essen ample time is available during the year for the repeated fillings, clearings and repairs of the sludge beds after due allowance for freezing weather in winter. At all the other plants of the Emscher Association, the experi- ence with the sewage sludge is similar to that at Essen-N. W., as described above. It should also be mentioned that at Reck- linghausen, Holzwickede and the colony at the Count Schwerin Mine, the drained sludge is taken away by neighboring farmers, while at Essen and Bochum, where little agriculture is carried on, it must be used for filling depressions and low places. [The populations tributary to the Recklinghausen, Holzwickede and mine colony plants are respectively 30,000, 3200 and 3100, while those tributary to the Essen-N. W. and Bochum plants are respectively 60,000 and 145,000. The aggregate dry- weather flow of sewage at the first three plants is about 2,460,000 U. S. gallons per day, while at the last two plants it is about 25,910,000 U. S. gallons per day and contains much mine drainage and ground water. The quantities of sludge produced annually at each plant are not given, but it is obvious that only a small proportion of the drained sludge finds agricultural utilization. Trans.] It is of much interest to compare the volume of the fresh sludge, as it is deposited in the settling chamber or upper portion of an Emscher tank, with that of the decomposed liquid sludge dis- charged from the bottom of the septic chamber, and also to determine how much of the original volume is left after the septic sludge has been drained or dried until it attains a consistency like that of moist earth which can be cut and handled with a shovel. Let us assume that the fresh sludge contains 95 per cent, water. After remaining for several weeks in the septic chamber, it will contain only 75 per cent, water, .and about one- third of the original quantity of organic matter will have been gasified. In 100 cbm. of fresh sludge there will accordingly be 5 cbm. of dry solid matter, of which 65 per cent, on the average, or 3.25 cbm., will be organic matter. Since one-third of this latter substance, or 1.08 cbm., becomes gasified, the remainder will be (3.251.08) =2.17 cbm. of organic matter. The mineral matter amounts to 5X0.35 = 1.75 cbm., and hence the original 12 178 SEWAGE SLUDGE volume of 5 cbm. of dry solid matter is reduced to (2.17 + 1.75) = 3.92 cbm., of which 55 per cent, is organic and 45 per cent, mineral matter. The septic sludge, however, contains 75 per cent, water; hence with this addition of water the 3.92 cbm. of resultant dry solid matter will have a volume of 3.92x4 = 15.68 cbm. The original volume of 100 cbm. of fresh sludge has thus reduced to a volume of 15.7 cbm. of the liquid septic sludge yielded by an Emscher tank. This represents a shrinkage in volume of about 84 per cent. Furthermore, this liquid septic sludge shrinks about 40 per cent, in volume by drainage upon the beds to a spadable con- sistency. Its volume in the aforesaid case is thus reduced to 15.7X0.6 = 9.4 cbm., and hence we have a total reduction in volume of (1009.4) =90.6 cbm., or nearly 91 per cent., of the original volume of 100 cbm. of freshly deposited sludge. EXAMINATION OF THE LIQUID SLUDGE The data given in the tables refer to average samples of the sludge. In collecting samples for examination, a small portion of the liquid is taken at regular intervals during the period of discharge as it flows in the open trough on its way to the sludge bed, and by mixing together all these portions an average sample is obtained. These average samples are placed in tightly closed jars and brought to the laboratory, where they are usually examined on the same day. The examination generally em- braces the following determinations: 1. The external peculiari- ties and smell; 2. the amounts of contained water and dry* matter; 3. the proportions of organic and mineral substance in the dry matter; 4. amount of total nitrogen in the dry matter; 5. reaction, alkaline or acid; 6. amount of fat in the dry matter; 7. amount of gas-making matter and fixed carbon, by coking; 8. amount of silica, iron and alumina in the ash. The results of a number of such sludge analyses are given on pages of Spillner's paper on "The Drying of Sludge." These data are now supplemented by the tables given in the present paper. The sludge that is decomposed in the deep Emscher tanks is very black in color, and has the consistency of a more or less thick gruel. It is usually quite liquid, and flows easily in a trough. In this state it is difficult for the unaided eye to SEW AGE CLARIFICATION PLANTS 179 recognize the nature of its various components. Its reaction is always slightly alkaline. It has a faint odor of india-rubber or tar, even in localities where the liquid wastes of coke and gas works are not admitted into the sewers. This tarry odor is due to the activity of certain micro-organisms, and is also found in well-decomposed river mud and the sludge from other well- ripened septic tanks. It is always faint, and can be detected only in the immediate vicinity of the mass; hence it cannot pollute the atmosphere sufficiently to be regarded as a nuisance if the sludge is properly decomposed. Every Emscher or other septic tank, however, requires a certain period of time after being placed in service before its operation becomes satisfactory, and therefore it may happen that a serious nuisance will arise if the sludge is discharged too early upon the drainage beds. Such a condition occurred at two of our plants, Recklinghausen and Bochum, before we had learned by experience how to prevent it; but after they had been in operation a sufficient length of time the development of all disagreeable odors ceased. If it becomes necessary for any reason to discharge undecomposed sludge dur- ing this ripening period, the material should be treated like other freshly deposited sludge, such as quick burial in the ground. The large amount of gas contained in Emscher tank sludge, 75 per cent, of which is methane (CH 4 ), and therefore combustible, and 25 per cent, carbonic acid (CO 2 ) , has already been mentioned in Spillner's earlier paper. These gases also contain traces of hydrogen, nitrogen, ammonia and sulphuretted hydrogen. The part played by these gases in rendering the sludge mobile and in facilitating its drainage and drying has also been explained. The specific gravity of the sludge obviously varies with the amount of gas present. This is demonstrated by the fact that from time to time large quantities of sludge will detach them- selves from the bottom of every septic tank and rise to the sur- face of the liquid, where they discharge their contents of gas and then sink again to the bottom. Sludge that is free of gas has a specific gravity of 1.09 to 1.22. Details of analyses are given in the following. Tables I, II and III, relating to the Recklinghausen, Essen and Bochum plants. In regard to the analyses at Recklinghausen, it should be remarked that since the end of 1908 this sludge cannot be con- sidered as normal Emscher tank sludge, because the capacity of the plant has been greatly exceeded by the unexpectedly 180 SEWAGE SLUDGE rapid increase in the quantity of sewage, and hence the time required for a thorough decomposition of the sludge is no longer available. The quality of the sludge, moreover, is different from what it was formerly. No bad results, however, have yet appeared, as the change in quality is manifested only by the larger water content of the sludge, and the longer time required for its drainage on the beds; but it does not become putrid in drying, which is the main thing to be attained. It is intended to relieve the tanks to some extent by first passing the sewage through a detritus chamber which will extract the sand and other heavy matter. The rapid increase in the quantity of sewage from the other cities will also affect the remaining plants by reducing the time available for the decomposition of the sludge. Table I gives 30 analyses of liquid sludge from the 6 Emscher tanks of the Recklinghausen plant, taken on 15 different days between June 14, 1907, and September 2, 1910, three or four analyses of the same date often relating to the sludge from different tanks; the depth of the tanks is not stated. The essential figures are as follows: TABLE I ANALYSES OF EMSCHER TANK SLUDGE. RECKLINGHAUSEN Max. Min. Average Water content per cent 88.3 75.0 82.9 Dry matter, per cent Mineral component of dry matter, per cent 25.0 64.4 11.7 40.8 17.1 54.7 59 2 35 6 45.3 Nitrogen component of dry matter Fat component of dry matter, per , per cent cent 3.64 10.79 1.18 5.17 1.74 6.87 Table II gives 16 analyses of liquid sludge from the 9 Emscher tanks of the Essen-N. W. plant, taken on 15 different days between April 4 and October 11, 1909; 6 of these analyses refer to either mixtures or averages from 2 or 3 tanks. All these tanks are 9 m. = 29.5 ft. deep. The essential figures are as follows: SEWAGE CLARIFICATION PLANTS 181 TABLE II ANALYSES OF EMSCHER TANK SLUDGE. ESSEN Max. .Min. Average 81.8 71.3 75.6 28.7 18.2 24.4 Miiionl component of dry matter per cent. . ; 53.5 37.6 45.1 Organic component of dry matter, per cent 62.4 46.5 54.9 1 43 1 02 1 22 Fat comnonent of drv matter, ner cent . . 7.36 3.44 4.95 Table III gives 24 analyses of liquid sludge from the 18 Emscher tanks of the Bochum plant, taken on 11 different days between February 11, 1909, and December 13, 1910. All of these analyses refer to single tanks; the depth of the tanks is not stated. The essential figures are as follows: TABLE III ANALYSES OF EMSCHER TANK SLUDGE. BOCHUM Max. Min. Average Water content per cent . 83.9 70 9 78 1 Dry matter, per cent Mineral component of dry matter, per cent Organic component of dry matter, per cent Nitrogen component of dry matter, per cent Fat component of dry matter, per cent 29.1 71.5 50.7 1.50 12.30 16.1 49.3 28.5 0.87 3.53 21.9 61.9 38.1 1.18 6.12 It has been observed that the water content of the sludge depends in high degree on the depth of its surface (as determined by sounding in the manner described in the foregoing) below the surface of the water in the tank, and also upon the age of the sludge. If a tank contains only a small quantity of sludge, the presumption is that the sludge was deposited quite recently and that it will contain a relatively high percentage of water. This is always the case in our tanks at the end of summer, as they are operated so as to discharge as much sludge as can possibly be dried during the warm season, and thus make room in the tanks for the accumulation of sludge during the frosty days when it cannot be discharged upon the drainage beds. On the other hand, if the septic chambers are filled to a high level as 182 SEWAGE SLUDGE will be the case in plants of sufficient capacity to hold the sludge accumulations of from 2 to 4 months, the sludge will contain a very low percentage of water. The normal low percentage at the Bochum and Essen plants is about 73 per cent. The easy separation of the liquid sludge into water and a spadable mass is explained not only by the action of the gases already mentioned, but also by the fact that the organic matter has undergone an extensive decomposition. Unfortunately a measure for this decomposition cannot be deduced from the available analyses, as the data are not sufficiently complete to admit of a comparison with the composition of the fresh sludge; but other investigations are now in progress from which it will be possible to make such a comparison. We can, however, form a rough estimate of the extent of the sludge destruction or digestion by considering the volume of the gases produced. Several measurements of this volume were made at Essen-N. W., and it was found that the plant yielded from 24,700 to 31,800 cu. ft. (700 to 900 cbm.) of gases per day. The weight of such gas is about (1.6855 Ibs. per cubic yard, or 0.0624 Ibs. per cubic foot) (1 kg. per cbm.), and hence from 1540 to 1980 Ibs. (700 to 900 kg.) of organic matter in the sludge were gasified every day. The records show that during that period the average daily produc- tion of decomposed liquid sludge was 18.31 cu. yds. (14 cbm.), of which 24 per cent, was dry matter; and as the specific gravity of the sludge is approximately 1.00, the daily yield of dry matter was accordingly 4.39 cu. yds. (3.36 cbm.) or 7407.5 Ibs. (3360 kg.), of which about 55 per cent, or 4078.5 Ibs. (1850 kg.) is of organic nature. Let us now assume that the loss or de- struction of organic matter in the sludge takes place exclusively by gasification, as we do not yet know the proportion thereof that is lost by becoming liquefied; this daily loss will then be represented by the aforesaid weight of 1540 to 1980 Ibs. (700 to 900 kg.), or 1763.7 Ibs. (800 kg.) on the average, of gas produced every day by the tanks. By adding this loss to the aforesaid residual organic matter in the decomposed liquid sludge, we will have for the daily quantity of organic matter that reaches the tanks: 4078.5 + 1763.7 = 5842.2 Ibs. (1850 + 800 = 2650 kg.). From this computation it is seen that about one-third of the organic matter contained in the fresh sludge is lost or destroyed by gasification. [Provided that no liquefaction occurs. It should also be remembered that these figures cannot be checked SEWAGE CLARIFICATION PLANTS 183 by the actual amount of organic matter in the freshly deposited sludge, which was not ascertained. Trans.] The foregoing figures cannot be regarded as being generally correct, as they relate to only one plant and a few measurements of the gas there evolved. They afford, however, some means of estimating how much sludge is lost by gasification in a properly working Emscher tank located in our climate. Reference may also be made to the experiments of Favre and Spillner for deter- mining in another manner the loss of sludge by decomposition in a septic tank, published in Gesundheitsingenieur, 1907, p. 810 and 1909, p. 825, respectively. The septic liquid sludge is a watery mixture of mineral and partly decomposed organic matter. On evaporation, the resulting dry matter has usually a gray color, but sometimes it is brownish-gray. It has little odor, and that which is devel- oped when heated to 212 F. usually resembles the odor of peptone. In most cases it contains few recognizable materials, but when such are found they are commonly bristles, hair^, stems of grains, small twigs, scraps of leather, sand, small stones, and fragments of coal; bits of tinfoil, card-board, wood and lime, and fish-scales have also been found therein repeatedly. The determination of the total amount of nitrogen in the dry sludge is made regularly, in view of the utilization of this material as a fertilizer at some of the plants. The resulting figures have exceeded our expectations, the averages being 1.22 per cent, at Essen-N. W., 1.39 per cent, at Bochum, and 1.57 per cent, at Rechlinghausen. All of the spadable sludge produced at the latter plant has been sold for fertilizing pur- poses, and good results have been attained therewith. Many determinations of the amount of fat in the dry sludge were made, but it was found that it was considerably less than that of the fresh sludge in other cities. Thus from 16 to 17 per cent, of fat was obtained from the dry matter of the fresh sludge at Frankfort, 18 per cent, at Liittich, 15 per cent, at Cassel and 14 per cent, at Harburg, while the amount obtained from the dried sludge of the typical -Emscher tanks at Essen-N. W. and Bochum was only from 3 to 7 per cent, in most cases. The difference must be ascribed to the decomposition attained in the latter plants. Inasmuch as the recovery of this fat has never proved profitable in other localities, it seems hopeless to attempt such a process where Emscher tanks are used. 184 SEWAGE SLUDGE Excepting the small proportion that is used as fertilizer, the bulk of the drained sludge produced by the plants of the Emscher Assocation is used at the present time for filling depressions and low places. In regard to the mineral matter of the dry sludge, a number of determinations of its principal components were made. The averages found at Essen-N. W. are: SiO 2 , 63.29 per cent.; Fe 2 O 3 , 11.37 per cent.; A1 2 O 3 , 6.56 per cent. It thus appears that the mineral matter in the sludge consists chiefly of sand. EXAMINATIONS OF THE DRAINED SLUDGE The sludge is described as "spadable" when it can be cut and handled with shovels on the drainage beds like moist earth, and be loaded into the tram-cars provided for its transportation to other localities. For the purpose of examination a number of samples, depending on the size of the drainage bed, are collected from different points and are then mixed together; the mixture is regarded as representing an average sample of the material, and is then placed in an air-tight receptacle and taken to the laboratory. The examination is made in the same manner as in the case of the liquid sludge. The surface of the spadable sludge has usually a grayish-brown color, while the remainder of the mass is mostly black. Its consistence varies from doughy to crumbly, according to the amount of moisture present, which in turn depends on the state of the weather and the length of time allowed for drainage. In structure, the spadable sludge from Emscher tanks is invariably somewhat spongy. On breaking an air-dried sample, the ruptured surfaces exhibit numerous small cavities and passages penetrating the entire mass, which were formed by the bubbles of gas contained in the liquid sludge, and obviously facilitate both drainage and subsequent drying in high degree. As the collection of a fairly representative sample of a large mass of partly dry sludge is a matter of considerable difficulty, the examinations of spadable sludge have not been as numerous as those of the liquid sludge. Table IV gives the results of 13 examinations of spadable sludge at the Essen-N. W. plant, on 11 different days between April 19 and August 28, 1909; and with periods of drainage ranging from 11 to 3 days. The essential figures are as follows: SEWAGE CLARIFICATION PLANTS 185 TABLE IV ANALYSES OF SPADABLE EMSCHER TANK SLUDGE. EssEN-N. W. Max. Min. Average 59 9 47 7 52 3 52 3 40 1 47.7 Mineral component of dry matter per cent 54 2 40 6 46.6 Organic component of dry matter, per cent 59.4 45.8 53.4 Nitrogen component of dry matter, per cent 1.40 1.01 1.17 Fat component of dry matter, per cent Drainage period, number of days 3.91 11 3.02 3 3.39 7 The results of 5 examinations of both the liquid sludge and the resulting spadable sludge at the Essen-N. W. plant, on the same number of days between May 25 and August 7, 1909, is given in Table X of Spillner's paper, pages 167 and 168. The averages of the results found from the examinations (number not stated) of spadable sludge at the Bochum plant during the fiscal year 19101911 are: Water content, 63.3 per cent.; dry matter, 36.7 per cent.; mineral component of dry matter, 64.4 per cent.; organic com- ponent of dry matter, 35.6 per cent.; nitrogen, 1.24 per cent.; fat, 6.91 per cent. Table V gives the results of 21 examinations of spadable sludge at the Recklinghausen plant, made on 9 different days between May 27, 1908, and October 10, 1910. Two of these were made in 1908 and the remainder in 1910. The essential figures are as follows: TABLE V ANALYSES OF SPADABLE EMSCHER TANK SLUDGE. RECKLINGHAUSEN Max. Min. Average Water content, per cent 73 6 53 5 65 2 Dry matter, per cent Mineral component of dry matter, per cent Organic component of dry matter, per cent Nitrogen component of dry matter, per cent Fat component of dry matter, per cent Drainage period, number of days 46.5 65.4 58.8 2.39 10.39 22 26.4 41.2 29.8 0.95 3.02 4 34.8 58.5 41.5 1.65 5.28 12.5 It should be noted that the high average water content (65.2 per cent.) of the spadable sludge at Recklinghausen, together 186 SEWAGE SLUDGE with the long average drainage period (12.5 days), is attributable to the overworking of the plant and the consequent lack of thorough decomposition of the sludge. The examination of the dry matter of the drained sludge is made in the same manner as in the case of the liquid sludge. The amount of organic matter is generally somewhat less than that in the liquid sludge, but it may be remarked that in view of the large quantities of material examined, it is very difficult to obtain concordant samples. Experiments on a small scale, however, have shown that some organic matter disappears by gasification during the process of draining. A description of these latter experiments is given in Spillner's earlier paper, pages 161-164. Some instances of such loss in drying are also found in Table X of Spillner's paper relating to the sludge of the Essen-N. W. plant. This table likewise shows that the reduction in the amount of dry matter contained in the liquid sludge, caused by drainage on the sludge beds, ranges from 0.15 to 0.95 per cent. After the spadable sludge has been removed to the final dumping grounds, the process of decomposition continues, although slowly. No analyses have yet been made in regard to this matter, but from the high temperatures (up to 122 F.) that have occasionally been observed in such deposits, it must be con- cluded that further processes of decomposition are taking place therein. EXAMINATION OF THE LIQUID DRAWN FROM THE SEPTIC CHAMBER OF AN EMSCHER TANK, AND THE DRAINAGE WATER FROM THE SLUDGE BEDS A knowledge of the composition of the liquid in the septic chamber of an Emscher tank is of interest to those who operate such plants, because this liquid is contained in the sludge that is discharged from the tank, and is separated therefrom in part when the sludge reaches the drainage beds, and thence finds its way into the outfall. When a tank is first put in service, the septic chamber is filled with the sewage; but as there is no current in this chamber, the original volume of sewage soon becomes septic and undergoes thorough decomposition, after which it has little odor. A renewal of the liquid by diffusion from the sewage that flows through the upper chamber of the tank, or by the water that is mixed with the sludge which drops SEWAGE CLARIFICATION PLANTS 187 into the septic chamber through the slot in the bottom of the upper chamber, is usually a very slow process; but when some of the accumulated sludge is discharged, its volume is necessarily replaced with fresh sewage from the upper chamber. The quantity of sludge discharged at one time, however, is always a very small fraction of the capacity of the septic chamber, and the liquid therein is then allowed to remain at rest for several weeks as a rule. During this time the fresh sewage that' replaced the volume of previously discharged sludge is afforded ample time to become thoroughly decomposed. This process of decomposition is also accelerated by the constant rise of gas bubbles from the sludge below, whereby the liquid contents of the septic chamber becomes thoroughly intermixed. If a sample of the liquid in the septic chamber is taken mid- way between the floating scum at the top of the ventilating openings and the surface of the dense sludge at the bottom, it will be found to be black in color; and on being allowed to stand, the upper portion will gradually become clear while the lower portion will contain much sludge. In the tank a part of this sludge was being carried up by the ascending gas bubbles, and another part was in the act of settling again to the bottom. The averages of the results of a large number of analyses of such liquid is given in the following Table No. VI: TABLE VI ANALYSES OF LIQUID FROM SLUDGE CHAMBER OF EMSCHER TANKS Name of plant Reckling- hausen Boehum Essen- N. W. Number of analyses made 17 6 15 Transparency of the liquid 0.80 1.97 0.34 Reaction of the liquid Alkal. Alkal. Alkal. Chlorine, parts per million 183.0 993.3 2193.9 Residue after evaporation, parts per million 990.7 2594.1 4662.2 Residue after ignition, parts per million 693.7 2379 . 8 3961 . 9 Loss by ignition, parts per million 297.0 214.3 700.3 Suspended matters, parts per million 2171.9 81.8 5670.2 Suspended organic matter, parts per million 1044.3 18.7 3969 . 9 Suspended mineral matter, parts per million 1125.6 63.1 1700.3 Nitrates, parts per million Nitrites, parts per million Total nitrogen, parts per million 36.3 25.4 70.4 Nitrogen as ammonia (NHs), parts per million 27.8 20.5 61.4 Nitrogen rh^-(Q,(N rc a "8 II ^ T ! g * Iff "' gj -c ! g -c 'c3 ^ s ^ si 2 *O a> T3 ' <^ ^ C -X.| ^ 'o ! ti : 'a oj 3 SLUDGE TREATMENT IN THE UNITED STATES 197 TABLE II SUSPENDED MATTER IN THE SEWAGE OF SEVERAL AMERICAN CITIES a. Parts per Million Place Total Organic Mineral Authority Boston, Mass 135 91 44 Kinnicutt, Winslow & Pratt. Chicago, 111 143 80 63 Eng. News, Mar. 31, 1910. Columbus, O 215 81 134 Geo. A. Johnson. Lawrence, Mass 149 113 36 Kinnicutt, Winslow & Pratt. Mass Small towns 94.6 78.1 16.5 Kinnicutt, Winslow & Pratt. Small cities 180.6 46.4 31.2 Kinnicutt, Winslow & Pratt. Paterson, N. J 45 to 641 George C. Whipple. Philadelphia, Pa 204 142 62 Geo. S. Webster. Plainfield, N. J 134 Andrew Gavet. Providence, R. I 397 343.5 53.5 Kinnicutt, Winslow & Pratt. Waterbury, Conn 165 115 50 Eng. News, June 3, 1909. Worcester, Mass 255 . 8 177.8 78.0 Kinnicutt, Winslow & Pratt. b. Gra ms per C apita. Chicago, 111 166 93 73 Eng. News, Mar 31, 1910. Columbus, O 98 47 51 Geo. A. Johnson. Mass. Small cities 53 44 9 Kinnicutt, Winslow & Pratt. Mass. Separate systems. . 49 38 11 Geo. A. Johnson. Mass. Combined and mfg . 145 76 69 Geo. A. Johnson. United States 93 40 53 Geo. W. Fuller. Although the composition of sewage varies greatly in different cities the following analyses may be taken as fairly representing ordinary American conditions. 198 SEWAGE SLUDGE TABLE III COMPOSITION OF TYPICAL AMERICAN SEWAGE In Grams per Capita Daily 1 1. According to George C. Whipple 2 Domestic sewage Sewage of manufacturing cities Total solids Organic matter Mineral matter ... 170 70 100 220 to 500 100 to 200 120 to 300 Chlorine 20 25 to 50 Nitrogen Albuminoid ammonia. . . . Free ammonia Fats 11 1.7 7 20 13 to 15 2 to 4 5 to 10 20 to 50 2. According to George W. Fuller Oxygen consumed .... Nitrogen as . . 2 minutes' boiling . . . . 5 minutes' boiling . . . , Free ammonia . 15.0 . 22.0 7.0 Albuminoid ammonia Organic Total .. 2.5 . 8.0 15.0 Chlorine . 19.0 Fats , . 19.0 Dissolved matter . . Mineral Organic and volatile . Total . 99.0 .. 37.0 . 136.0 Suspended matter. . . . / Total solids . . Mineral Organic and volatile . Total . . Mineral . 53.0 . . 40.0 . . 93.0 . 152.0 Organic and volatile . Total . . . 77.0 . 229.0 1 To convert to ounces per capita multiply by 0.0327. To convert to grains per capita multiply by 15.432. If the volume of sewage is taken as 100 gallons per capita daily: To convert to grains per gallon multiply by 0.1543. To convert to parts per million multiply by 2.6417. 2 Report on Sewage Disposal, Paterson, N. J., 1906. 3 Technology Quaterly, June, 1903, p. 141. SLUDGE TREATMENT IN THE UNITED STATES 199 3. According to E. B. Phelps l In solution In suspension Total Mineral and ash Organic and volatile Total residue on evaporation . . 114 76 190 38 76 114 152 152 304 The organic matter is composed as follows: Total carbon 76 . Total nitrogen 5.7 Total H, O, S, P, etc 70.3 152.0 Separating the nitrogenous from the carbonaceous matter there results: Nitrogenous matter: Nitrogen 5.7 Carbon 28 . 5 H, O, S, P, etc 22.8 57.0 Fats, etc.: Carbon 13.3 H and O 5.7 19.0 Carbohydrates : Carbon 34.2 H, O, etc 41.8 7(>.0 Total.. . 152.0 II. DETRITUS FORM GRIT CHAMBERS Boston, Mass. At the sewage experiment station of the Massachusetts Institute of Technology, the sewage was pumped by a small duplex pump from a large sewer carrying the combined sewage of 350,000 persons. A small grit chamber was formed of 1 Deduced from Water Supply and Irrigation Paper, No. 185. Table, p. 15, Assuming 100 Gals. Per Cap. 200 SEWAGE SLUDGE a cast iron cylinder 19 in. in diameter and 16 in. deep, containing a screen with 1/2-in. meshes. The velocity was reduced in this to 0.04 ft. per second, thus making the time of passage through the chamber about 45 seconds. The detritus removed from this chamber amounted to 0.65 cu. yds. per million gallons of sewage. It contained 27 per cent, moisture and but 6.65 per cent, organic matter, and were quite inoffensive when spread on the land adjoining the station. 1 Analyses of samples taken from March 26 ; 1904, to June 1, 1905, averaged as follows: 2 Clean Fine dry detritus Wet detritus etc. Total Loss on ignition Organic N Oxygen consumed Pounds per mil- 1600 430 190 970 106 2.2 1.7 lion gallons sew- age. Parts per million 190 52 23 117 13 .26 .2 parts of sewage. Near the Moon Island outlet of the Boston Main Drainage system the outfall sewer is enlarged to form two conduits 8 ft. wide, 16 ft. high and about 1/4 mile in length, in which the heavier solids deposit. The depth of sewage in these sewers of deposit is designed to be from 8 to 10 ft. The sludge is pushed toward one end where it is drawn off by a 12-in. pipe to a sludge tank 50 ft.XlO ft.Xl5 ft. in size, having a capacity of 150 cu. yds. From this tank it is taken by a scow, w r hich is towed about 20 miles to sea, and dumped. In the year ending February 1, 1910, with an average flow of 82,378,000 gallons per day, 8773 cu. yds. of sludge was deposited in these sewers, or 0.29 cu. yds. per million gallons of sewage, in addition to whatever was subsequently deposited in the storage tanks on Moon Island. Worcester, Mass. The sewage, which, in 1910, averaged 14.57 million gallons per day, or 107.2 gallons per capita, passed through one of two grit chambers 40 ft. X 10 ft. in plan and 9 ft. deep in about 1.8 minutes. The mean velocity was, therefore, 0.4 ft. per second. 1 Experiments on the Purification of Boston Sewage, Winslow and Phelps. W T ater Supply and Irrigation Paper No. 185. 2 Kinnicutt, Winslow and Pratt. SLUDGE TREATMENT IN THE UNITED STATES 201 According to Mr. Matthew Gault, superintendent of sewers, >.") cu. yds. of heavy grit, about half water and weighing 18,15)7 Ibs. per cubic yard, were removed, representing 4.0 per cent, of the total suspended matter in the sewage. The effluent contained 276 parts per million of suspended matter. The material re- moved amounted to 0.11 cu. yds. per million gallons of sewage. The cost of removal from the grit chambers and placing it in carts (shoveling 3 times) was 33 1/3 cts. per cubic yard, and the cost of hauling about 600 ft. and dumping, 50 cts. per cubic yard, making the total cost of disposal 83 1/3 cts. per cubic yard or 91/4 cts. per million gallons of sewage. Columbus, Ohio. The first grit chamber used at the experi- mental station was 40 ft.XS ft.XT 1/2 ft. deep. This was subsequently changed to 39.5 ft. X5 ft.X2.5 ft. in depth, with a bottom baffle a foot high, 2 ft. from the inlet and a surface baffle extending to about 6 in. from the bottom, 3 ft. from the inlet. In the former the average velocity was 0.518 ft. per minute (2.61 mm. per second) and the period of flow 1.3 hours; in the latter the average velocity was 2.28 ft. per minute (11.39 mm. per second) and' the period of flow 0.29 hour. The results obtained in the two chambers were as follows: TABLE IV Original grit Remodelled grit chamber chamber Per cent, suspended matter in Total 34 22 applied sewage which was i Volatile .... 30 18 removed in grit chamber i Mineral .... 35 24 Cubic yards wet sludge per million gallons 2.55 1.76 Per cent, moisture in sludge, average 87 83 Per cent, volatile matter in dry solids 52 46 COMPOSITION OF GRIT CHAMBER SLUDGE Weight, per cubic yard 1825 Ibs.. Specific gravity 1 .081. Water 82 .4 per cent. Soilds 17.6 per cent. Volatile matter 7.9 per cent. Nitrogen . 22 per cent. Fats 1 .22 per cent It is difficult to reach a comparison of the above results of rapid sedimentation in grit chambers. The quantity and quality of the material removed depends upon various conditions, such 202 SEWAGE SLUDGE as the admission of storm water, the character of street surfaces, the use and efficiency of catch basins for the interception of grit, the velocity, depth and time of passage through the grit chamber and the per cent, of moisture in the detritus. With strictly separate systems and domestic sewage the amount would be so small as to be an insignificant factor in questions of disposal, while in combined systems, where the volume may approximate a cubic yard per million gallons of sewage, the amount of putres- cible matter is usually so small that the detritus may often be used for filling in land. Mr. Emil Kuichling 1 mentions the results obtained in various foreign cities, at the Boston experiment station of the Massa- chusetts Institute of Technology and at the Dorchester pumping station in that city [0.31 cu. yds. per million gallons] and obtains an average of 0.4 cu. yds. per million gallons with a specific gravity varying from 1.52 to 1.87 and a water content of 27 per cent. Under these assumptions the dried suspended matter removed by grit chambers is about 835 Ibs. per million gallons, or 100 parts by weight per million. Waterbury, Conn. 2 The water supply at Waterbury is 139 gallons per capita, and the sewers are on the combined system. The grit chamber was cleaned frequently so that no gases were formed in the detritus. DATA Cu. yds. removed per million gallons of sewage ... 1 .40 Tons removed per million gallons of sewage ..... 1 . 12 Specific gravity 1 . 05 Moisture : 88 . 3 per cent. Solids 11.7 per cent. Mineral matter 5.9 per cent. Fats 0.78 per cent. Nitrogen . 22 : per cent. III. SCREENINGS A sharp distinction should be made between coarse bar screens intended primarily to intercept sticks of wood, orange and lemon peels, rags, etc., and the fine screens having clear openings of 3/8 in. or less, which have been introduced in increasing numbers, 1 Notes on Sewage Disposal, Rochester, 1910. 2 Eng. News, Vol. LXI, p. 596. SLUDGE TREATMENT IN THE UNITED STATES 203 especially in Germany, to remove as much of the matter in sus- pension, including fecal matter, as practicable. The former type is customary in all systems where the sewage has to be pumped, but it has not usually been considered worth FIG. 37. Bar screen, Dorchester Pumping Station, Boston. (Courtesy of F. L. Sanborn, Executive Engineer, Boston Main Drainage.) while to measure the detritus removed. The following figures are, however, available. Boston, Dorchester Pumping Station. Here the combined sewage, amounting in 1909 to 96,373,000 gallons per day, passes through screen cages 7 ft. X3 ft.X7 ft. high, having 3/4 in. 204 SEWAGE SLUDGE vertical bars on 3 sides spaced 1 in. apart and a floor upon which the screenings fall on raising the cage, and from which they are removed by hand and pressed to remove the excess moisture. In the year ending February 1, 1910, 573 1/4 tons of wet filth were removed, or 38.1 Ibs. per million gallons. The cost of labor at the screens was 0.313 cts. per million gallons. Boston Metropolitan System. The screens^ at the several pumping stations of the Metropolitan Sewerage System are in type similar to those at the Dorchester Pumping Station of the Main Drainage works. The screens are composed of 3/4-in. round bars, 1 1/2 in. center to center and a similar series stag- gered in front of these, providing an effective, clear space of about 1/8 in. 1 The following table gives the amount of wet screenings removed from the North and South Metropolitan Systems from the be- ginning of operation, amounting to 0.10 and 0.16 cu. yds. per million gallons, respectively, during the year 1910, or 5 and 10 cu. yds. annually per thousand population. The sewage is partly separate and partly combined in each system. The material removed from the screens at the Charlestown and East Boston Pumping Stations June 10, 1898, had the following composition: 2 Paper 55 per cent. Rags 25 per cent. Hair 5 per cent. Fecal matter and grease 5 per cent. Refuse from slaughter houses 4 per cent. Conglomerate matter 6 per cent. 100 per cent. Columbus Experimental Plant. Two vertical removable screens were used, consisting of a diamond mesh of No. 12 wire, the first having 1/2-in. and the second 3/8-in. openings. These removed 36 of the 215 parts per million of suspended matter con- tained in the sewage, or 0.17 cu. yds. weighing 300 Ibs. per million gallons. The weight per cubic yard was therefore about 1765 Ibs. This amount would undoubtedly have been considerably greater, but for the fact that the sewage treated was not drawn from the invert of the trunk sewer and so did not contain all the grit and coarse heavy matter moving along the bottom. 1 W. M. Brown, chief engineer. 2 Metropolitan Sewage Com'rs, 1899, p. 25. SLUDGE TREATMENT IN THE UNITED STATES 205 & w I ?; ^ i s S 8 I * I S, 206 SEWAGE SLUDGE The liquid, moreover, had previously passed through a 1/2-in. screen and was then pumped, by which much coarse material was removed and fecal matter broken up. Philadelphia Experimental Plant. This was supplied with separate system sewage from a 4 ft. 7 in. intercepting sewer through an 8-in. pipe, which entered the sewer 15 in. above the invert. The sewage was then pumped through 413 ft. of 4-in pipe to a point near the testing station, from which it was drawn by gravity. Some of the heavy solids were probably excluded at the start, and the soft fecal matter must have been disin- tegrated by pumping, as at Columbus. The sewage was delivered through 24 1/4-in. nozzles upon the conical surface of a screen having 32 meshes per inch (clear openings 0.5 mm. square). The amount of suspended matter varied considerably, owing to the admission of trade wastes, but averaged from September, 1909, to April, 1910, inclusive, about 200 parts per million, 7/10 of which was volatile. Of this, 63 parts per million, or 33.5 per cent., were removed by the fine screen, equivalent to 560 Ibs. of dry solids per million gallons of sewage. The effect of screening on subsequent treatment was found to be: 1. A more uniform sewage by eliminating in part the irregu- larities due to trade wastes. 2. A reduction in the sludge subsequently treated. 3. An increase of moisture in the sludge subsequently treated. 4. A finer subsequent sludge and one more readily pumped. 5. An entire absence during 9 months of clogging in sprinkler nozzles using settled screened sewage. Reading, Pa. The only important example as yet of fine screening on a working scale in the United States is that at Reading, Pa., with an apparatus devised by Mr. O. M. Weand. This consists of a horizontal cylindrical framework 6 ft. in diam. X12 ft. long, which is supported on rollers and is rotated by means of a circumferential gear at a rate of 8 revolutions per minute. The cylindrical framework is covered with wire cloth of monel metal having from 30 to 36 meshes to the linear inch, which is, in turn, supported by a screen of No. 12 copper wire with 5 /8-in. meshes. The sewage enters at one end and is distributed by flowing over a weir placed in the first half of the cylinder parallel to the axis. SLUDGE TREATMENT IN THE UNITED STATES 207 It then flows through the bottom of the screen and is conveyed away, leaving the sludge and other coarse material inside. By the rotation of the screen the sludge is worked forward by a narrow spiral plate, which projects from the inner surface until it reaches the further end, where it is lifted by a series of short radial buckets attached to the perimeter. On reaching a certain elevation the sludge slips off upon a sloping trough, which delivers it through the end of the cylinder and drops it into a receptacle from which it is raised and transported by suitable conveying machinery to an elevated sludge tank. The sludge that collects on the screen is washed off by 12 1/16- in. water jets in each of two horizontal pipes placed just outside 208 SEWAGE SLUDGE the screen one on each side. Each pipe is moved back and forth longitudinally by a toggle joint at one end so that the entire surface of the screen can be freed of detritus. Screened sewage has been used in place of water for this purpose satis- factorily, but the jets clog rapidly with the unscreened liquid. Hair, lint and other fibers are not so readily removed, however, and this difficulty, inherent in any fine wire mesh, would prob- ably cause trouble in its use with some classes of sewage. According to Mr. C. B. Ulrich, City Engineer of Reading, the volume of sewage handled is about 5 million gallons daily from 40,000 persons. It contains 125 or 130 parts per million of suspended solids. The screenings amount to 1.15 cu. yds. per million gallons, and have the following general composition: Wet After Centrifuging Moisture 89 . 5 per cent. 73. per cent. Mineral matter 2.8 per cent. 7.4 per cent. Volatile matter 7 . 7 per cent. 19. 6 per cent. lOO.Opercent. 100.0 per cent. The weight of the wet screenings is stated by Mr. Weand, who had, until recently, the contract for operation, to be about 63 Ibs. per cubic foot and the cost of operation, including about 5 h. p. of steam power required for rotating the screen and driving a centrifugal separator, to be $1.00 per million gallons when taking 4 million gallons per day. One difficulty, due to the fine mesh employed, is the frequent stoppage for repairs. This amounted to 1500 hours, equivalent to 63 days, in 1910, and an equivalent of 77 days in 1909. Screens of this type should always, therefore, be in duplicate. Another objection in some cases would be the loss of several feet head caused by the drop in the sewage through the screen. 1 A high percentage of moisture in the screenings is probably inevitable with fine meshes and domestic sewage. In his annual report for 1910 Mr. Ulrich says: "The criterion for screening efficiency should be the thoroughness with which the larger suspended matters are removed and not only mere bulk of re- moved matters. All materials large enough to clog sprinkler- nozzles should be screened out, but it is more economical and just as satisfactory to remove finer solids by sedimentation." 1 By a recently devised modification of design Mr. Weand hopes to save the greater part of this lost head. SLUDGE TREATMENT IN THE UNITED STATES 209 It would appear, too, that with the constant agitation of the fecal matter by the wash water and the rotation of the screen, much of it will have become so finely broken up as to pass through with the sewage. But in spite of these disqualifications, the local authorities are satisfied, on the whole, with the results secured and have recom- mended the installation of a second unit. Screens of this general type are, or soon will be, installed at Atlanta, Ga., Brockton, Mass., New Brunswick, N. J. and Bal- timore, Md. Providence, R. I. Here the screen bars are of wood 1 in. X 10 in. in section, spaced 3/4 in. apart, forming an inclined rack 69 ft. in length, inclined 17 to the vertical, through which the sewage about 19.8 million gallons per day flows, with a depth of from 2 to 5 1/2 ft., averaging about 3 ft. The screen is cleaned continuously by hand with rakes. The screenings, consisting chiefly of paper and rags, amounted, in 1910, to 208 Ibs. or 28.6 Ibs. of dry material, per million gallons of sewage. The wet screenings are placed in perforated cans about 18 in. in diam. X 20 in. in height, which weigh 30 Ibs. each and hold about 230 Ibs. of screenings, in which the material is removed. Waterbury, Conn. With a 1/2-in. mesh of galvanized wire, 140 Ibs. or 0.08 cu. yd. of screenings were removed per million gallons of sewage. 1 The average composition of the screenings for the year ending November, 1906, was as follows: TABLE VI COMPOSITION OF SCREENINGS Parts per million Total Dissolved Suspended Oxygen consumed Organic nitrogen 46 14.8 Total 165 26 84 15.7 26 10.3 Fixed 115 20 4.5 Volatile 50 Suspended matter Fats Particles in micro-suspension Colloidal matter 1 W. G. Taylor, Eng. Rec., June 3, 1909. 14 210 SEWAGE SLUDGE Plainfield, N. J. The. volume of sewage is about 90 gallons per capita. 1 With screens having openings about 1/2 in. apart in the clear, 0.18 to 0.22 cu. yds. of screenings containing 85 per cent, of moisture are removed per million gallons of sewage. Pawtucket, R. I. The strong domestic sewage, amounting to an average of 0.277 million gallons per day in 1910, passes through one of a pair of rack screens 7.96 ft. wide X 4.4 ft. high composed of wooden strips 3/4 in. X3 in. in size, spaced 5/8 in. apart. The depth of sewage passing the screen is about 2.1 ft. During 1910, 1036 cu. yds. of wet material were removed and buried in pits, amounting to 10.25 cu. yds. per million gallons. This large amount is accounted for in part by the fact that it includes a small amount of grit, which is pumpted out once a week from the depressed pit in front of the screen, together with the screen- ings, by an Edson diaphragm pump. Another reason lies in the strength of the sewage and to the fact that it enters the screen chamber 3 ft. below the surface of the liquid. The screenings consist of rags, paper, grease, fecal matter^and kitchen wastes. During the interval between cleaning a mat of grease and other wastes frequently forms in the screen chamber, sometimes to the thickness of 18 in. or 2 ft., of sufficient strength to support a man, below which the material is much more dilute. 2 TABLE VII MATERIAL REMOVED BY SCREENS Cu. yds. wet screenings Lbs. dry solids per Per cent, of suspended solids in wet sludge. (By volume) per million gal. sewage. million gal. sewage Total Volatile Fixed Nov. 10, 1905-Feb. 23, 1906 . . 7.53 746 5.68 4.45 1.23 Mar. 2, 1906-May 11, 1906. . . 5.83 549 5.44 4.36 1.08 Oct. 12, 1906-May 3, 1907 . . . 8.96 792 5.22 4.15 1.07 Feb. 3, 1911-Mar. 24, 1911 ... 10.25 1024 5.89 5.45 0.44 | IV. SLUDGE FROM PLAIN SEDIMENTATION Massachusetts State Board of Health. 3 Experiments were made with Lawrence (combined system) sewage during the years *Eng. News., Vol. LXIII, p. 541. 2 George A. Carpenter, city engineer 3 Rep. 1908, p. 454, et seq. SLUDGE TREATMENT IN THE UNITED STATES 211 1892 to 1897, inclusive, by allowing it to settle while quiescent for 4 hours. Nearly 60 per cent, of the suspended matter and 33 per cent, of the total organic matter, as indicated by the al- buminoid ammonia, were removed. In 1906 a large tank was used for this purpose. The period of sedimentation varied from 2 to 14 hours, and in 2 1/2 years of operation there were removed about 44 per cent, of the suspended matter, as indicated by the albuminoid ammonia in suspension, "58 per cent, as shown by total solids, and 52 per cent, as shown by loss on ignition." 1 Experiments have also been conducted since 1903 with the sewage of Andover, which passed at an average rate of 150,000 gallons per day through a tank holding 13,500 gallons, the average period of sedimentation being about 2 hours. "The average removal of suspended matter by this tank was about 56 per cent, as shown by determinations of albuminoid ammonia in suspension, 71 per cent, as shown by total solids, and 70 per cent, as shown by loss on ignition." About 31 per cent, of the total organic matter was removed. TABLE VIII AVERAGE SOLIDS IN EFFLUENTS FROM TANKS. PARTS PER MILLION Total Loss on ignition Fixed Experiment Sta., 1906-1908: Unfiltered 624 213 411 Filtered 549 156 393 In suspension 75 57 18 Andover., 1905-1908: Unfiltered . . . 446 206 240 Filtered 388 158 230 In suspension 58 48 10 Between July and November 15, 1905, measurements of the sludge were made, giving 1.25 tons per million gallons of sewage. Between April 23 and November 15, 1906, when the daily flow varied from 75,000 to 350,000 gallons, about 2.28 tons of wet sludge were removed per million gallons of sewage, assuming 1 Rep. 1908, p. 454, et seq. 212 SEWAGE SLUDGE the average flow to have been 175,000 gallons per day. This sludge lost 61 per cent, in weight by drying. Analyses of the dried sludge resulted as follows: Organic matter 60 per cent. Carbon 33 per cent. Organic nitrogen 1.6 per cent. Fat 24 per cent. Worcester Experiments. In 1903 a tank having a capacity of 344,000 gallons received an average of one million gallons of sewage per day, which was therefore subjected to 8 hours 7 sedimentation. The suspended matter removed, as indicated by the albumin- oid ammonia, averaged 40.80 per cent., and the total organic matter removed averaged 27.48 per cent. The resulting volume of sludge was 0.125 per cent, of the sewage, or about 6.17 cu. yds. per million gallons, and the water contained was 96.5 per cent. The cost of pressing this sludge into cakes was "$1.56 per million gallons of raw sewage, including handling of pressed cake by trolley to the sludge dump. The other costs of sedimentation, labor and attendance, are given as $1.85 per million gallons/' 1 The composition of this sewage was, in parts per million: Free ammonia 17 . 69 Albuminoid ammonia, Total 8.32 Dissolved 2.88 Suspended 5 . 44 Oxygen consumed, Unfiltered 93.90 Filtered 53 .60 Chlorine 90.40 Columbus Experiments. 2 The two tanks used here were 8 ft. deep and 40 ft. long, and their effective capacity was about 17,000 gallons. The time of retention in these tanks was 8 hours in Tank A and 6 hours in Tank B, giving respective velocities of 4.9 and 6.7 ft. per hour (.42 and .56 mm. per second). The results were as follows when using raw sewage that had first passed through grit chambers: 1 Geo. W. Fuller, Trans. Am. Soc. C. E., Vol. LIV, Part E, p. 178. 2 Rep. Sewage Purification, 1905. Johnson, pp. 88-91. SLUDGE TREATMENT IN THE UNITED STATES 213 TABLE IX RESULTS OF PLAIN SEDIMENTATION WITH RAW SEWAGE Tank A Tank B Influent Effluent Influent Effluent Parts per million Period of operation Aug., 1904 to June, 1905. Nov., 1904 to April, 1905 Oxygen consumed Organic nitrogen 46 8.0 11.7 950 803 147 168 104 64 782 699 83 37 6.4 11.7 875 797 78 137 103 34 738 694 44 47 7.6 . 11.3 927 793 134 164 100 64 763 693 70 39 6.3 11.0 857 784 73 137 99 38 726 685 35 Free ammonia Residue on evaporation: Total Volatile: Total Suspended Fixed: Total Dissolved Suspended . Percentages of removal Oxygen consumed Organic nitrogen 20 10 47 47 53 17 17 6 46 41 50 Residue on evaporation: Total Volatile With raw screened sewage containing about 210 parts per million of suspended matter, or 7 1/2 cu. yds. of sludge 87 per cent, water, the following results were obtained. 1 Rep. on Sew. Purif., Columbus, 1905. Johnson, pp. 151-153. 214 SEWAGE SLUDGE 12345678 Capacity in Hours Flow. FIG. 39. Results of sedimentation, Columbus. Reproduced by permission of the Metropolitan Sewage Commission of N. Y. TABLE X RESULTS OF PLAIN SEDIMENTATION WITH RAW SCREENED SEWAGE Tank A Tank B Period of sedimentation Suspended matter removed: Total Volatile '. Total organic matter removed: Nitrogenous Carbonaceous Fats removed. . Average period of sedimentation Wet sludge per million gallons of sewage 8 hours. 66 % 58% 31 % 31 % 50% 6 hours. 63 % 54% 30% 26% 6 . 8 hours. 5.75 cu. yds. Philadelphia Experiments. Two tanks were first used. Tank No. 12 had a ratio of length to depth of 1.5:1 and a capacity of SLUDGE TREATMENT IN THE UNITED STATES 215 9943 gallons, which was later reduced by sloping the bottom and adding a baffle and scum boards to 8738 gallons. Tank No. 13 had a ratio of length to depth of 2.5:1 and a capacity of 7767 gallons, later reduced as in the case of Tank No. 12, to 5475 gallons. TABLE XI RESULTS OF PLAIN SEDIMENTATION. TANKS 12 AND 13 Conditions Hours storage Suspended solids Parts per million Per cent, removal Average effluent No. 12 No. 13 No. 12 No. 13 No. 12 No. 13 Flat unbaffled 6 4 1/2 3 1/2 6 4 1/2 3 1/2 5.85 55 53 71 60 66 60 81 75 65.5 72.2 64.1 67 59.2 69.3 61 58.7 Flat unbaffled Sloping bottom baffle and scum Sloping bottom baffle and scum Tank No. 17 had a ratio of length to depth of 4. TABLE XII RESULTS OF PLAIN SEDIMENTATION. TANK 17 Suspended solids Conditions Hours storage Parts per million Per cent. * Average effluent removal Unbaffled 10 65 50 4 Unbaffled (stronger sewage) 6 About 65 67 5 Unbaffled . 4 44 81 2 Baffles and scums 4 59 72.5 Baffles and scums 10 46 74 The conclusion drawn from these experiments was that "long storage periods are unnecessary for efficient sedimentation and that great improvement in the uniformity of the tank liquor is obtained by efficient baffling, creating uniform velocity over the entire area of the cross section." A heavy scum formed on Tank No. 13, which received un- screened sewage. After introducing baffles this formed to a thickness of 2 ft., amounting to 5.6 cu. yds., weighing 5 tons. 216 SEWAGE SLUDGE It contained 1810 Ibs. of dry solids and 260 Ibs. of fat, and was very offensive when punctured or removed. The average composition of the sludge was as follows: TABLE XIII COMPOSITION OF SLUDGE Tank No 12 13 17 Sewage Screened Crude Crude Wet sludge: Specific gravity 1 036 1 053 1 043 Per cent, moisture 90 86 1 87 7 Per cent, of dry residue: Volatile . . 49 48 50 Fixed 51 52 50 Nitrogen Fat 1.3 8.1 1.4 7.4 1.3 7.2 The sludge from Tank No. 12, which had been fine-screened, was uniform and with no particle over 1 mm. diameter. It therefore flowed much more freely than that from Nos. 13 and 17, which contained fibers of wool and hops. Scum formed in irregular amounts in these tanks before placing scum boards, but after this was done it formed promptly and increased to a considerable thickness at the inlet end of the tank, being tough and tenacious. The following is a typical analysis of this material when formed on crude sewage: .Average characteristics of scum from Tanks No. 13, No. 17 and No. 19 (Emscher). Specific gravity 1 . 05 per cent. Moisture 82 . 5 per cent, Dry residue 17.5 per cent. The average composition of the dry residue was: Volatile matter 60 . 5 per cent. Fixed 39 . 5 per cent. Nitrogen 1.7 per cent. Fats 13.5 per cent. No scum of this kind formed on Tank No. 12. The fact that the scum floats in spite of its high specific gravity SLUDGE TREATMENT IN THE UNITED STATES 217 is explained by the presence of entrained bubbles of gas which, when liberated on removal, produced an offensive odor. Reading, Pa. Sedimentation here for 15 hours removed 123 of the 165 parts per million of suspended matter. 1 During 1910 a sedimentation tank at Millmont received 1425 million gallons of sewage. Three and three-tenths cubic yards per million gallons were removed with 10 hours' retention and a flow of 3 million gallons per day through a tank 250 ft.X50 ft.Xl6 ft. in size. The composition of the sludge was: 2 Moisture 91 . 83 per cent. Mineral matter 2 .83 per cent. Volatile matter 5 . 34 per cent. The tank was cleaned 6 times during the year, but at no time have there been seriously objectionable odors from the sludge. Kinnicutt, Winslow and Pratt give the following comparison of the results obtained by plain sedimentation at Plain'field, N. J. ; Columbus, O., and Reading, Pa. RESULTS OF PLAIN SEDIMENTATION Period of sedimentation Suspended solids Per cent. Hours Parts per million Influent Effluent Reduction Plainfield, N. J..T Columbus, O Reading, Pa 10.0 13.0 15.0 118 304 165 54 101 42 54 67 75 V. SEPTIC TANK SLUDGE Massachusetts State Board of Health. 3 Experiments with septic tanks have been conducted at Lawrence since 1898 and with Andover sewage from July, 1899, to July, 1902. In five series 4 of experiments the analyses of the sewage and effluent varied between the following limits: 1 Kinnicutt, Winslow and Pratt. 2 Eng. Rec., Vol. LXII, p. 186. 3 Rep. 1908, p. 476, et seq. A sixth series in which sludge was used in place of sewage is omitted. 218 SEWAGE SLUDGE TABLE XIV SUSPENDED MATTER IN SEWAGE AND EFFLUENT Parts pe r million Entering sewage Tank effluent Unfiltered: Total Loss on ignition Filtered: Total 646-912 323-464 475-537 493-571 175-232 448-510 Loss on ignition 174-199 126-173 In Tank A, 70 per cent, of the total suspended matter and 70 per cent, of the suspended organic matter received during 61/4 years were deposited, and of this 82 per cent, of the total and 88 per cent, of the organic suspended matter were destroyed. Again, during a period of 4 1J2 years, 66 per cent, of the total suspended matter and 66 per cent, of the suspended organic matter were deposited, and of this about two-thirds of the total and 80 per cent, of the suspended organic matter were destroyed by digestion; The period of sedimentation averaged in the first case, about 12 hours, and in the second case, 15 hours. In Tank G, in which the period of sedimentation was about 6 hours, 60 per cent, of both the total and organic suspended matter was deposited. In Tank H, with 18 hours' storage, 75 per cent, of the total and 78 per cent, of the suspended organic matter were deposited, while 84 per cent, of the total and 90 per cent, of the organic matter which deposited were destroyed. In Tank F, which received a sewage with about 50 per cent, more suspended matter than Tank A, and more than twice that of Tanks G and H, 76 per cent, of the total and 82 per cent, of the organic suspended matter were deposited, while of this, 71 per cent, of the total and 86 per cent, of the organic matter were destroyed. Tank B received a sewage about 10 times as strong as G and H. Here 82 per cent, of the total and 84 per cent, of the organic suspended matter were deposited, and 74 per cent, of the total and 82 per cent, of the organic suspended matter in this were destroyed. SLUDGE TREATMENT IN THE UNITED STATES 219 TABLE XV C.M POSITION OF DRY SEPTIC TANK Si.i IH.I; Per cent. Number of tanks from which sludge was sampled Mineral matter 45 6 to 70 9 6 Total organic matter Organic nitrogen . . 54 . 4 to 29 . 1 1.1 to 2.9 6 6 Fats ! Carbon Hydrogen 8.8 to 11.9 25.1 to 29. 8 3 . to 4.0 4 3 3 Madison, Wis. Here, by septic tank treatment, 42.8 per cent, of the suspended solids and 60.8 per cent, of the albuminoid ammonia are removed. 1 TABLE XVI SUMMARY OF RESULTS SHOWING ACCUMULATION AND LIQUEFACTION OF SLUDGE Septic tank A B C D E Aug. Aug. Nov. Feb. Mar. 16 16 22 18 9 Period of service 1904-5 to to to to to June June June June June 30 30 30 30 30 Days in service 300 301 221 132 118 Total million gallons of sewage treated 9.5 5.7 10.8 4. 1 0.79 Average period of flow (hours) 13.9 21 .8 8.0 4.0 8.0 Average velocity of flow millimeters per second 0.24 0.15 0.42 0.84 0.14 Tons dry solids per million gallons: In applied sewage 0.61 0.61 0.62 0.86 1.21 Deposited in tank 0.31 0.31 0.28 0.26 0.67 Escaped in effluent 0.30 0.30 0.34 0.66 0.54 Tons dry solids per million gallons: Deposited 2 0.40 0.40 * 0.36 0.33 d.86 In tank at end of tests 0.21 0.29 0.12 0.20 0.43 Per cent, solid matter liquefied 48 28 67 39 . 50 Cubic yards wet sludge per million gallons sludge 1.4 1 K 0.8 1.5 2.9 treated found in tank at end of test. Columbus Experiments. Five septic tanks were used in the* Columbus experiments. Tanks A, B, C and D received the effluent from the grit chamber, and A received the sewage after screening. Tanks A, B and C were 8 ft. X40 ft. in plan with 1 Purification with special ref. to Wis. conditions. Geo. J. Davis, Jr., and J. T. Bowles. Bui. Univ. Wis., Oct., 1909. 2 Corrected in ratio of 28 to 36 to correspond to ratio of computed deposit to actual deposit respectively in plain sedimentation Tank A. 220 SEWAGE SLUDGE an effective capacity of 17,000 gallons. Tank D was circular, 12 1/2 ft. in diameter, with an effective depth of 5 1/2 ft. It was baffled so as to make the length of flow 40 ft. and had an effective capacity of about 5370 gallons, and was covered. Tank E was a cylindrical boiler shell 6 ft. diameter by 15 ft. long, air-tight, with a 1/2-in. gas pipe leading to a rneter. The effec- tive depth was 5 ft. and the capacity 7200 gallons. In general, it may be assumed that in Tanks A, B and C the average accumulated deposit amounted to 1.33 cu. yds. per million gallons as compared with 3.3 cu. yds. per million gallons with plain sedimentation. The percentage liquefied was there- fore about 60. The 50 per cent, liquefied with crude sewage in Tank E was believed to be a fair average to use in estimates. The composition of the resulting septic sludge was found by analysis to be as follows: TABLE XVII COMPOSITION OF SEPTIC TANK SLUDGE Tank A B C D E Weight of wet sludge pounds per cubic yards 1836 1823 1823 1800 1833 1 089 1.080 1.080 1.069 1.087 83.3 82.3 83.2 84.7 83.7 Solids, per cent 16.7 4.4 17.7 4.4 16.8 4.3 15.3 4.1 16.3 5.0 0.25 0.25 0.23 0.19 0.18 Fats 0.94 1.06 1.05 1.36 1.17 The reduction of suspended matter secured at Columbus during the years 1909 and 1910 by septic tank-treatment was as follows: TABLE XVIII REDUCTION OF SUSPENDED MATTER* Maximum Minimum Mean 1909 1910 1909 1910 1909 1910 Daily volume of sewage, million gallons 21 .4 Period of flow through tank, hours 36 17.9 3.1 17.0 4.3 2.5 3.5 11.1 10.1 12.9 7.2 Total suspended matter, parts per million : Screened sewage Septic effluent 1088 230 630 264 13 12 16 9 201 82 211 80 i Furnished by W. W. Jackson, Supt. Water Works. SLUDGE TREATMENT IN THE UNITED STATES 221 Pawtucket, R. I. 1 In 1900, 41.5 per cent, of the organic matter was removed by the tanks. At the end of 10 months' operation the accumulation of sludge was 5.428 cu. yds. per million gallons with 81.75 per cent, moisture. The dried solids amounted, therefore, to 0.99 cu. yds. per million gallons of sewage. 377.33 parts per million, or 1.868 cu. yds. of mineral matter were de- posited in the tank for each million gallons of sewage. The amount of dried solids removed by septic action was, therefore, 1.87-0.99 = 0.88 cu. yds. per million gallons. The cost of its removal was 411/3 cts. per cubic yard. This treatment has now been discontinued. Mansfield, O. 2 The sewage from about 10,000 persons, 40 per cent, of which is collected by the separate system and which is much diluted with ground water, flows at a rate of about one million gallons per day through bar screens with 3/4-in. openings, and is then settled in 4 septic tanks 92 ft. 3 in. X52 ft. in plan, having an effective depth of 7 ft. and a combined capacity of 1 million gallons. The crude influent sewage contains but 34 to 42 parts per million of suspended matter, and the effluent contains 34 parts per million, showing very little reduction. The following is a more recent analysis. Parts per million of suspended matter: Total Volatile Crude sewage 74 55 Septic effluent 85 to 135 43 to 54 The sludge resulting from 4 years' operation weighed 1868 Ibs. per cubic yard. It had a specific gravity of 1.11, and con- tained: Moisture 80 . 8 per cent. Nitrogen 1 . 03 per cent. Volatile matter. 3 . 6 per cent. Fats 4.7 per cent. It was granular in structure and not offensive when removed from the tanks. Exposed in thin layers for about 4 days the black color, due to ferric sulphide, disappeared, leaving the material similar to humus. The cost of disposal for the 1200 cu. yds. of sludge removed was about 50 cts. per cu. yd. Plain fidd, N. J. 3 The population of 20,550 persons furnishes 1 Rep. of City Eng'r for year ending Sept. 30, 1900. 2 Rep. St. Bd. Hlth., 1908. 3 Eng. Rec. Vol. LXIV, p. 29. 222 SEWAGE SLUDGE about 1.9 million gallons per. day of domestic sewage to 4 septic tanks having a combined capacity of 1.35 million gallons. In March, 1910, 1600 cu. yds. of wet sludge and scum were removed, equivalent to 3.35 cu. yds. per million gallons of sewage treated during the previous 11 months. In March, 1911, 1650 cu. yds. of wet sludge and scum were removed, equivalent to 3.01 cu. yds. per million gallons of sewage treated during the previous year. No objectionable odors were given off except while the tanks were being emptied. In 1910 the average suspended matter, in parts per million, was as follows: In screened sewage 152, varying from 114 in February to 271 in November. In septic effluent 56, varying from 42 in May to 72 in December. The percentage of removal was, therefore, 64.5. The fats averaged 42.8 parts per million in the screened sewage, and 27.7 parts per million in the septic effluent, the percentage of removal being about 35. Waterbury, Conn. 1 Observations were made here of the results obtained with two septic tanks 14 ft. X6 ft. 3 in. X6 ft. in size, of a capacity of nearly 4000 gallons each, beginning in June, 1905, and lasting 18 months. The time allowed for sedimentation varied from 8 to 33 hours, and the results were as follows: TABLE XIX REMOVAL OF SOLIDS IN SEPTIC TANKS Tank No. 2 Tank No. 3 Average period of sedimentation. Hours. . . . Horizontal vel in mm per sec 15.5 08 11. 0.11 Wet sludge in tank. Cu. yds. per million gal- lon sewage. Dry solids deposited. Tons per million gal- lon sewage. Per cent retained in tank . ... 1.07 0.25 56 0.55 0.25 36 Eng. News, Vol. LXI, p. 596. SLUDGE TREATMENT IN THE UNITED STATES 223 TABLE XX COMPOSITION OF SEPTIC SLUDGE AND SCUM IN TERMS OF THE WET MATERIAL Sludge Scum Tank No. 2 Tank No. 3 Tank No. 2 Pounds per cubic yard 1721 1.02 86.3 13.7 5.9 0.16 1.53 1738 1.03 85.4 14.6 7. 0.22 1.52 1637 0.97 80.9 19.1 8.9 0.34 2.00 Specific gravity Moisture, per cent Total solids, per cent Volatile, per cent Nitrogen, per -cent Fats, per cent Saratoga, N. Y. 1 The volume of flow amounted in 1904, to from 1 1/4 to 2 1/2 million gallons daily of weak domestic sewage, the population varying from 12,000 in winter to 50,000 in summer. COMPOSITION OF SEWAGE Free ammonia Albuminoid ammonia Oxygen consumed . . . Suspended solids Parts- per million 20 4 50 . 200 There are 4 septic tanks 91 1/2x51. 1/2 ft., holding 8 ft. depth of sewage, or with a total capacity of 1,000,000 gals. The period of retention of sewage was 10 to 15 hours. From July, 1903, until January, 1905, no sludge was removed from septic tanks. The following shows the results of the treatment: Total dry solids received 500 tons. Dry solids passed in effluent 175 tons = 35 per cent.. Dry solids in tank, Jan. 1, 1905 100 tons = 20 per cent. Dry solids removed by digestion 225 tons = 45 per cent. 1 Eng. Rec., Vol. LI, p. 84 and Rep. N. Y. Dept. Hlth., 1907, Vol. II. 224 SEWAGE SLUDGE The composition of the sludge and scum was as follows : Sludge Scum Wet material: Specific gravity 1.025 0.975 Moisture 94 . per cent. 86 . 5 per cent. Dry residue: Volatile 4 . 5 per cent. 10.0 per cent. Fixed 1 5 per cent. 3 . 5 per cent. VI. SLUDGE FROM EMSCHER TANKS Philadelphia Experiments. Experiments were made in Phila- delphia with an Emscher tank 5 ft. in diameter and 10 ft. deep. The conical bottom inclined 30 degrees to the horizontal. By a cylindrical baffle, the motion of the sewage was first downward from the annular influent channel surrounding the central vent and then upward to the effluent at the periphery about 41/2 ft. in each direction. The sludge chamber was about 4 ft. in effective depth. The time of passage was about 2 hours. Dur- ing 3 months' use (Jan. 12 to April 13, 1910) 53 per cent, of the suspended solids were removed, leaving in the effluent 92 parts per million. The sludge produced had the following characteristics: Wet sludge: , Specific gravity 1 085 Moisture 82 . 5 per cent. Volume per million gals, of sewage 0.9 cu. yds. Dry residue: Volatile 38 per cent. Fixed 62 per cent. Nitrogen 1 . 2 per cent. Fats 6 . 5 per cent. The results obtained are not strictly comparable with those from a tank of the 30 ft. depth recommended by Dr. Imhoff. The deeper tank would produce a sludge with less moisture and with a larger amount of entrained gas, which would be of subse- quent value in assisting the process of drying. SLUDGE TREATMENT IN THE UNITED STATES 225 The evolution of gas appears to have been quite active in the sludge chamber. It was inodorous and presumably composed chiefly of methane (CH 4 ). As withdrawn from the tank the sludge was ''fine, granular and homogeneous; considering its relative dryness, it flowed freely and did not have an offensive odor. When withdrawn from the sludge outlet, the odor was decidedly 'tarry/ and after a few days the dried mass was inodorous." The solids appeared to have been completely digested. The composition of the scum was as follows: Wet sludge: Specific gravity 1 . 05 Moisture 87 .2 per cent. Dry residue: Volatile 61.8 per cent. Fixed 32 .8 per cent. Nitrogen 1.9 per cent. Fats 14.3 per cent. Chicago Experiments. 1 Experiments with the Emscher tank have been carried on by the Chicago Sanitary District. The total depth of the circular tank was 17 ft. and the inside diameter 7 ft. 6 1/2 in. An 18-in. central vent pipe was supported by a conical hood separating the two chambers and a cylindrical baffle caused the sewage entering near the central vent to descend to a depth of at least 3 ft. from the surface and then rise to the opening leading to the 2-in. effluent pipe. The sludge chamber had a total depth of 12 ft. 3 in., the lower 4 ft. forming a cone with a slope of 45 degrees. The sewage flow amounted to 48,500 gallons per day from May 26 to June 7, 1910, 31,000 gallons per day from June 8 to Sept. 12, and then 13,500 gallons per day to Nov. 1. It was first passed through a 5/8-in. screen and then pumped from midrdepth at the screen chamber through 400ft. of force main and a grit cham- ber to the tank. The time of passage through the tank was about 2 hours, the latter part of the time the capacity of the upper chamber being 1175 gallons. The reduction of suspended matter was from 64 per cent, to 69 per cent, after the operation was well established. About 2 cu. yds. of sludge were produced 1 George M. Wisner, Chief Engineer, and Langdon Pearse, Assistant Engineer, the Sanitary District of Chicago. 15 226 SEWAGE SLUDGE per million gal. of sewage during the summer and fall of 1910, having the following characteristics, and 0.93 cu. yds. per million gallons of completely digested sludge per million gallons during a period of 5 months. 1 Wet sludge: Specific gravity 1 . 04 Moisture 86 to 90 per cent. Dry residue: Volatile matter 39 per cent. Fixed matter 61 per cent. With prolonged operation, and where the sludge chambers are of sufficient depth, any mixing of the top and bottom layers of sludge will be prevented and there will be a gradual move- ment downward toward the bottom. As the sludge approaches the outlet, the organic ingredients are more and more decomposed so that a more favorable condition, when discharged, may be expected than in the case of the comparatively small experi- mental plants at Philadelphia and Chicago. The following table gives comparative data for several plants in the Emscher district. 2 TABLE XXI RESULTS OF TREATMENT IN THE EMSCHER DISTRICT J-l.CUli.lllJ. tuouoou j\j\j UUJJJ. Sewage Effluent Sewage Effluent Sewage Effluent Suspended solids: Total 466.6 127.5 402.0 93.3 449.8 135.4 Organic 259.3 73.5 186.9 56.4 261.6 85.6 Mineral 207.3 54.0 215.1 36.9 188.2 49.8 Average percent, removal of 72 7 7 7 total suspended solids. Period of sedimentation, hours . 3/4- 1 1/4 1-1 1/2 1/2 -1 Sludge, cubic yards per million 1 65 2 .1 1. 39 gallons. Per cent, moisture in sludge .... 82 .9 3 78 - 1 75 .6 In comparing these results with those obtained at Philadelphia, the German plants are seen to handle a much denser sewage combined with a lower percentage of moisture in the sludge resulting from briefer periods of sedimentation. It should be remembered, too, that the sewage in the Emscher District 1 Rep. on Sew. Disp., Chicago, Geo. M. Wisner, 1911. 2 Technisches Gemeindeblatt., Mar., 1911. Eng. News, Vol. LXV, p. 663. 3 The sludge space at Recklinghausen is insufficient for complete decomposition. SLUDGE TREATMENT IN THE UNITED STATES 227 includes large volumes of trade ^wastes. For these reasons further experience under normal American conditions, and with full-sized plants, are necessary before the true relative value of this process can be established. In a paper presented by Mr. Charles Saville 1 to the Boston Society of Civil Engineers, 2 he states that from 65 to 75 per cent, of the suspended solids in the sewage are usually removed. The scum formed is generally of small amount and quite odorless. It requires loosening with a rake once a month or so, to permit the escape of gas and allow much of it to deposit, but about once a year it becomes necessary to remove the scum from the' surface. The sludge is drawn off at intervals of from 2 weeks to 6 months, preferably the more frequent period. This should not be done by suction as this removes the entrained gases which it is desir- able to retain incorporated with the sludge until placed on the drying bed; nor should withdrawal be so rapid as to permit the formation of a cone at the surface and the consequent entrance of sewage, as described by Eisner. The effluent pipe should then be filled with water or sewage to prevent the formation of an interior crust and consequent clogging with the next dose of sludge. The energy with which digestion takes place probably depends to a great extent on the temperature. In the Emscher District the temperature in the sludge chamber remains practically between 55 and 63 even in winter. If the tanks were above ground or in a much colder climate the sludge chamber would probably have to be of greater capacity on account of the de- creased bacterial activity. In the design of Emscher tanks the space required for sludge storage should be approximately known. Until more is known regarding the rate of progressive concentration, due to digestion, it will be safe to assume the volume of the sludge during storage a mean between that required for fresh sludge and that finally produced by the Emscher tank from the sewage treated during the assumed period of storage. The volume of fresh sludge and the period of retention may be assumed from the data already given in the discussions by Dr. Eisner and Dr. Spillner. If we assume 80 per cent, moisture in Emscher sludge and 90 1 Associated with the firm of Hering and Gregory. Formerly with the Emschergenossen- sctiaft at Essen. 2 Dec. 28, 1910. 228 SEWAGE SLUDGE per cent, in freshly settled sludge, the latter will occupy twice the volume of the former, and an equal mixture will occupy 11/2 times the volume of Emscher sludge when completely digested. Therefore, if: v = ftow of sewage in gallons per capita per day V = total daily flow of sewage p = population served D = days' retention of sludge C = effective capacity of digestion chamber in cubic feet. DV Then, for combined sewage, C = 10,500 = 10,500 PD, and DV for separate sewage, C= 5,250 = 5,250 PD. If we know the parts per million of suspended solids that may be expected to settle out from a known sewage in its passage through the sedimentation chamber and if we accept the esti- mate of Spillner and Blunk (see page 177), as to the reduction in the volume of sludge by its passage through the digestion chamber of the Emscher tank and by subsequent air-drying, there will result the quantities given in the following table. TABLE XXII VOLUME OF SLUDGE AND AIR-DRIED SLUDGE PER MILLION GALLONS OF SEWAGE OF DIFFERENT DENSITIES FROM SEPARATE SYSTEMS RESULT- ING FROM EMSCHER TANK TREATMENT Suspended solids in sewage deposited parts per million Cubic yards fresh sludge Cubic yards Emscher sludge moisture 75 per cent. 1 Cubic yards spadable air-dried sludge 2 Moisture 95 per cent. Moisture 90 per cent. 25 2.48 1.24 0.40 0.16 50 4.95 2.48 0.79 0.32 75 7.43 3.72 1.19 0.48 100 9.90 4.95 1.58 0.63 125 12.38 6.19 1.98 0.79 150 14.85 7.43 2.38 0.95 175 17.33 8.17 2.77 1.11 200 19.80 9.90 3.17 1.27 225 22 28 11.14 3.56 1.42 250 24 . 75 12.38 3.96 1.58 275 27 . 23 13.12 4.35 1.74 300 29 . 70 14.85 4.75 1.90 1 Equals 16 per cent, of sludge with 95 per cent, moisture. 2 Equals 40 per cent, of Emscher sludge. SLUDGE TREATMENT IN THE UNITED STATES 229 Imhoff gives the sludge produced by the combined sewage of Bochum as 0.2 liters, or 0.007 cu. ft. per capita daily. 1 If v = the sewage flow per capita daily, the sludge resulting from each million gallons of combined sewage will be 7000/v cu. ft., or 260/v cu. yds. The sludge resulting from separate sewage, Dr. Imhoff says, is about half as much. With these assumptions, the following table of sludge volumes, which was prepared by Mr. John H. Gregory for the Metropolitan Sewerage Commission, of New York, gives the sludge output that will require final disposal. TABLE XXIII SLUDGE PRODUCED BY THE EMSCHER TANK WITH SEWAGES OF DIFFERENT STRENGTHS Sewage flow gallons per 24 hours Volume of sludge Separate system 0.0035 cu. ft. per capita per day =3. 5 cu. ft. per 1000 pop. per day. Combined system 0.007 cu. ft. per capita per day =7.0 cu. ft. per 1000 pop. per day Per capita Cubic feet per million gallons Cubic yards per million gallons Cubic feet per million gallons Cubic yards per million gallons 50 70 2.6- 140 5.2- 60 . 58 + 2.2- 117- 4.3- 70 50 1.9- 100 3.7 75 47- 1.7 + 93 + 3.5- 80 44 1.6 + 88- 3.2 + 90 39- 1.4 + 78- 2.9- 100 35 1.3- 70 2.6 110 32- 1.2- 64- 2.4- 120 29 + 1.1- 58 + 2.2- 125 28 + 1.0 + 56 2.1- 130 27- 1.0- 54- 2.0 140 25 0.93 50 1.9- 150 23 + 0.86 47- 1.7 + 160 22- 0.81 44- 1.6 + 170 21- 0.76 41- 1.5 + 175 20 0.74 40 1.5- 180 19 + 0.72 39- 1.4 + 190 18 + 0.68 37- 1.4- 200 17+ 0.65 35 1.3 Wasser und Abwasser, Feb. 4, 1911, p. 446. 230 SEWAGE SLUDGE VII. SLUDGE FROM CHEMICAL PRECIPITATION Massachusetts State Board of Health. 1 A large number of experiments have been made by the Massachusetts State Board of Health on chemical precipitation. These indicate that by the proper use of copperas, ferric sulphate or alum, all the suspended matter and from 25 to 43 per cent, of the soluble organic matter of sewage as indicated by albuminoid ammonia may be removed. " Using equal values of the different precipitants, applied under the most favorable conditions for each, upon the same sewage, the best results were obtained with ferric sulphate. Nearly as good results were obtained with copperas and lime, while lime or alum alone gave somewhat inferior effluents." During the 5 years, beginning with 1893, sewage was treated with 1000 Ibs. sulphate alumina per million gallons, and allowed 4 hours for sedimentation. As a result there was removed: Total albuminoid ammonia, 56 per cent., varying from 50 to 63 per cent., in different years. Albuminoid ammonia in suspension, 78 per cent., varying from 72 to 83 per cent, in different years. Fats, 59 per cent., varying from 47 to 80 per cent, in different years. Worcester , Mass. 2 The sewage in 1910 averaged 14.57 million gallons per day (or 107.2 gallons per capita), including 3.47 million gallons of infiltration and a large amount of factory waste, rendering it decidedly acid. Of this volume an average of 9.81 million gallons of sewage per day were treated with 989 Ibs. of lime per million gallons. After from 6 to 12 hours of pre- cipitation, 3 the sludge produced amounted to 22 cu. yds. per million gallons, representing 77.8 per cent, of the suspended organic matter. This is drawn off by a floating arm and raised by Shone ejectors to a storage tank where 30 to 50 Ibs. of lime per thousand gallons is added in the form of milk of lime. 15 or 20 per cent, of the supernatant liquid is drawn off to sand niters and the heavy sludge pumped under a pressure of 80 Ibs. per square inch to filter presses. When pressed, this produces 3.69 tons of 1 Rep. Purification of Sewage and Water, 1890, p. 786. An. Rep., 1908, p. 457. 2 An. Rep. Supt. of Sewers, 1909-10. 3 There are six primary tanks, operated in series, 100 ft. X66 2/3 ft. X 7 ft. in size with a capacity of 350,000 gallons and 10 secondary tanks, operated in parallel, 166 2/3 ft. X40 ft. X7 ft. in size with a capacity of 350,000 gallons. SLUDGE TREATMENT IN THE UNITED STATES 231 sludge cake per million gallons, which is taken by cars 3/4 of a mile and dumped on low-lying ground. It has not been found economical to reduce the moisture by pressing as low as 60 per cent., but rather to let the cakes dry on the dump. 1 The results of precipitation are shown by analysis as follows. RESIDUE ON EVAPORATION Parts pel * million Per cent. A ve. sewage Ave. effluent removed Total: Total 789 697 11.7 Dissolved 545 637 -16.9 Suspended Volatile: 244 60 75.4 Total . . : Dissolved . 367 228 300 271 18.3 18 9 Suspended Fixed: 139 29 79.1 Total 422 397 59.2 Dissolved 317 366 -15.4 Suspended 105 31 70.5 TABLE XXIV RESULTS OF CHEMICAL PRECIPITATION AT WORCESTER, MASSACHUSETTS Ten years, 1901-10 Year ending Nov. 30, 1910 Maximum Minimum Average Moisture in wet sludge, per cent 91 .80 94.75 90.20 92.39 Moisture in sludge cake, per cent 68.4 73.0 67.8 69.4 Tons solids per million gallons sewage 1 . 17 1 . 74 j . 99 1.37 treated. Pounds lime added per 1000 gallons 53.5 53.5 20.0 40.7 sludge. Cost of operation: Per million gallons sewage $4 . 53 $6.33 $3.85 $5.05 Per ton solids $3.88 $4.33 $3.39 $3.74 1 An. Rep. Supt. Sewers, 1898-99. 232 SEWAGE SLUDGE Providence, R. I. The average volume of sewage treated per day for the year 1910 was 14,652,329 gallons. The total sewage produced was about 15 million gallons per day, and the popula- tion served was 199,000, making 75 1/2 gallons of combined sewage per capita. This contains wastes from wool-washing, dyeing, bleaching and jewelry works, and its analysis shows the following albuminoid ammonia in parts per million: Suspended, 4.84; soluble, 4.68. Total, 9.52. This was treated with 485.5 Ibs. of lime per million gallons, removing 48.32 per cent, of the organic matter (as albuminoid FIG. 40. Sludge presses, Providence. (Courtesy of Mr. O. F. Clapp, City Engineer.) ammonia), and 82.64 per cent, of the suspended matter. The sludge amounted to 23.15 cu. yds. per million gallons and con- tained 92.07 per cent, moisture. Sedimentation takes place, first, in 4 primary tanks 11.87 ft. deep and then in 16 secondary tanks 8.67 ft. deep, whose aggre- gate effective capacity is 11.13 million gallons. About 93 per cent, of the sludge is removed by the primary tanks, so that at times it has been possible to omit the use of the secondary series. The sludge is forced under a pressure of about 70 Ibs. per square inch to 18 presses holding from 43 to 54 plates, each 36 in. SLUDG1-: TREATMENT IN THE UNITED STATES 233 square, by which it is pressed into cake from 3/8 to 1 1/4 in. thick. About ">.()! tons of cake per million gallons of sewage are produced, or 0.24 ton per cubic yard of wet sludge. The pressed cake contains 72.4 per cent, moisture. Forty-seven pounds of lime per thousand gallons were added to the sludge before press- ing. Two men working together will remove about 50 tons of cake from the presses in 10 hours. Ordinarily, eight men are employed on 16 presses. The cost of chemical precipitation in 1910 was $3.11 per million gallons of sewage, and that of sludge disposal, $4.06, making the total cost $7.17. The sludge pressing cost $2.62 per ton of solids. Alliance, Ohio. 1 About 1.6 million gallons of sewage per day were received by a separate system of sewers from 6500 persons in 1907 and passed though 2-in. and 1/4-in. bar screens to 3 precipitation tanks, 80 ft. X40 ft. X6 ft. in size, having a total capacity of 420,000 gallons. The sludge is pressed, reducing the moisture from 88 per cent, to 47 per cent., 1500 tons of wet sludge furnishing 60 tons of pressed cake, or 2.5 tons of cake per million gallons of sewage. The sludge cake is usually taken away by farmers for fertilizer. The cost of operation was, in 1906, 45 cts., and in 1907, 55 cts. per capita. Canton, Ohio. 1 About 2 1/2 million gallons of domestic sewage were contributed daily in 1908 by a population of about 23,500. After passing a screen rack 2 ft. 6 in. X 4 ft. 2 in. in size, inclined 20 degrees to the vertical, and composed of 3/1-6 in. Xl 1/4 in." bars, set 7/8 in. apart, the sewage, which contains but 43 parts per million of suspended matter on account of the large proportion of ground water, is treated with about 13.6 grains of lime per gallon (1 ton per million gallons) on week days, and half this amount on Sundays. It then passes to a series of 4 tanks 100 ft. X50 ft. Xo ft. in size, having a total capacity of 700,000 gallons, for precipitation. The surface velocity was measured in the first of these tanks and found to be 41 ft. per minute. In the other three tanks it was 27.8 ft. per minute. The period of retention was 6.7 hours. The first two tanks are cleaned 3 times a week, the last two 2 times a week. The sludge is pumped to neighboring fields and plowed under, but this mode of disposal has not proved satisfactory. 1 Rep. State Board of Health, 1908. 234 SEWAGE SLUDGE The cost of operation in 1901 was $3850, which, at 2 1/2 million gallons per day, would be $4.22 per million gallons. In winter, with plain sedimentation, 13.7 cu. yds. of wet sludge were removed in this way per million gallons of sewage, while in warm weather, with chemical precipitation, the amount removed was 14.3 cu. yds. per million gallons. The suspended solids, which amounted to about 86 parts per million, were reduced by about one-half in each case, and with chemical precipitation the total organic matter was reduced by about the same amount. The greater part of the sedimentation took place in the first tank. The results of several analyses are given in the following table: TABLE XXVI REMOVAL OF SUSPENDED MATTEK AT CANTON Parts per million Per cent. Tons of removed dry solids removed Total Volatile per million Total Volatile gallons Sewage Effluent Sewage Effluent sewage Plain sedimentation: Jan 16 1907 83 41 42 29 51 31 0.175 Feb 26 1907 124 61 62 28 51 55 0.263 Chemical precipitation : Aug. 9, 10, 1906 43 42 31 30 2 3 0.004 July 17, 1907 89 51 47 40 45 17 0.158 July 18, 1907 118 58 65 30 51 54 0.250 1 | Although about 50 per cent, of the organic matter is removed, the effluent is unstable and not entirely satisfactory, and the extra cost, due to the use of chemicals, does not appear to be justified by the results. The annual cost of operating the works is about 15 cts. per capita of population. White Plains, N. Y. 1 This plant, operated under the patent process of J. J. Powers, will soon be discontinued owing to the construction of the Bronx Valley trunk sewer. In 1907 there were nearly 14,000 persons contributing about 850,000 gallons of strictly domestic sewage daily. 1 Rep. N. Y. State Bd. of Hlth., 1907. SLUDGE TREATMENT IN THE UNITED STATES 235 This passed through a vertical screen of 1/8 in. X 1/2 in. bars 4 ft. long spaced 1 in. center to center, to a sedimentation cham- ber 45 ft. X 24 ft. in size; 5 or 6 barrels (1200 to 1300 Ibs.) of lime were added daily with a varying amount of perchloride of iron frequently a carboy (140 Ibs.) a day. When removing sludge, once a week, the tank is disinfected with chlorine, as described hereafter for the East New York plant. The sludge, amounting to about 35 cu. yds. per week, or 5.9 cu. yds. per million gallons of sewage, is pumped to 2 drying beds having an area of about 3600 sq. ft. After drying, a small part of this is utilized as a fertilizer. The annual cost of the process for material was: Coal, 145 tons at $5 . 25 Perchloride of iron, 300 carboys of 140 Ibs. at $0.0275. Lime, 2,240 bbls. at 1 .40 Vitriol, 40 carboys of 140 Ibs. at $0.0275 $ 761.25 1,155.00 3,136.00 154.00 $5,206.25 or $16.78 per million gallons treated. Brooklyn, N. Y. 1 The Borough of Brooklyn, New York, maintains 4 chemical precipitation plants, employing the process patented by J. J. Powers. Two of these are at Coney Island, one near Sheepshead Bay, and the third and largest at East New York. Being similar in principle, the latter, only, will be described. The sewage, amounting in 1907 to about 12 million gallons per day from a population of about 100,000 persons, including the surface drainage from 3200 acres, is first dosed with lime to the amount of 5 bbls. per million gallons and then enters, in parallel, two sedimentation channels 16 ft. wide X 7 ft. deep X 350 ft. long. From these it passes to a well 40 ft. in diameter from which it is pumped to an outfall flume. For from 36 to 48 hours before cleaning out the tanks the sludge is disinfected with chlorine generated from 108 Ibs. sulphuric acid, 64 Ibs. common salt and 48 Ibs. manganese dioxide. The sludge is then pumped on to shallow lagoons excavated near the plant and dried. 1 Rep. Metropolitan Sewerage Com. of N. Y., 1910, p. 259. 236 SEWAGE SLUDGE TABLE XXVII RESULTS OF ANALYSES OF SEWAGE MADE DEC. 11, 1907, AT EAST NEW YORK DISPOSAL PLANT BY DR. D. D. JACKSON. PARTS PER MILLION Raw Effluent Dissolved Suspended Total Dissolved Suspended Total Total solids 441 136 577 454 134 588 Loss on ignition 1 176 115 291 110 98 208 Fixed solids j 265 21 ! 286 344 36 380 Fats and fatty acids 397 234 At the four above-mentioned plants there were said to be produced in 1907 33 1/3 cu. yds. of sludge per million gallons of sewage. There were used for precipitation 1.15 bbls., or 263 Ibs. of lime and 133 Ibs. of perchloride of iron per million gallons of sewage, and for disinfection of sludge there were used: Lbs. per million gal- lons sewage Lbs. per cubic yard sludge Sulphuric acid 2 8 084 Salt Oxide of manganese 1.6 1 2 .048 036 Regarding the efficacy of these plants, Dr. D. D. Jackson states : "The process of purification has not materially reduced either the suspended matters or matters in solution. ***** The effluent is * * putrescible at the end of 24 hours." VIII. THE DISPOSAL AND UTILIZATION OF SLUDGE 1. Disposal of Night Soil on Farms The most primitive as well as a most effective method of utilizing sludge is by its direct application to the land as a SLUDGE TREATMENT IN THE UNITED STATES 237 fertilizer. By the removal of fecal matter from cesspools before it has been diluted with any large volume of water, the processes of sedimentation and separation are avoided, although for other reasons the use of cesspools is not to be advocated. This method of disposal has been employed up to the present time on such a large scale in Baltimore, Md., that a brief description is given here. A contract is entered into with the city by which the right is secured to charge the householder a certain sum for the removal of night soil. This is drawn by suction with "odorless excava- tors" from the cesspool when it becomes necessary, and con- veyed to barges holding 450 loads of six barrels (about 200 gallons net) each, for which the contractor operating the barges receives 25 cts. per load for disposal. In 1909, according to Dr. James Bosley, Commissioner of Health, 61,748 loads were removed in this way, in addition to which more or less finds its way, illegally, by other channels to farming land in neighboring counties. 1 The barges are towed down the Patapsco River, chiefly to Bear Creek, about 8 miles distant, where their con- tents are pumped by specially designed pumps of large capacity to lagoons prepared for its reception by the farmers. An ordinary lagoon or pit holds a scow load, or about 100,000 gallons, and the operation of pumping occupies about two hours. For this amount, which is delivered to him as required, the farmer paid the contractor several years ago $1.67 per thousand gallons. The heavy sludge remaining in the scow is removed by shoveling into carts and is also taken by the farmer. The pits are used merely for storage until the material is required, when it is bailed with long-handled dippers into tank carts and sprinkled over the fields. A large variety of crops is fertilized in this way. One farmer stated that he had used 6 barge loads of night soil (at the rate of 4000 gallons per acre) and 35 barge loads of garbage (also handled in this way) during the year on 150 acres of kale, cab- bage, tomatoes, potatoes and spinach. The liquid portion appeared to be more immediately effective, but the heavier portion produced a more lasting effect. The odors in the vicinity of these lagoons are very offensive, biit, so far as known, they have not had an unfavorable effect on the health of those living on the farms. The nuisance from 1 Also, about 2030 houses are connected (1911) with storm water drains. Dr. J. M. Bosley. 238 SEWAGE SLUDGE flies has been considerable and the possibility of conveying disease by them should not be forgotten. A more serious objection lies in the illegal use of night soil on growing vegetables before gathering for the market. This is very difficult to prevent on account of the inaccessible location of the farms. Application to the crops is supposed to be made several weeks (10 in the case of kale) before gathering. With the introduction of sewers this system of disposal and utilization will, of course, be abandoned. 2. Dumping at Sea Disposal of sludge by dumping at sea, as practised at London, Glasgow, Dublin, Manchester and Salford, is almost unknown in the United States. The cost at several of these places is as follows: TABLE XXVIII COST OF TRANSPORTING SLUDGE TO SEA. ADAPTED FROM REPORT V, ROYAL COMMISSION ON SEWAGE DISPOSAL Total cost in Pont a Place Years Average tons of sludge per annum 1 Average per cent, moisture in sludge cents of sea disposal incl. int. and sinking fund per ton of sludge 1 Cents per ton of dry solid matter 1 uents per ton of sludge 90 per cent. water 1 Remarks Glasgow 1906-7 341,600 86.8 9.7 74.0 ! 7.42 60 year loan. Salford ! 1902-6 152,320 79.0 17.1 81.5 ; 8.15 Heavy canal dues. Dublin 1906-7 128,307 90. 9.0 90.9 9.09 No harbor dues, short distance. London 1903-6 2,838,080 92.0 8.2 103.0 10.30 Manchester .... 1903- 188,720 86. 17.4 124.7 12.47 Heavy canal 4-5-7 dues. Southampton . . 1 906-7 15,624 90. 30.5 305 . 9 30.59 By contract. Further details are given in the following table : : 1 Tons referred to are of 2000 pounds. 2 Fifth Rep. Royal Com. on Sew. Disp., p. 167. SLUDGE TREATMENT IN THE UNITED STATES 239 TABLE XXIX Works For year Per cent, moisture Cost per ton Cost per million gallon Land charges Sea charges Total Land charges Sea charges Total London: 1907 1907 1907-8 1906-7 92.04 91.65 86.69 $0.050 0.046 0.016 0.044 $0.067 0.067 0.049 0.117 $0.117 0.113 0.065 0.161 $1.57 0.78 0.34 $2.10 1.13 1.06 $3.67 2.91 1.40 (llasgow: Dalmuir Manchester The first three sludges are from chemical precipitation and the last from septic tank treatment. Recently Providence has disposed of its sludge cake by dump- ing it in Narragansett Bay from a scow 135 ft. long X 38 ft. wide Xll ft. deep. This is divided into 6 compartments and has a capacity of 850 cu. yds. when filled level, and 1050 cu. yds. when heaped. This is towed about 10 miles down the bay and deposited in a depth of about 65 ft. of water. As already mentioned, the sludge removed from the deposit sewer of the Boston Main Drainage is taken by a scow out into Massachusetts Bay and dumped in deep water. Disposal of sludge by dilution is also practised at Columbus, Ohio, where it is stored until the river water is in freshet or of sufficient volume to render its discharge unobjectionable. This was also tried with the sludge from the experimental tanks at Waterbury, Conn., where it was observed that when diluted by 1650 volumes of water in the Naugatuck River, there were no apparent odors resulting and the mixture was non-putrescible. 3. Application to the Land Direct application to the land is frequently employed at small works. The ordinary cost of this is given by Mr. W. B. Ruggles as from 40 to 50 cts. per ton of the solid content and the area required is from 1 to 2 acres (2 or 3 in. deep) per 1000 tons of sludge. 1 Where trenching and burying is used, the cost is about 9 to 1 4 cts. per ton of wet sludge, or from 90 cts. to $1.40 per ton i Kinnicutt, Winslow and Pratt. 240 SEWAGE SLUDGE of solids, exclusive of the cost of land. The area required is from 1/4 to 1/2 acre per 1000 inhabitants/ or from 0.2 to 0.4 acres per 1000 tons of sludge. At Mansfield, Ohio, the total cost of disposing of 1200 cu. yds. of septic sludge on the land, employing 6 men and a horse at a cost of $15 per day, was about 50 cts. per cubic yard. About 40 cu. yds. were handled per day of 8 hours. No nuisance is experienced except during the operation of emptying the tanks, when there is a noticeable odor. At White Plains, N. Y., the sludge from chemical precipitation is pumped once a week on to land to a depth of 3 in. In about 7 days it dries sufficiently to be winrowed and is later wheeled to a dump. About 5 cu. yds. were produced from a population of 14,000. Two sludge beds of 1800 sq. ft. each were used alter- nately. Drying in lagoons is practised in Reading, Pa., the area required being about 1/4 acre for the 4280 cu. yds. of wet sludge produced in 1910. No offensive conditions were noted during the year. Experiments were conducted at the Philadelphia testing sta- tion with drying in 4 lagoons 8 ft. X 12 ft. in size. With sludge derived from plain sedimentation, the results were, as follows: TABLE XXX RESULTS OF DRYING SLUDGE IN LAGOONS. PHILADELPHIA | Time in days I Depth in inches Per cent, moisture Rainfall, inches Cubic yards sludge per acre Screened. . . 12.20 82.8 1600 Screened. . . 26 7.67 57.0 1000 Screened. . . 49 3.50 51.6 0.43 470 Screened. . . 13.50 90.1 1800 Screened. . . 62 7.00 61.0 3.14 950 Crude . .1 12.00 88.7 1600 Crude 59 4.70 62.8 2.59 640 In general, wet sludge 12 in. deep dries to about 60 per cent, moisture in 6 weeks, leaving about 0.4 of the original volume to be removed from the bed or lagoon. 1 Eng. Rec., Vol. LXIII, p. 79. SLUDGE TREATMENT IN THE UNITED STATES 241 Sludge from the Emscher tank dried rapidly and soon became odorless. It was run onto a bed under cover consisting of: Fine sand . . Gravel .... *"" I Foundation resembling nat- Gravel 6m. > .... rtj . ural conditions. Broken concrete This was underdrained by 3-in. perforated tiles. It was found that 12 in. of sludge placed on this bed in winter was in condition to be removed in 12 days, although containing 68 per cent, moisture. The average time for drying in the Emscher District, according to Mr. Charles Saville, 1 is about 7 days, but in summer it is sometimes removed after but 2 days, the moisture in the dried sludge varying from 55 to 65 per cent. Experiments were made in lining the lagoons with various materials: coarse sand, fine sand, rice coal and sawdust. Coal and sawdust were favorable to subsequent incineration while sand was liable to form clinker. "The thick layer of sawdust was more efficient than the thin, whereas the thick layer of coal was less efficient than the thin, and the thick layer of sawdust was equally efficient to the thin layer of coal." About the same amount of moisture was removed by sand and sawdust, this being about 75 per cent. At the Elmhurst (Borough of Queens, New York) plant the supernatant water is drawn from the tank at mid-depth. The sludge with the remaining roily liquid is then placed on a sludge filter 20 ft. X 50 ft. in area and 3 ft. 3 in. deep. The filter is under cover. It is made of graded material varying in size from 3 in. at the bottom to sand, with 4 in. of combustible material usually buckwheat coal at the top. The bed is un- derlain by a system of 2 1/2-inch steam pipes to facilitate drying. The heavy liquid is delivered to the surface of the bed by a 12-in. pipe and a trough. The filtrate passes by underdrains to a pump well and the de-watered sludge is scraped, with the coal, from the surface after about 3 days' drying, and burned under boilers. 2 Tests made at the Chicago experimental plant showed that sludge from plain sedimentation containing 90 per cent, moisture 1 Ass't Eng'r Emscher Association, Eng. News, Vol. LXV, p. 664. *Eng. Rec., Vol. LII, p. 87. 16 242 SEW AGE SLUDGE dried out to a thickness of 4 in. with but 50 per cent, moisture in 30 days during warm weather. At Brockton, Mass./ the dried sludge raked from the inter- mittent filters was first burned on wood fires. As this caused a nuisance, it was then (1890) sold to farmers for $125, and later (1901 to 1906) for $150 per annum. Since 1909 it has been given away so as to secure a prompt removal. In 1908 the sludge averaged 136,000 gallons per day and contained 11,177.5 parts per million of total solids. It produced about 3500 tons of dry sludge. The rakings were of the following composition: Moisture 16 . 22 per cent. Phosphoric acid 78 per cent. Potassium oxide 51 per cent. Nitrogen 1 . 45 per cent. Calcium oxide ' .30 per cent. Insoluble matter, sand, etc 70. 13 per cent. This is used as a fertilizer on corn, potatoes, millet and other grasses, but, with the exception of corn, additional potash and phosphoric acid are required. In general, the cost of raking and removing the sludge from intermittent sand filters in Massachusetts amounts to about $3 per million gallons of the sewage applied, or from 12 to 30 cts. per capita of population. In the arid portion of the west, conditions are more often favorable to the direct application of the raw sewage to the land. According to Dr. W. F. Snow, Secretary of the State Board of Health of California, some towns in that state operating sewage farms realize from $500 to $5000 a year in the crops of hay, walnuts, potatoes, alfalfa and eucalyptus wood produced. According to Dr. Voelcker, 2 the yield of corn (wheat, etc.) is increased from 10 to 12 per cent, by the application of sewage sludge to the extent of 40 Ibs. of nitrogen to the acre, while artificial fertilizers of equivalent strength increase the yield from 16 to 17 per cent. The use of sludge increases, in particular, the stem of the plant and therefore the straw produced, but in any case its value depends even more on the amount of moisture and the lime contained than upon the percentage of nitrogen. He concludes that from a practical point of view none of the sewage 1 Eng. News, Vol. LXII, p. 251. 2 Fifth Rep. Royal Com. on Sew. Disp., p. 187. SLUDGE TREATMENT IN THE UNITED STATES 243 sludges used would be worth 10s. ($2.50) a ton on the farm for wheat-growing purposes. The economical use of sludge as a fertilizer being exceptional, its disposal on land is reduced to either merely drying or burying. As to the choice of these, Mr. George W. Fuller states: 1 1. That sludge drying beds are usually unsatisfactory for large plants and that when they have been used with a moderate degree of success this has usually been during cool weather. 2. That the burial of sludge in trenches has merit in the case of small installations, but that in the case of large plants this cannot compete with the employment of the Emscher tank, the product from which is inoffensive and is therefore easily dis- posed of. 4. Filter-pressing Pressing sludge is usually confined to plants employing chem- ical precipitation and where, therefore, there are large volumes of a rather watery product to be handled. At Worcester this process cost, in the year ending November 30, 1910: Per million gallons of sewage, $2.76 Per thousand gallons of sludge, $1.20 Per ton of solids, $3.50 The cake is used for filling in land. At Providence the total cost of sludge disposal in 1909 was $4.22 and in 1910 $4.06 per million gallons of sewage, and the cost of sludge pressing was $2.85 and $2.62, respectively, per ton of dry solids. Aside from the Worcester and Providence plants, where the cost data are carefully kept, the information to be had from American practice is so meager that the following supplementary figures referring to sludge pressing in England are given. In Leeds, according to W. W. Ruggles, 2 the cost of pressing was, in 1910, but $14,784.61 for 16,0.17 tons of dry solids, or about 92 cts. per ton. 1 Sewage Disposal with respect to Offensive Odors. M. I T. Congress of Technology, April, 1911. 2 Exclusive of sewage beds and niters. Sewage Sludge Disposal, Eng. Rec., Vol. LXIII, p. 79. 244 SEWAGE SLUDGE Mr. Ruggles gives the cost of cremating sludge cake as about $3 per ton of dry material, and that of carting and dumping the cake as seldom less than 60 cts. per ton and frequently two or three times that amount, depending on the haul. According to the Royal Commission on Sewage Disposal, 1 the cost of pressing sludge under ordinary conditions, reducing the moisture, 90 to 95 per cent, in the raw sludge, to about 55 per cent, in the pressed cake, may be taken as follows: TABLE XXXI COST OF PRESSING SLUDGE INCLUDING INTEREST AND SINKING FUND Wet sludge per ton Pressed cake per ton For populations of 30,000 or more and j 13.2 cts. to 15.6 cts. 59.7 cts. to 70.6 cts. ordinary sewage. For populations less than 30,000 and where, on account of septic or greasy sludge, 5 to 20 per cent, lime had to be added. 18.1 cts. to 28.0 cts. 81.4 cts. to $1.249 According to Santo Crimp, if the moisture is reduced by press- ing to 50 per cent., the product from each inhabitant will equal 2 cwt., or 0.112 ton, per annum after efficient chemical precipi- tation. Pressed sludge cake weighs, according to Rideal, 82/3 tons per million gallons of sewage, and the moisture can be reduced from 50 per cent, to 12 per cent, by air drying. The value of this air-dried sludge he estimates for different English plants as follows: From $2.48 (Birmingham using lime, and Windsor employ- ing the Hilles process) to $5.90 (Coventry using sulphate of alumina) per ton of 2000 Ibs. The dried sludge at Aylesbury, where the ABC process is employed, is valued at $7.10 per ton. 5. Drying with Centrifugal Machines Drying by centrifugal machines has hardly been attempted in the United States. While admitting the excellent results ob- tained by the Schaefer-ter Meer machine abroad, its high first cost has prevented its introduction into this country up to the present time. 1 Fifth Rep. Royal Com. on Sew. Disp., p. 170. SLUDGE TREATMENT IN THE UNITED STATES 245 A centrifugal dryer of more simple construction is used al Reading, Pa., however, for de-watering the material received from the rotary screen. The sludge is delivered with 89.5 per cent, moisture by a screw conveyer to canvas bags. These are placed by hand in the hydro-extractor, which is about 6 ft. in diameter and 31/2 ft. high. On removal the moisture has been reduced from 89.5 to 73 per cent., 19.6 per cent, of the product being volatile, and the weight has been reduced from 62-70 to 31-351bs. per cubic foot. The material taken from the machine is burned under the boilers of the sewage pumping station. The manual labor required in the operation is a serious objec- tion to this type of dryer in connection with large plants. FIG. 41. Centrifugal sludge-drying machine at Frankfort, Germany. (Courtesy of The Lathbury-d'Olier Co., Philadelphia.) In Bradford, England, the cake from sludge presses is heated in a rotary drier, which reduces the moisture from 33 to about 9 per cent., leaving the dried product in a form suitable for shipping. This is said to find a ready market at $2.17 per ton and has proved so profitable that similar machines are to be installed at the sewage treatment plant at Dublin. The cost of producing the dried product for use as a filler for 246 SEWAGE SLUDGE fertilizers under American conditions is estimated by Mr. Ruggles as follows: Cost per ton Filter pressing $1 . 00 Drying .35 Grinding 16 Bagging 15 Total $1 . 66 While its value as a fertilizer, which has been separately estimated at $6.76 and $10.79 per ton, is assumed to be at least $4, leaving a profit of $2.34 per ton. 1 The cost per cu. yd. of dried sludge at Hanover has been estimated at 36 cents and in America would probably be more than double this amount. 2 Kinnicutt, Winslow and Pratt give the probable cost of dry- ing by centrifugal machines as from 5 to 7 cents per cu. yd. of wet sludge. With regard to the Schaefer-ter Meer machines, the following data are from the operation of the 4 units installed at Hanover: Dried material produced per unit per day 26-39 cu. yds. Dried material produced per million gallons sewage 3 . 3-4 . 9 cu. yds. Cost of operation: Per unit per day $12 . 85 Per capita per annum .02 Per million gallons sewage 1 . 62 Per cubic yard wet sludge . 07-. 10 Per cubic yard dried sludge . 33- . 50 6. Recovery of Calorific Value No attempt has been made to utilize the latent calorific value of sludge on a large scale in the United States, but some experi- ments have been made in this direction by the Massachusetts 1 Estimate made by a " well-known laboratory in New York." Ammonia, 2.6 per cent $6.52 Equivalent of bone phosphate, .66 per cent .07 Potash, .24 per cent .' .17 $6.76 Estimate on sample furnished The American Fertilizer of Philadelphia. Nitrogen, 52 .2 Ibs. at 20 cts $10 .44 Phosphoric acid, 2.2 Ibs. at 4 cts 09 Potash, 6.2 Ibs. at 4 .25 cts .26 $10.79 2 Rep. Sew. Disp. Chicago. Geo. M. Wisner, 1911. SLUDGE TREATMENT IN THE UNITED STATES 247 State Board of Health, 1 by the city of Worcester, Mass., 2 and by the City of Philadelphia. 3 In 1898 the Massachusetts State Board of Health demon- strated that gas was evolved from the sludge rather than from the soluble contents of sewage. In the year 1900 the following volumes of gas were produced in a septic tank, illustrating clearly the effect of temperature. TABLE XXXII GAS PRODUCED IN SEPTIC TANK April 21 May 2 to July 10 to Oct. 4 to to May 1 May 22 July 20 Oct. 6 Average hours storage 28 21 28 23 51 52 74 65 Cubic feet gas per 1,000,000 gallons of 6100 8400 11300 6000 sewage passed. Cubic feet gas per 1000 gallons of tank 5.3 9.5 9.5 5.3 capacity. Cubic feet gas per cubic foot sludge in tank 0.71 1.27 1.27 0.71 To illustrate the effect of varying composition, the amount of gas obtained from the fermentation of different sludges was determined. TABLE XXXIII AMOUNT OF GAS PRODUCED BY FERMENTATION OP DIFFERENT SLUDGES Per cent. Centimeters of gas formed per Source Days organic matter in gram of sludge Sludge Organic matter Tannery sewage 61 51 0.00 0.00 Lawrence sewage 26 84 0.34 0.40 Lawrence sewage Septic tank . . 21 30 78 46 5.80 7.45 4.14 9.00 Septic tank gas was found to be composed principally of methane, carbon dioxide and nitrogen. The methane varied from 28.7 to 79.0 per cent. When obtained from the fermenta- 1 Rep. Mass. St. Bd. Hlth., 1908, p. 492, et seq. 2 Eng. News, 1892. 3 Rep. Bureau of Surveys, comprising work at the sewage experiment station at Spring Garden, Philadelphia, 1910, p. 191, et seq. 248 SEWAGE SLUDGE tion of sludge, the methane varied from 79 per cent, in the case of septic sludge to 2 per cent, in the case of ordinary sewage sludge. TABLE XXXIV V COMPOSITION OF GAS PRODUCED Per cent. Source C0 2 CH 4 N Septic tank A 3.4 79.0 16.0 Septic tank B 42.2 37.5 19.0 Andover septic tank 9 8 28 7 61 Sludge from, regular sewage .... 28.7 1.8 69.5 Sludge from septic tank 11.7 75.9 12.4 Experiments were begun in 1908 on the distillation of gas from sludges of different kinds. The average volumes produced were as follows: TABLE XXXV GAS PRODUCED PER TON OF DRY SLUDGE From settled sewage sludge 6600 cu. ft. From chemically precipitated sewage sludge, j 8100 cu. ft. From septic sludge j 4900 cu. ft. From peat | 8400 cu. ft. From soft coal ! 8600 cu. ft. to 12,900 cu. ft. While the composition of the gases depended much on the source of the material, those from sludge contained, in general, more CO 2 and CO and of "the so-called illuminants" than those derived from coal, while the H and CH 4 were less in quantity. The resulting coke amounted to from 45 to 65 per cent, of the weight of the dry sludge and, although containing much mineral matter, could no doubt be burned as fuel. Analyses of this showed from 1.1 to 1.7 per cent, of available P 2 O 5 and about 22 per cent, of the nitrogen in the sludge. "Much of the fats * * * * distilled over with the* tars. * * * This by- product could readily be disposed of by mixing it with the coke SLVDdK TREATMENT IN THE UNITED STATES 249 and burning, or if it were formed in sufficient amounts it could be burned directly, in the same manner as water gas tars are utilized." TABLE XXXVI ANALYSES OF SLUDGES USED, PER CENT. OF COKE FORMED AND AMOUNT OF NITROGEN IN COKE Source Composition of sam- ple before distillation per cent. Per cent, coke produced Per cent. N (by wt. of total sludge) Per available P 2 5 in coke Total N Loss on ignition Fats Found in coke As NH 3 in washer Lawrence (settled sewage) . Andover (settled sewage) . . Clinton (settled sewage).. . Brockton (settled sewage) Worcester (chem. precip.) Septic tank 3.36 2.14 2.36 1.76 1.19 2.46 2.54 36.8 46.6 74.4 46.6 44.5 47.9 92.0 96.8 12.8 27.5 7.7 6.2 3.2 8.3 63.5 59.5 44.5 60.5 54.0 68.5 49.0 77.3 .11 .67 .72 .94 .09 .27 .70 .586 .226 .404 .137 .544 .497 .700 222 1.33 1.33 1.44 1.17 1.67 1.15 0.31 Peat Soft coal (aver, of 4 kinds steam and gas coal). TABLE XXXVII GASES PRODUCED BY DESTRUCTIVE DISTILLATION OF SEWAGE SLUDGE Source Cu. ft. gas per ton of sample C0 2 Illumi- nants o CO H CH 4 N Lawrence (settled sewage) 4900 4.4 2.2 0.3 30.7 34.9 18.6 9.1 Andover (settled sewage) ' 6400 7 4 15.1 6 14.3 22.9 34.3 5 4 Clinton (settled sewage) 9100 8.3 6.7 ?0 4 33 9 24.5 7 Brockton (settled sewage) 6000 16.5 21.4 0.2 10.3 22.6 29.1. 0.2 Worcester (chem precip ) 8100 14 2 "* 4 9 ? 29 8 32 6 16 2 2 2 Septic tank 4QOO 7 5 1 1 24 '3 44 13 10 2 Peat . . .... 84nn 39 4 7 2 11 O 28 17 1 Soft coal 10200 I i 1.6 2.0 0.1 5.2 62.3 25.7 3.2 Illuminating gas (Lawerence) 3.4 9.1 0.021.542.5 19.7 3.8 The Worcester experiments referred to were made in 1891 and consisted in burning 45 tons of sludge containing 46 per cent, moisture with the aid of 3 cords of wood. The total cost of its disposal, including the manual labor of collecting the sludge from the beds and conveying it to the furnace, was $3 per ton of dry sludge. 250 SEWAGE SLUDGE At the Philadelphia sewage experiment station wet sludge was mixed with an equal weight of rice-size anthracite coal. The resulting mixture was 1.57 times the volume of the sludge and its specific gravity 1.29. The percentage of moisture was reduced in this way from 91 per cent, to 48 1/2 per cent. After placing in a sludge lagoon to a depth of 12 in. and drying 24 hours, this was reduced to about 27 1/2 per cent., and in 9 days to 22 1/2 per cent., the temperature being about 37 F. The result of the mixing is shown in the followng table: Constituents Per cent. Lbs. per cu. yd. Moisture ... . . 45.5 50 4.5 1,069 1,175 106 Coal Dry residue of the sludge 100. 2,350 Each cubic yard of wet sludge, after drying, with 1760 Ibs. of coal, produced one ton of the dried mixture delivered at the boiler house for fuel. The British thermal units contained in the materials used were: In the coal as received 12065 In the sludge as burned 1216 to 2165 TABLE XXXVIII RESULTS OF BURNING AIR-DRIED SLUDGE WITH COAL Weight of sludge broken to 2-in. size, per cu. yd. in Ibs, Percentage of water in sludge Percentage of dry residue, volatile Lbs. dry residue in sludge used Lbs. volatile matter in sludge used Lbs. coal burned with sludge Lbs. wet sludge burned per minute Lbs. volatile matter burned per minute Lbs. dry residue burned per minute Lbs. of coal burned per pound of Wet sludge Dry residue Volatile matter 710 to 1015 15.3- to 40.2 24.5 to 30 168 48 192 2.66 . 555 to 2.18 to 233 70 285 4 .68 to .817 to . 233 to 15 .705 2.47 .895 .945 .25 SLUDGE TRKA TMENT IN THE UNITED STATES 251 The experiment demonstrated that it was possible to burn sludge in this way under boilers, but the degree of economy effected was not determined. Samples were then taken of air-dried screened sewage sludge, crude sewage sludge and Emscher tank sludge and mixed with equal weights of pea coal, and of wet sludge mixed with equal weights of rice coal, but the moisture to be evaporated inter- fered with realizing their full caloric value. The small coal con- sumption it was believed, however, would frequently justify the employment of this process in connection with sludge disposal. TABLE XXXIX RESULTS OF TESTS OF FUEL VALUE FOR STEAM PRODUCTION OF MIXTURE OF SLUDGE AND COAL Per cent, wet sludge in mixture Fuel prior to burning Lbs. water evap. per Ib. fuel Eqivalent evaporation from and at 212 F . per Ib. of fuel Moisture b.t.u. Rice coal and wet 12.4- 2.75-3.87 10700-11252 4.20-4.50 4 , 60-4 . 92 sludge. 22.9 Pea coal and dry | 50 1.1 5-2 . 03 8832-8875 2.67-3.32 2.92-3.63 sludge. CHAPTER IX SUMMARY AND CONCLUSIONS In selecting the best method for removing the solid matter suspended in sewage we must consider the kind of subsequent treatment, if any, it is to receive. If the effluent is to be put through sprinkling niters or contact beds or if it is to be applied to the land it should be delivered in as fresh a condition as possible and the coarser particles should be removed by screens, scum boards, grit chambers or a combination of some such de- vices. Otherwise the process will be more offensive and the filter beds more likely to clog. If it is to be discharged into a stream, too coarse material should be removed as causing de- posits on the bottom or an offensive appearance of the surface of the water. If, however, it is to be utilized on account of its calorific or fertilizing properties the sludge from plain sedi- mentation or Dortmund tanks or that from fine screens is pref- erable to the more completely mineralized product from septic or Emscher tanks. If septic tanks are employed the grit need not ordinarily be first intercepted, .but may be handled in connection with the other sludge, but in the case of Emscher or Dortmund tanks the grit is undesirable, as tending to clog the discharge pipe. Chemical precipitation is sometimes to be preferred in the case of a very strong sewage or one containing acid wastes in large quantity, or in case it is thought best to press the sludge into cake. If the sludge is to be buried, air dried, used for filling in land or dumped at sea the septic and Emscher tanks have the advantage of furnishing a product of small volume which may be readily handled with the minimum offense. Fine screening requires but little room and therefore should be considered where land values are high, but in this case, as well as in plain sedi- mentation, the resulting detritus or sludge contains so large an amount of moist organic matter that its prolonged storage is objectionable in populous districts. These questions have been so fully treated by Dr. Eisner in Part I that it is unnecessary to dwell further on them here. 252 SUMMARY AND CONCLUSION 253 Having decided on the general method to be employed the results that may be expected, based on experience in the United States, are about as follows: TABLE XL REMOVAL OF SUSPENDED SOLIDS BY DIFFERENT METHODS OF TREATMENT Method Per cent. Cu. yds. sludge Per cent. removed per mil. gal. sew. moisture Bar screens, spaces 3/4 in. to 1 in 2 to 10 0.1 toO.25 65 to 75 Mesh screens, spaces 1/4 in. or less 15 to 25 0.6 to 1.4 80 to 90 Grit chambers 5 to 10 0.1 toO.8 35 to 50 Plain sedimentation 50 to 70 4 to7 87 to 93 Septic tanks 50 to 70 1.5 to3 80 to 90 Emscher tanks 50 to 70 1 to 2 75 to 85 Chemical precipitation 75 to 90 20 to 25 86 to 92 These figures are subject to so great a variation, depending on local conditions, that they are merely given as a guide to indicate the limiting values under ordinary conditions. Cubic Yards of Wet Sludge containing 100 Ibs.of Dry Residue. .0123456 Sp.Gr.1.06 FIG. 42. Volumes of sludge with varying percentages of moisture. (Reproduced from Report on Disposal of Sewage, Philadelphia, 1911.) The sludge produced has generally been given heretofore in cubic yards. In England it is more customary to mention the product by weight and as this is also frequently done in the United States the following equivalents may be found useful, although these are subject to variation, depending on the char- acter of the ingredients and the space occupied by air after draining. 254 SEWAGE SLUDGE TABLE XLI APPROXIMATE WEIGHT OF A CUBIC YARD OF SLUDGE Per cent, moisture Pounds Tons 100 1685 0.84 95 1695 to 1705 0.85 90 1720 to 1775 0.86 to 0.88 85 1750 to 1820 0.87 to 0.91 80 1790 to 1865 0.89 to 0.93 In selecting the method of treatment the cost is an important, and sometimes the controlling, factor. The septic tanks at Washington, Pa., cost $4173 per million gallons treated daily or $15,650 per million gallons gross capacity, 1 while the corre- sponding costs for the larger Columbus, O., tanks (the contract price for which was particularly favorable) were $3340 and $8320, respectively. Rectangular Emscher tanks with 3 hours' retention of sewage and 5 months' retention of sludge would probably cost from $5000 to $7000 per million gallons daily flow or from $30,000 to $40,000 per million gallons gross capacity, depending on the excavation. The following figures on a per capita basis are given by Mr. George M. Wisner, Chief Engineer of the Chicago Sanitary District. 2 TABLE XLII COMPARATIVE COST OF SETTLING TANKS BASED ON A SEWAGE FLOW OF 200 GALLONS PER CAPITA DAILY Type City Nominal period of settling Cost per capita for construction Straight-flow Columbus O 6 hours $0.58 Straight-flow Columbus O 8 hours $0.77 Dortmund tank Emscher tank . . Gloversville N. Y Atlanta Ga . . 4 hours 3 3 hours 3 $0.84 $1.44 In case the area available for sludge drying is limited or costly the Emscher tank has a decided advantage, as fully explained 1 According to Mr. D. M. Belcher, Assoc. M. Am. Soc. C. E. 2 Eng. Rec., Nov 4, 1911. 3 Sludge storage not considered. SUMMARY AND CONCLUSION 255 by Spillner and Blunk. As a result of the Chicago Experiments Mr. Pearse is of the opinion that with G to 8 hours' retention of sewage in a septic tank the sludge requires at least 20 days to become spadable, whereas with but from 1 to 3 hours' retention of sewage in an Emscher tank the sludge is in condition to be handled in about 5 days, requiring, therefore, not more than one-fourth the area. For plain settled sludge a still larger area is required amounting to from 1 to 2 acres per 1000 tons if air dried, or from 0.2 to 0.4 acres per 1000 tons if buried. See page 239. It is concluded that the land required for Emscher tanks amounts to 0.63 sq. ft. per capita or, with appurtenances, W sq. ft. per capita; and that for the drying beds there should be provided 0.3 sq. ft. per capita or, including tracks, dikes and distribution, 0.5 sq. ft. per capita. The cost of the beds is esti- mated at 15 cents per capita. 1 Experience in the Emscher District has indicated 2 that three- fourths acre of land is required for every 10,000 persons, producing about 30 cu. yds. of spadable sludge (less than 10 per cent, of the volume of the fresh sludge) per annum. One man can handle the sludge from three times the above population if the point of deposit is near the plant. As to the final disposition of the sludge the method selected depends, aside from the cost of land, on the character of the sludge, the material available for sludge beds, the proximity of dwellings and the general character of the actual and pros- pective development in the neighborhood. In general terms, perhaps the following selection, as proposed by Kinnicutt, Winslow and Pratt, is as appropriate as can be given without going into greater detail: 1. In the case of small isolated plants air-drying on the land or in lagoons is generally preferable, giving the dried sludge to farmers or burying it in the ground. 2. For larger, but moderate-sized plants, burying in trenches is found satisfactory. 3. For large cities located on the coast the cheapest and most expeditious method is removal by scow or steamer and dumping at sea. 4. For large inland cities mechanical drying is often necessary, " Rep. on Sewage Disposal." George M. Wisner. Chicago, 1911. 2 Charles Saville, Jour. Assoc. Eng. Soc., July, 1911. 256 SEWAGE SLUDGE in which case the product can be given away as a fertilizer or it can be buried or, in isolated localities, used for filling in land. If these methods of disposal are not feasible for any reason the product can be mixed with house refuse or with a small amount of coal and burned in a destructor. At the present time there are over 330 municipal sewage treatment plants in the United States. Of these, about three- fifths employ the septic tank, either for the complete, or as a preliminary process and one-fifth employ plain sedimentation. The former method, which might more properly be called the semi-septic process, has been very generally adopted in the middle west during the past 10 years. Although the term septic has been popularly attached to these tanks they are not true septic tanks in the light of the Saratoga decision. Their effluents often contain dissolved oxygen and aerobic conditions undoubtedly often exist in those parts of the tank through which the clearer liquid passes, while the solids, detained by efficient baffling and generally collecting largely in the scum by reason of the entrained gas, may at the same time develop septic or anaerobic conditions. The period of retention is generally comparatively brief often not over 4 hours so that the sewage does not become thoroughly putrefactive or devoid of dissolved oxygen before passing off. These tanks and those devised by Travis and Imhoff are similar in this respect and differ from the septic tank of Cameron, where the sewage is retained at least 12, and oftener 24 hours. This, too, is the usual practice in operation in the Eastern states. The divergent results obtained in the former tanks, for which the term "hydrolytic" has been used, from those obtained with the true septic tank has resulted in a certain confusion of ideas in regard to the efficacy and offensiveness of the septic tank pro- cess. The shorter period of retention, combined with a sewage both fresh and weak, results in an almost entire freedom from offensive odors in many of the western plants that is usually not enjoyed where a strong sewage is retained for an entire day in an uncovered tank. So, too, there appears to be a marked difference in the amount of sludge and scum produced; for, as noted by Mr. J. W. Alvord, the deposits, requiring removal from the western plants handling domestic sewage only are frequently very small in amount, while the scum forms rapidly, after septic action is established, to a very considerable thickness. This suggests the desirability of studies to determine the best SUMMARY AND CONCLUSION 257 way of removing and disposing of the scum, which differs materi- ally in character from ordinary sluclge. Although in the Emscher District the scum does not seem to accumulate to a great thickness it may cause trouble in Emscher tanks through its buoyancy by clogging or overlapping the vent openings unless these are of, ample width. By breaking up the scum occasionally with a rake much of it will sink as a deposit with the sludge and release any accumulation of contained gas. \Yhen removed from the surface of a tank receiving fresh sewage and whose contents are not thoroughly septic this scum is not particularly offensive and may often be dried out on beds in the open air before final disposal if not in the immediate vicinity of dwellings. The absence of sulphuretted hydrogen, and objectionable odors generally, in the tanks of the Emscher Association, has been received with a certain amount of incredulity. There appears, with our present knowledge, no good reason why these gases should not form in one style of tank as well as another, provided the other conditions are similar. Possibly the motion of the sludge particles caused by the eruption of gas bubbles and the settlement and withdrawal of sludge may influence the forma- tion of these gases, but it would seem to be largely accounted for by the fact that the greater part of the organic matter from which sulphuretted hydrogen is produced remains in suspension or in solution in the sedimentation chamber and passes out with the effluent, while in the true septic tank these are retained in the tank until putrefaction is energetic and the odors, which are chiefly derived from the non-sedimentable portion rather than from the sludge, are given off in large amounts. With regard to sludge disposal in America, while there are isolated examples of lagooning, drying on the land, centrifuging, pressing and burning, these are so few in number, or else have been carried on with so little knowledge or care for the highest efficiency, that no generalizations can be drawn that would compare in value with those derived from foreign plants and described so fully in the reports of the Royal Commission on Sewage Disposal and by the authors of the first three parts of this volume. The quite common use of the septic tank has, in a measure, simplified the sludge problem and with the anticipated adoption of the Emscher tank by many towns within a short time another step forward will have been taken. Horizontal tanks, 17 258 SEWAGE SLUDGE with or without chemicals, will probably continue to be used on account of local conditions and it is probable that a broader field for fine screening and drying by centrifugals will develop, but from the marked advantages in sedimentation processes carried on in conjunction with a special sludge chamber it seems probable that the Emscher tank in its present or a modified form is destined to play an important part in sewage treatment in America for some time to come. LOCALITIES PAOB Accrington 19, 63 Allenstein ' 78,136 Alliance 233 Andover 211, 217, 248 Aschersleben 132 Atlanta 209 Aylesbury 244 Baltimore 209, 237 Beckum 146 Belfast 128 Berlin 10, 100, 127, 133 Biebrich 60 Bielefeld 136 Birmingham 11, 12, 19, 87, 88, 89, 90, 133, 135, 141, 142, 244 Blackburn 68 Bochum . . : . 145, 164, 173, 177, 179, 181, 182, 183, 185, 189, 226, 229 Bockenheim 93 Bolton 34, 47 Boston 196, 197, 199, 200, 202, 203, 204, 239 Bradford 100, 108, 245 Braunschweig 132, 133 Bremen 18, 33, 57 Brieg 18, 63 Brockton . . . : 209, 242 Brooklyn '. 235 Briinn . 131 Bury 20, 47, 68, 100, 128 California 242 Canton .233 Cassel .... 10, 18, 31, 59, 63, 92, 106, 107, 124, 125, 133, 136, 137, 183 Charlottenburg 10, 17, 43, 45, 48, 100, 124, 135 Chemnitz 70 Chicago 196, 197, 225, 226, 241, 254, 255 Chorley 20, 68 Colchester 68 Cotne 19 Cologne 17,30,38,40,92,126,131 Columbus . . 78, 100, 110, 196, 197, 201, 204, 212, 214, 217, 219, 239, 254 Coney Island 235 Copenhagen 128 Copenick 11,21,28,62,99,127,133 Coventry 244 259 260 LOCALITIES PAGE Culmsee 18, 19 Deutz 104 Dorchester 202, 203, 204 Dresden 17, 104 Dublin 110, 238, 245 Dusseldorf 26 Ealing 68 East New York 235, 236 Edinburgh 123 Elberfeld ... 10, 17, 26, 28, 38, 40, 41, 52, 57, 58, 63, 97, 109, 133, 134 Elbing ; 106 Elmhurst 241 England . . 3, 16, 37, 64, 68, 69, 88, 89, 92, 94, 100, 121, 133, 134, 137, 243, 253 Essen 20, 133, 134, 144, 145, 147, 161, 163, 164, 165, 167, 168, 169, 170, 173, 175, 176, 177, 180, 181, 182, 183, 184, 185, 186, 188, 189, 226, 227 Failsworth 18 Frankfort . . . . 5, 10, 17, 18, 26, 31, 57, 60, 63, 68, 70, 71, 73, 79, 85, 86, 88, 91, 93, 97, 100, 102, 107, 124, 125, 126, 128, 131, 132, 133, 134, 137, 138, 139, 161, 183, 245 Gatow .124 Germany 5, 16, 61, 65, 106, 121, 135, 137, 203 Glasgow 20, 94, 110, 238 Gottingen 136 Guildf ord 20 Guben 52 Halberstadt 19, 20, 57, 62, 63 Halifax 138 Halle ' 66 Hamburg 17 Hampton 19, 135, 142, 147 Hanover 7, 17, 18, 31, 51, 71, 73, 74, 76, 98, 129, 138, 246 Harburg 29, 71, 73, 74, 125, 126, 138, 161, 183 Hendon 20 Heywood 47 Holzwickede 177 Huddersfield 99, 133 Hyde 128 Insterburg 136 Karlsruhe 28 Kingston 94, 123 Konigsberg 133 Langensalza 18, 63, 132 Lawrence 196, 197, 210, 217 Leeds 12, 23, 63 Leipzig '.' 6, 17, 18, 19, 20, 23, 56, 57, 60, 91, 109, 124, 137 LOCALITIES 261 PAGE Litchfield 20 London 6, 15, 20, 110, 128, 129, 238 Luttich 125, 183 Madison 219 Mairich 45, 52, 132, 134 Manchester 12,19,88,89,110,126,127,128,129,142,238 Mannheim 10, 18, 31, 51, 57, 70, 85, 86, 88, 89, 91, 135 Mansfield 221,240 Marburg 17, 26 Massachusetts 197, 242, 246 Merseburg 19, 20, 26, 52 Munich-Gladbach 17, 18, 28, 31, 51, 63 Mulheim-Ruhr 142 Mullheim 19, 63 Neustadt 45, 50, 91 Neustrelitz 62 New Brunswick 209 New York 241, 246 Norwich 142 Oberschonenweide 67, 104, 105 Ohrdruf 17, 52, 63 Oldham 126 Oppeln 52 Osdorf 10 Paterson 197 Paris 7 Pawtucket 210, 221 Pforzheim 128 Philadelphia. . . .196, 197, 206, 214, 224, 226, 240, 246, 247, 250, 253 Plainfield 197, 210, 217, 221 Potsdam 94, 98, 99, 127, 137, 138 Providence 197, 209, 232, 239, 243 Queens 241 Rauxel 146 Reading 206, 207, 217, 240, 245 Recklinghausen . . 59, 92, 135, 144, 154, 155, 157, 158, 161, 164, 170, 173, 175, 177, 179, 180, 183, 185, 189, 226 Remscheid 132, 133, 134 Rheydt 24 Rochdale 63 Salford 11, 128, 129, 238 Saratoga 223, 256 Schoneberg 17 Sheepshead Bay 235 Sheffield 12, 20, 21 Siegen 24, 52 Skegness 78 Southampton .... 110, 238 262 LOCALITIES PAGE Spandau 66, 70, 99, 137 Stargard 18 Stuttgart 19, 63, 98, 102 Tegel 102, 137 Thorn 39 Torgau 91 Unna 12, 19, 24, 63, 92, 142 Washington 254 Waterbury . 196, 197, 202, 209, 222, 239 White Plains ! 234, 24f) Willesden 68 Wimbledon 68, 133, 134 Windsor 244 Worcester 196,197,200,212,230,243,247,249 LIST OF NAMES PACK Alvord . 256 Ashton 129 Barwise 12 Bechold 125, 121 Beck 106 Belcher 254 Bemmelen, van 133 Blunk 164, 165, 172, 228, 255 Bosley % 237 Bowles . . . 219 Bredtschneider 97, 127, 131 Brown 204 Bujard 127 Busing 16 Butschli, von 133 Cameron 256 Carpenter 210 Clapp 232 Crimp 244 Davis 219 Degener 106, 127 Dost 98, 104, 127 Dunbar 27, 68, 131, 133, 135, 140 Egestorff 71 Eisner 227, 252 Favre . 183 Fellner 93 Fidler 47 Frank 127 Friedrich 126 Fuller 196, 197, 198, 212, 243 Gault 201 Gavet 197 Geiger 28 Gohring '.127 Gregory 227, 229 Grimm 39, 49 Grosse Bohle 126, 131 Grossmann 126 Haack . . 125 Haubold 70 Heine 126, 127 263 264 LIST OF NAMES PAGE Henkel 106 Hering 227 Herzberger 128 Honig 137 Hopfner 124, 125 Horsfal 128 Imhoff 64, 131, 132, 147, 172, 224, 229, 256 Jackson - 220, 236 Johnson 197, 212 Kinnicutt, Winslow and Pratt 197, 200, 217, 239, 246, 255 Kolle 128 Koschmieder 96, 104, 127 Krupp 166 Kubel 156 Kuichling ? . . . . 202 Lacombe 125 Lathbury-d'Olier 245 Liibbert 140 Metzger 117, 121 Middeldorf 147 Paulmann 124, 125 Pearse 225, 255 Phelps 199, 200 Poschl 133 Powers 234, 235 Proskaner 97 Reischle 69, 73, 77, 98, 104, 125, 127, 138, 161 Reuther 51 Rideal 244 Rothe . 98 Rothe-Degener 127 Rothe-Rockner 134 Ruggles 239, 243, 244, 246 Saloman 40, 124, 132, 133, 136 Saville 227, 241 Schaefer-ter Meer 71, 244 Schiele 69, 94, 128, 131 Schmeitzner 27, 70 Schonfelder 38, 40 Schreiber 10 Schury 127 Schwerin, von 79, 139, 177 Scotland 123 Snow 242 Spillner 79, 165, 172, 178, 179, 183, 185, 186, 227, 228, 255 Steuernagel 14 Taylor 209 Thiesing 69, 73, 77, 125, 138, 161 LIST OF NAMES 265 PAGE Thumm 131 Tillmans 80, 131, 139 Travis 49, 135, 142, 147, 256 Uhlf elder 128 Ulrich 208 Voelcker 242 Voss 125, 126 Wattenberg 147 Weand 206, 207, 208 Webster 197 Wegner 52 Whipple 197, 198 Winslow 200 Winter 164 Wisner 225, 246, 254 Ziegler 93 INDEX ABC Process (See also Chemical Precipitation), 94, 123, 244 Acreage required (See Area, Sludge Beds, Sludge Drying, Sludge Burial.) Aerobic (See Bacteria.) Agricultural use (See Fertilizer.) Air (See Compressed Air.) Albuminoid Ammonia, 211, 230, 232 Alum, Alumina (See Sulphate of Alumina.) Alumino ferric, 68 Ammonia, 140 Anaerobic (See Bacteria.) Analysis (See Sludge Composition, Sewage.) Angle (See Slope.) Area (See also Sludge Beds.) for sludge beds, 109, 166, 240, 254, 255 for sludge disposal, 88-, 89 Bacteria, 24, 79, 160, 164 aerobic, 140 anaerobic, 140 pathogenic, 24 Bacteria beds (See Contact Beds.) Baffle, 215, 224, 225, 256 Belloform, 132 Benzine, 107, 125 Boston Main Drainage, 200, 239 Briquettes, 80, 93, 97, 99, 100, 102, 127 Broad irrigation (See Irrigation.) Bubbles (See Gas.) Burial (See Sludge Burial.) Burning, disposal by, 94, 95, 99; sludge, 100, 114, 128, 241, 242, 244, 245, 249, 250, 251, 257 (See also Sludge, Calorific Value.) Calorific value (See Sludge, Cal- orific Value.) Candy system, 47 Carbon dioxide (See Carbonic Acid.) Carbonic acid, 97, 101, 143, 191, 247, 248 Carriage, Carting (See Conveyor, Channels, Pipes, Transpor- tation, Wagon.) Cellulose, 125 Cement, 99 Centrifugal machine, 69, 112, 113, 129, 137, 138, 142, 208, 244 258 Centrifuged sludge, 100, 106, 138, 161, 208 257 Cesspool, 52, 85, 190, 237 Channels, 50, 53, 61, 85, 86 Chemical precipitation, 10, 20, 21, 115, 133, 135, 230, 243, 244 sludge, 67, 84, 104, 230, 244, 252, 253 tank, 232, 233, 235 Chicago Sanitary District, 225, 254 Chlorine, 235 Cinders (See Slag.) Clay, 109 Cleaning tanks, 13, 15, 31, 33, 34, 48, 217, 233 (See also Re- moval.) Cleaning grit chambers, 22, 52 Cleaning screens, 204, 207 Clinker (See Slag.) Coal, 97, 98, 100, 104, 114, 127, 190, 235, 241, 248, 249, 250, 251 Coke, 165, 248, 249 Colloids, 39, 79, 132, 141 Combustion (See Burning, Gas, Sludge-Calorific Value.) 267 268 INDEX Composition (See Detritus, Gas, Screenings, Scum, Sewage, Sludge.) Compost, 92, 136 Compressed air, 49, 51, 52, 66, 87 Conduits (See Channels, Pipes.) Contact beds (See Filtration.) Conveyor, 52, 76, 80, 207, 245 Copperas, 230 Cost (See Process in Question.) Crops, 237, 238, 242 Decomposition (See Digestion.) Delivery (See Conveyor, Channels, Pipes, Transportation, Wagon.) Deodorant, 60 Detritus (See also Screenings.) from grit chambers, 8, 22, 83, 92, 115, 199 amount, 17, 200, 201, 202 Digestion of sludge, 11, 14, 78, 112, 140, 141, 143, 160, 177, 178, 182, 191, 218, 219, 226, 227, 228, 247 Dilution of sludge, 74 Disinfectant, 7 Disinfection, 235, 236 Distillation of gas, 101, 248, 249 of grease, 104, 107, 108, 248 Distribution (See Sludge-Transpor- tation.) Dortmund tank, 37, 39, 48, 252, 254 Drainage water, 151, 152, 156, 157, 159, 160, 169, 178, 188, 191, 250 Dredge, 26, 34, 50 Drying beds (See Sludge Beds.) Dumping at sea. (See Ocean Dis- on land (See Filling in Land.) Ejector (See Steam Ejector, Shone Ejector.) Electro-osmose, 79, 139 Emscher tank, 14, 19, 39, 42, 45, 53, 59,63,79,99,112,116,143, 147, 177, 178, 180, 183, 191, 224, 243, 255, 257, 258 sludge, 62, 143, 159, 160, 179, 224, 241, 243, 252, 253 cost of, 189, 254 Enzymes, 160, 164 Essen tank (See Emscher Tank.) Facilol, 60, 132 Fats (See Grease.) Fermentation (See Digestion.) Ferric sulphate, 230 Fertilizer, 3, 5, 6, 55, 80, 83, 84, 85, 89, 91, 92, 107, 108, 114, 123, 125, 126, 170, 177, 183, 184, 233, 235, 236, 242, 246, 252 Fidler system, 48 Filling in land, 83, 109, 170, 231, 240, 252, 256 Filter pressing (See Sludge Pressing.) Filters, intermittent, 78, 113, 140, 230, 242 contact, 4, 12, 19, 27, 57, 74, 78, 112, 113, 140, 252 sprinkling, 4, 19, 57, 141, 208, 252 drum, 137 roughing, 141 Flies, 59, 60, 85, 92 Floating arm, 28, 230 Flow, 31, 32, 42, 45, 53, 178, 190, 225 Flushing, 32, 42, 45, 53 Fresh sludge (See Sedimentation, Sludge.) Gas (See also Odors), 12, 25, 39, 57, 78, 79, 95, 96, 97, 101, 127, 141, 146, 153, 176, 177, 179, 182, 183, 184, 187, 191, 202, 217, 224, 225, 227, 247, 256, 257 composition, 102, 105, 143, 161, 225, 248, 249 calorific value, 102, 103, 105, 114 Gels (See Hydrogels.) Globe fertilizer, 94 Gradient (See Slope.) INDEX 269 Grease, 230 in scum, 216 in sewage, 4, 25, 84, 106, 113 in sludge, 10, 24, 36, 41, 67, 70, 73,91,95,97,100,106,113, 114, 125, 183, 248 value, 108, 126 Grit, Grit chamber (See also De- tritus), 8, 19, 22, 52, 78, 165, 180, 200, 201, 202, 204, 225, 252, 253 Ground water, 230, 233 Heat (See Burning, Calorific Value.) Hille's process, 244 Hydrogels, 133, 160 Hydrogen sulphide (See Sulphu- retted Hydrogen, Odor.) Hydrosols, 132 Illuminating power, 102 Imhoff tank (See Emscher Tank.) Incineration (See Burning.) Infiltration to sewer (See Ground Water.) Intermittent filtration (See Filtra- tion.) Iron salts as precipitants, 68, 137 Irrigation, 12, 74, 83, 88, 90, 112, 113, 114, 132, 133, 140 Kremer apparatus, 10, 24, 36, 43, 45, 48, 61, 84, 108, 109, 116 Lagoons (See Sludge Beds.) Land (See Acreage, Filtrati on , Irriga- tion, Filling in Land.) Lignite process, 11, 21, 44, 45, 47, 62, 67, 69, 70, 98, 100, 104, 115, 127, 133, 137 sludge, 94, 99, 105, 138 Lime precipitant. added to sewage, 10, 20, 84, 106, 109, 135, 230, 232, 233, 235, 236, 244 added to sludge, 3, 59, 60, 68, 69, 70, 84, 92, 94, 99, 137, 230, 231, 233, 242 Loam, 109 Manganese dioxide, 235 Marsh gas (See Methane.) Massachusetts Institute of Technol- ogy Experiments, 199, 202 Massachusetts State Board of Health, 210, 217, 230, 247 Methane, 140, 143, 179, 191, 247, 248 Metropolitan Sewerage Commission, Boston, 204, 205 of New York, 214, 229, 235 Micells, 133 Moisture in sludge (See Sludge- composition.) Montejus, 106 Native Guano, 94, 123 (See also Fertilizer.) Night soil, 5, 85, 236 (See also Fertilizer.) Nitrates, 140, 152, 156, 188 Nitrites, 140, 152, 156, 188 Nitrogen, 6, 83, 84, 85, 93, 114, 169, 183, 242, 247, 248, 249 Nuisance (See also Odor, Flies), 3, 121, 125, 256 Ocean disposal of sludge, 5, 6, 110, 128, 238, 255 Odor, 5, 11, 31, 36, 52, 56, 59, 60, 61, 67, 69, 77, 79, 80, 85, 88, 92, 93, 94, 101, 109, 129, 132, 134, 135, 136, 141, 152, 159, 179, 183, 190, 191, 217, 222, 225, 227, 237, 240, 252, 256, 257 Odorless excavator, 237 Oxygen, 101, 256 Pathogenic germs (See Bacteria.) Peat, 59, 60, 92, 98, 102, 114, 127, 132, 248, 249, Perchloride of iron, 235, 236 Phosphates, Phosphoric acid, 83, 93, 242, 248 (See also Fertilizer.) Pipe (See also Transportation, Flow), 42, 47, 49, 52, 53, 61, 85, 86, 227, 252 Plowing under (See Sludge Burial.) 270 INDEX Pneumatic (See Compressed Air, Odorless Excavator, Sludge Transportation, Vacuum Receiver.) Population (See City in Question.) Potash, 83, 84 Poudrette, 93, 125 Power required, 76 Precipitant (See Alumino-f erri c, Chemical Preci p i t a t i o n, Ferric Sulphate, Iron Salts, Lignite, Lime, Sulphate of Alumina.) Pressed sludge (See Sludge Cake.) Pressing sludge (See Sludge Pressing.) Pump, pumping sewage, 225 sludge, 41, 50,' 51, 66, 87, 135, 146, 230, 233, 235, 237 detritus, 26, 27, 210 Putrefaction, 7, 14, 25, 59, 76, 135, 143, 169, 180, 236, 256, 257 Recovery (See Fertilizer, Gas, Grease, Calorific Value.) Removal of detritus from grit chambers, 22, 25, 201 from screens, 23 of sludge, 22, 129, 242 from plain precipitation, 23, 27, 47, 48, 215, 217 from chemical precipitation, 235 from Emscher tanks, 23, 143, 170, 174, 227 from septic tanks, 23, 218, 221, 222, 223 Retention (See Removal.) Revenue (See Sludge, Value of.) Roily water (See Turbid Liquid.) Rotary dryer (See Centrifugal Machine.) screen (See Screen.) Rothe-Rockner process, 134 Royal Commission of Sewage Dis- posal, 238, 242, 244, 257 Experiment Station, Berlin, 16, 128 Salt, 235 Sand (see also Filtration, Detritus), 24, 26, 109, 241 Sand filters (See Filtration, Inter- mittent.) Sawdust, 241 Scraper, 45, 47, 73 Screw conveyor (See Conveyor.) Screen, screening: bar, 19, 22, 51, 84, 115, 202, 203, 204, 209, 210, 221, 225, 233, 235, 252 mesh, 22, 76, 84, 115, 200, 204, 206, 208, 209, 245, 252, 258 Screenings, 9, 92, 202 composition, 9, 204, 205, 209, 210, 245 amount, 17, 19, 204, 205, 209, 210, 245, 253 Scum, 110, 141 composition, 216, 224, 225 amount, 215, 216, 222, 224, 227, 256, 257 disposal, 126 Scum board, 29, 141, 215, 252 Sea discharge (See Ocean.) Sedimentable matter, 190 Sedimentation (See also Precipita- tion.) plain, 15, 18, 30, 190, 210, 212, 213, 256, 258 tank, 40, 46, 62, 115, 133, 140, 141, 142, 212, 214, 217, 257 sludge, 62, 64, 78, 83, 102, 131, 132, 214, 217, 241, 252, 253 Septic tank (See also Sedimenta- tion, Sludge), 11, 25, 74, 79, 84, 115, 140, 141, 142, 217, 219, 221, 222, 223, 247, 252, 253, 254, 256 Settling (See Sedimentation.) Sewage, composition, 8, 11, 16, 20, 195, 196, 197, 198, 199, 206, 211,212,213,218,220, 221, 222, 223, 226, 231, 234, 236, 247 Shone ejector, 230 Shutters, 50 Siphon, 47, 53, 154 Skimmer, 44, 45 Slag, 99, 101, 109, 152, 164 INDEX 271 Slope of bottom, 30> 31, 37, 38, 39, 40, 41, 43, 49, 50, 224 of pipe, 49, 53 Sludge bed (see also Sludge Dry- ing, Area), 56, 57, 59, 63, 87, 90, 112, 134, 136, 137, 147, 152, 159, 164, 165, 175, 177, 188, 191, 235, 237, 240, 241, 243, 250, 254, 255, 257 burial, 88, 135, 142, 233, 239, 243, 255 (See also Area, Sludge Drying.) cake, 67, 94, 99, 100, 106, 107, 108, 231, 233, 244, 252 calorific value, 95, 96, 98, 100, 102, 104, 127, 152, 246, 249, 250, 251, 252 (See a Iso Burning.) composition, 7, 9, 10, 11, 12, 13, 14, 16, 36, 43, 54, 61, 74, 84, 89, 91, 122, 131, 144, 145, 146, 148, 149, 151, 153, 154, 158, 159, 161, 167, 168, 175, 180, 181, 184, 185, 212, 214, 215, 217, 218, 221, 222, 223, 224, 226, 242, 247, 250 cylinder, 43 distribution (See Pipe Lines, Channels.) drainage of, 3, 41, 56, 91, 134, 137, 142, 146, 160, 163, 164, 176, 178, 186, 188, 191, 241 (See also Sludge Drying, Sludge Beds.) drying, 55, 128, 129, 132 artificial, 64, 94, 104, 122, 138, 244, 252, 255, 257, 258 in the air, 6, 21, 24, 30, 36, 56, 60, 61, 62, 67, 80, 90, 93, 97, 98, 107, 109, 122, 133, 140, 156, 176, 212, 224, 227, 228, 235, 240, 241, 244, 245, 252, 254, 255, 257 freezing, 176 grease in (See Grease.) holder (See Sludge Receiver, Sludge Tank, Vacuum Re- ceiver.) liquefaction (See Digestion.) liquor (See Turbid Liquid.) removal (See Removal.) measuring, 173, 175 press, 18, 65, 77, 106, 108, 113, 127, 137, 142, 230, 232, 233, 243, 244, 252, 257 pushing car, 33, 34 receiver, 66, 72, 78, 86, 87, 110 sampling, 184 specific gravity (See Sludge Composition, Weight.) septic tank, 61, 62, 64, 91, 92, 98, 102, 103, 110, 140, 141, 142, 247, 248 steamer (See Sludge-Transpor- tation, Ocean disposal.) storage of, 85, 113, 140 (See also Digestion, Removal.) tank, 207, 230 transportation, 6, 51, 59, 76, 85, 91, 110, 124, 129, 231, 232, 237, 238, 239, 241 value of, 82, 84, 89, 91, 92, 99, 123, 124, 126, 129, 170, 242, 243, 244, 245, 246 volume, 5, 7, 10, 12, 13, 14, 15, 19, 54, 61, 64, 70, 73, 74, 77, 82, 90, 102, 104, 112 124, 126, 166, 253 from plain sedimentation 102, 132, 211, 212, 213, 214, 234 from septic tanks, 19, 219, 220, 222, 252, 256 from Emscher tanks, 144, 148, 150, 161, 162, 163, 165, 167, 168, 173, 176, 177, 221, 224, 225, 226, 227, 228, 229, 252 from chemical precipitation, 20, 230, 232, 233, 234, 235, 236, 240 weight, 76, 102, 148, 150, 151, 155, 158, 166, 167, 168, 223, 231, 244, 250, 253 Smell (See Odor.) Solids in sewage (See Sewage- composition.) in sludge (See Sludge-compo- sition.) 272 INDEX Sprinkling filter (See Filtration.) Squeegee, 34, 35, 47 Steam ejector, 26, 52 Stirring device, 44, 45, 47, 66 Storage (See Removal.) Storm water, 8, 20, 191 Street wash (See Storm Water.) Sulphate of alumina, 69, 98, 104, 127, 133, 230, 244 Sulphide of hydrogen. (See Sul- phuretted hydrogen.) (See also Nuisance, Odors.) of iron, 94, 134, 141, 221 Sulphuric acid, 106, 108, 235 Sulphuretted hydrogen, 79, 140, 143, 156, 169, 179, 257 (See also Odor.) Sump, 29, 42, 50, 51, 53, 78 Suspended matter (See Sewage- composition, Sludge-com- position.) Sweepings, 92, 93, 100, 114, 128, 136 Tank (See Candy T., Chemical Precipitation T., Dortmund T., Emscher T., Kremer Apparatus, Septic T., Sedi- mentation T., Sludge' T.) Temperature, 227, 247, 250 Towers, 14, 27, 45, 127, 134 Trade waste, 206, 232, 252 Transportation (See Carts, Con- veyors, Channels, Pipes, Sludge Transportation.) Turbid liquid, 27, 29, 36, 38, 48, 49, 50, 51, 57, 78, 85, 139, 186, 187, 188, 230, 241 Under-drainage (See Drainage Water, Sludge Drainage.) Utilization of sludge, agricultural (see Fertilizer), burning (see Calorific Value) (Burning), production of gas (see Gas), recovery of grease (see Grease.) Vacuum receiver, 18, 27, 29, 41, 42, 51, 52, 78 Valves, 23, 28, 29, 48, 49, 51, 53, 72, 86 Velocity, 14, 30, 200, 201, 202, 212, 215, 233 Vermin, 125 Viscosity, 160 Vitriol (See Sulphuric Acid.) Volume of sludge (See Sludge.) of scum (See Scum.) Wagon, 52, 85, 129, 237 Wastes (See Trade Waste.) Water in sludge (See Sludge Com- position.) Wells (see also Sump), 14, 27, 29, 36, 37, 39, 45, 47 ERRATA Page 16. Line 2 from bottom. In place of "suspened" should read "suspended." " 19. Line 4. In place of " 100 " should read " 1000." " 23. Line 15. In place of " very " should read " every." " 27. Reverse the numbers and positions of footnotes. " 55. Under Fig. 20. In place of "the watering" should read "De- watering." " " Last word. In place of "incineration" should read "evapora- tion." " 56. Line 12. In place of "presser" should read "presses." " 62. Line 4. In place of "2 to 3 to 1 to 2" should read "2/3 to 1/2." ' 74. Line 8. In place of " 2 to 3 " should read " 2/3." Line 9. In place of " 1 to 3 " should read " 1/3." " " Line 12 from bottom. In place of "9 to 10" and "1 to 10" should read "9/10" and "1/10." Line 15. In place of " 1720" should read " 1718." " 109. Line 10. In place of "withe" should read "with." " 135. Line 5 from bottom. In place of "W. Oven Travis" should read "W. Owen Travis." " 148. Line 2 from bottom. In place of "1.9 " should read "91." " " Line 1 from bottom. In place of " 2.1 " should read "21." " 183. Line 15 from bottom. In place of " Rechlinghausen " should read " Recklinghausen." " 200. Line 7. in place of "were" should read "was." " 201. Line 2. In place of " 18,150" should read " 1815." " 204. Line 1 from bottom. In place of "Com'rs" should read "Com'n." " 210. Line 13. In place of "pumpted " should read "pumped." " 219. Place Table XVI at foot of page. " 225. Line 8. In place of " 40 " should read " 400." " 239. In Table XXIX indent " Barking " instead of " Glasgow." " 244. Line 10 from bottom. In place of "the Hilles" should read " Hille's." " 12 4 251. Lines 3 and 4 from bottom in column 2. In place of ' should read " 12.4-22.9." " 255. Line 13. In place of " 10 " should read " 1.0." ALLEN'S SEWAGE SLUDGE. RETURN TO the circulation desk of any University of California Library or to the NORTHERN REGIONAL LIBRARY FACILITY Bldg. 400, Richmond Field Station University of California Richmond, CA 94804-4698 ALL BOOKS MAY BE RECALLED AFTER 7 DAYS 2-month loans may be renewed by calling (510)642-6753 1-year loans may be recharged by bringing books to NRLF Renewals and recharges may be made 4 days prior to due date DUE AS STAMPED BELOW FEB 2 1 1995 20,000 (4/94)