LIBRARY UNIVERSITY OF CALIFORNIA. Deceived J rL$/l'. * , i8qO , ^Accessions No.*2. /^/^f~ /. Class No. --------------- i ....... A DISCUSSION OF THE PREVAILING THEORIES AND PRACTICES RELATING TO SEWAGE DISPOSAL BY WYNKOOP KIERSTED, C.E., Member of American Society of Civil Engineers. FIRST EDITION. FIRST THOUSAND. NEW YORK : JOHN WILEY & SONS, 53 EAST TENTH STREET. 1894. WYNKOOP KIERSTED. PREFACE. THIS discussion of questions relating to sewage dis- posal is prompted by reason of the disregard with which these questions have been treated in this country until very recent years, and the prominence lately given to the method of sewage disposal by land. It deals rather with the principles embraced in the prevailing methods of sewage disposal than with methods of mechanically treating sewage. The more thoroughly these questions are discussed the more generally will they be understood and the more speedily effectual will become the efforts that are directed to the devising of practicable methods of finally and inoffensively disposing of the sewage of populous districts. We have in nature conclusive evidence of the exist- ence of a natural process of purification of polluted IV PREFACE. waters. This process is of such a character that it can be utilized in the purification of sewage ; and with our present methods of sewerage and drainage it must be- come the foundation of any successful method of sew- age disposal. The author's aim in this discussion is to set forth this natural process of purification together with the various considerations embraced in questions of sewage dis- posal in a simple and practical manner. CONTENTS. PAGES INTRODUCTION vii-xiv CHAPTER I. SEWAGE AND SEWERAGE ....<,. 1-13 CHAPTER II. VITAL PROCESS OF PURIFICATION ...... 14-26 CHAPTER III. DISPOSAL BY DILUTION , . 27-81 CHAPTER IV. DISPOSAL BY IRRIGATION ....... 82-102 CHAPTER V. DISPOSAL BY INTERMITTENT FILTRATION .... 103-137 CHAPTER VI. PURIFICATION OF SEWAGE BY CHEMICAL PRECIPITATION . 138-146 CHAPTER VII. GENERAL DISCUSSION .... = .. 147-174 INTRODUCTION. IN nature there is a great storehouse of energy, a beautiful exhibition of harmonious motion among countless bodies, and a wonderful mani- festation of balanced forces. We observe there that laws are few, simple, and immutable. The energies, forces, and processes of nature may be utilized by man in various ways, and the extent to which man can direct them to his own ends is a measure of his intellectual and material advance- ment. Philosophers and scientists have labored to develop and establish the principles involved in natural laws, and to formulate them in a manner to be attainable by all. With every new facility for analyzing nature they have discovered some new principle of life or of force which serves to Vlll INTRODUCTION. correct errors in theories that may have been previously formulated upon a partial knowledge of natural law or upon imperfect observations of natural phenomena. The formulated results of their researches have frequently been termed im- practicable theories ; yet they are at the foundation of substantial advancement in the arts, of the productive application of natural processes and forces, and of prosperity and wealth in the ordi- nary affairs of life ; and they are becoming more and more to be so understood and to be propor- tionately appreciated. It may therefore be ex- pected that the results of the scientific researches now in progress will inspire far greater confi- dence than formerly among people generally, with regard to the applicability of these results to useful and practical purposes. In fact it is just such a confidence and appreciation that is most needed to stimulate investigators and others to even more energetic efforts than heretofore in the development of a practicable science. Nature never fails to reward a searcher in her storehouse of riches ; and any investigator re- INTROD UCTION. IX lying upon the unswerving stability of natural law, upon the steady balance and interchange- ability of energy and force, and upon the positive sequence of cause and effect, can be assured of connecting any observed phenomenon in nature, no matter how singular or exceptional, by a chain of convincing evidence in line with natural law, with some prime natural cause. And any truth or principle of nature thus estab- lished is of value, for it is always of some practi- cal utility. But it is seldom that the scientist and the phi- losopher, the discoverers and developers of nat- ural laws, principles, forces, and processes, are the ones to practically apply the results of their own efforts. This frequently and generally falls to the lot of others, middlemen as they may be called, who weigh these results and determine the range of usefulness. Among these middlemen engi- neers may be classed, who, by admitting that a study and knowledge of natural law and force is essential to the intelligent and economical appli- cation of the involved principles, and by ac- X INTRODUCTION. cepting the consistencies and the science of nat- ure, have elevated their occupation from a mere trade or art of directing men and handling ma- terials to a profession that is closely connected in various ways with many departments of science. They give material and productive form to the deductions of natural science. Their education and training should develop such a capacity and a desire for scientific studies, that they may be among the first to group and ana- lyze the results of scientific research, and may possess a skill to properly apply these results in practice. They cannot consistently permit their conservatism and their almost constant contact with material things to divert their interest and sympathy from the scientific part of engineering, nor to bias their judgment regarding the results of scientific research when accompanied by reason- ably conclusive evidence of its truth and value. Thus the mutual dependence of the depart- ments of natural science and practical engineer- ing becomes so intimate as to invite a respect- ful cooperation of the workers in both de- INTRODUCTION. XI partments, in order that the results of their com- bined efforts may be the more speedily directed to useful purposes. But it is not enough that reciprocal efforts should be confined alone to these two classes of workers, for it is necessary that the public, which is yet not altogether free from scepticism regarding scientific discoveries, but upon whom to a great extent must depend the fulness and rapidity with which such discov- eries can be applied, shall be brought to see and appreciate their merit and utility. Such an understanding and appreciation, at least with regard to matters of sanitation, might perhaps be rendered the easier if the laws, the principles, and the processes of nature, as they affect the customs and health of people in com- munities and assemblages, should be more gen- erally and specifically taught in the schools, oftener discussed by the press, more precisely and popularly treated in current literature, and generally made more familiar topics. In this connection it may be noted that the accumulating and convincing evidence of the re- Xll INTROD UCTION. lation of the vital activity of living organisms to the decomposition of organic matter, together with the almost constant publicity which this rela- tion and its accompanying evidence is receiving, renders it one of the most generally accepted of the newly developed processes of nature. We now believe that by this process all de- composable and putrescible matter may be trans- formed into other and more stable compounds, and that all organically polluted waters may be purified. In all probability many of the troubles expe- rienced with public water-supplies and with sew- age have been, and still are, due to a disregard or misunderstanding of the principles involved in natural processes of purification. In fact there is probably no branch of engineering that re- quires a more general and thorough knowledge of natural laws, principles, and processes, and a greater skill in the application of these to useful purposes, than does that branch which appertains to the selection and development of water-sup- plies and to sewage disposal. INTRODUCTION. xiii In the discussion contained in the succeeding chapters it is admitted that the vital activity of living organisms is primarily responsible for the decomposition and destruction of organic matter, as such, in polluted waters ; that this vital pro- cess in its completeness is a provision of nature to maintain the purity of the elements which support life ; that observation and study of the conditions in nature which affect this process are essential to its proper application ; and that the application of this natural process to the purifi- cation of such a grossly polluted and polluting matter as sewage should observe, with a proper margin of safety, the limitations that nature has placed upon it. It regards sewage disposal as admitting of the fullest discussion, because it is only of recent years that the population of cities in the United States has become sufficiently dense to feel the serious effects of careless and temporizing methods of sewage disposal, and be- cause the greatly diversified conditions in this country require a more or less modified applica- tion' of the experiences in foreign countries. X l v IN TROD UCTION. Moreover, it regards the results of experiments of the Lawrence Experimental Station in Massa- chusetts as authoritatively instructive regarding the principles involved in the natural process of purification of polluted water, and the author does not hesitate to frequently refer to the reports of the State Board of Health, under whose directions these experiments have progressed, and to freely quote from the pages of these reports. SEWAGE DISPOSAL. CHAPTER I. SEWERAGE AND SEWAGE. RECORDS of drainage works of considerable magnitude date back to the early centuries of the Christian era. Notwithstanding the fact that we possess but meagre and indefinite descriptions of these works, there remains enough of the works themselves to demonstrate a regard of the an- cients for systematic drainage. However far sanitation as a science may have advanced at that early period, it began, we are informed, during the decline of the Roman Em- pire, so to decay that in the Middle Ages when 2 SEWAGE DISPOSAL. civilization had apparently retrograded, when barbaric customs had supplanted hygienic observ- ances, when crusades, feudal strifes, and political disturbances had hindered the advancements of nations in peaceful pursuits it had few if any votaries. Modern sanitary science attributes some, at least, of the devastating plagues of that early day to the neglect of observing proper and hygienic methods of living. It was not until after the beginning of the present century that the modern systems of drain- age and sewerage began to be developed. It is easy to conceive that the introduction of water under pressure as a public supply so prompted and encouraged a liberal use of water for all do- mestic and industrial purposes that the necessity arose for a method of house-drainage that would quickly and effectually remove soiled water from the premises. It was but natural to discharge this soiled water into any street drains that may have been in use to remove storm-water, inas- much as excrementitious matter was removed by methods that were independent of the system of SEWERAGE AND SEWAGE. 3 public drainage. But the convenience of water under pressure within the dwelling, and the ease with which it could be utilized to remove waste matter, gradually led to the introduction of toilet- room fixtures and to improved facilities of house- drainage connecting with cesspools. Of this practice in London, Sir J. W. Bazal- gette wrote that "up to about the year 1815 it was penal to discharge sewage or other offensive matter into sewers." Doubtless at that time the experience in London demonstrated what a later experience in many other cities has proved, that an accumulation of filth in cesspools about the premises is a menace to health, and that sanitary regulations require a prompt and complete re- moval of excrementitious matter. As a matter of expediency it was permitted to enter the pub- lic drains ; but when once the safety and practi- cal utility of this practice became established, then followed the enactment of laws and regu- lations making it obligatory to discharge excre- mentitious matter into the public sewers, and thus officially recognizing one of the first princi- 4 SEWAGE DISPOSAL. pies of modern sanitation, namely, the prompt, rapid, and complete removal of filth from all hab- itations ; and originating the " water-carriage " system of sewerage. So in London " in the year 1847 the first act was obtained making it com- pulsory to drain houses into sewers." Somewhat later the " water-carriage " system of sewerage became developed into the "com- bined" system, which provides sewer capacities for the united drainage of storm-water and all domestic and industrial waste ; and into the " separate " system, which provides sewer capaci- ties for sanitary drainage and for a portion of storm-drainage from roofs, yards, and courts. In order that the pipes and drains comprising a system of sewerage and drainage might be in as perfect accord as practicable with the essentials of proper sanitary drainage, it became necessary to adopt such sectional forms of sewers, such limiting gradients, such methods of ventilation, flushing, and construction, and such restrictions with respect to the intoduction of solid and in- soluble refuse into sewers, as would insure a ve- SEWERAGE AND SEWAGE. 5 locity of flow, a circulation of pure fresh air, and a continuity of movement within the sewer, that would serve to prevent deposits, putrefactive changes, and offensive gases therein. The prin- ciples and rules of guidance in matters of this kind are already so well outlined in various pub- lications as to need no elucidation here ; in fact any effort in that direction would be quite for- eign to the objects of this discussion. With respect to the two systems of sewerage, no valid claim can be made of the general adapt- ability of either system to the exclusion of the other. The varying physical conditions of any territory to be drained and the economic aspects of the questions at issue must decide in each case whether the system of sewerage should be the "combined," the " separate," or a combination of the two systems. So far as concerns the sanitary conditions which may prevail within the sewers of either system, the sewers of each having had bestowed upon them equal skill in design and construction, they are shown by experience to be equally good. The mere application of a few 6 SEWAGE DISPOSAL. principles to the design of sectional forms and capacities of sewers is now so well defined as to become a comparatively simple process. Indeed questions of design are of less importance than the more complicated ones relating to the adap- tation of a system of sewers to the natural con- ditions of any locality. These questions involve considerations of a present and future disposal of sewage, which, in turn, are affected by various conditions, both natural and artificial, that inde- pendently or in combinations may have a diver- sified bearing and may lead to very dissimilar conclusions in different localities. It is not usual that the inception and construc- tion of the first sewerage works of most cities involve comprehensive plans of main drainage and sewage disposal ; for such works very often continue to progress regardless of many of the requirements of a comprehensive system, until the commercial and industrial interests of the city shall have become so developed and estab- lished as to admit of an intelligent study of such problems and a definite outline of such plans. SEWERAGE AND SEWAGE. 7 Even then various artifices and makeshifts are frequently resorted to in order to postpone, for as long a time as possible, expenditures of money in a public improvement, which, though evi- dently needed for the public good, is non-pro- ductive of revenues. In short, complete main- drainage and sewage-disposal works in almost any city are the result of a process of evolu- tion through various stages of development, re- quiring in many instances more or less modifica- tion or abandonment of previously constructed works. Sewage is a complex mixture with water of the various waste products of life and industry from densely settled communities, of which the solids are properly restricted to those that are suscepti- ble either of solution in water or of becoming speedily disintegrated while in a state of transit. The measure of the volume of any dry-weather flow of sewage is practically the volume of the water consumed by that part of the community connected with the sewers, frequently somewhat increased by the -additions of ground-water that SEWAGE DISPOSAL. may have filtered through the joints and brick- work of the sewers. Its chemical composition and degree of dilution varies with the charac- ter of industrial pursuits, with the amount of mineral matter naturally dissolved in the water- supply, and with the volume and rate of water- consumption. The mineral matter held in solu- tion is, as a rule, stable ; but the organic impu- rity, consisting largely of excrementitious matter, is in a state of decomposition and imparts to sewage an offensive character. In England a determination of excrementi- tious matter in sewage was as follows (vide Dr. C. Meymott Tidy) : " Every adult male person voids on an average 60 oz. ( three pints) of urine daily. The 60 oz. contains an average of 2.53 oz. of dry solid matter, consisting of Urea 512.4 grains Extractives (pigment, mucus, uric acid) 169.5 " Salts (chiefly chlorides of sodium and potas- sium) 425.0 " 1106.9 " = 2 -53 02. SEWERAGE AND SEWAGE. 9 "Every adult male person voids about 1750 grains (or 4 oz.) of faeces daily, of which 75 per cent, is moisture. The dry fecal matter passed daily is therefore about i oz. per adult head of the population. Of this dry fecal mat- ter about 88 per cent, is organic matter (of which 6 parts are nitrogen) and 12 per cent, inorganic, (of which 4 parts are phosphoric aci^l). Of this dry fecal matter n per cent, is soluble in water." Another determination for a mixed population of 10,000 inhabitants gives 22,659 ^ s f fresh urine, or 956 Ibs. of dry constituents, which is equivalent to about 36!- oz. of fresh urine and 1.53 oz. of dry constituents for each person per 24 hours; also 1775.5 ^s. of fresh faeces, or 415.8 Ibs. of dry constituents, which is equivalent to 2.84 oz. of fresh faeces and .66 oz. of dry constit- uents for each person per 24 hours. The Rivers Pollution Commission of England, in the report on the pollution of the Mersey and Ribble basins, gives the following condensed re- sults showing the average composition of sewage SEWAGE DISPOSAL. collected from thirty towns, and fairlv representa- tive : IN PARTS PER 100,000. Description. Solution. Suspended Matter. Total in Solution and Sus- pension. Total Solids. Mineral. Organic. Total. Water-closet Towns.. 72.2 24.18 20.51 44.69 116.89 The results of recent investigations in the United States with respect to the composition of sewage are perhaps succinctly condensed in the report of the Massachusetts State Board of Health of 1890, which states that : " Sewage varies much in the amount of impur- ity it carries, depending upon the amount of water used. It is much more dilute in American than in European cities. Here a sewage stronger than ordinary would contain, say, 998 parts of pure water, i part of mineral matter, and i part of animal and vegetable matter. " Sewage would become entirely purified if we should take out the 2 parts of mineral and SEWERAGE AND SEWAGE. 1 1 organic matter and leave the 998 parts of pure water ; but, as the mineral matter is not gener- ally objectionable, we are satisfied to call sewage purified if we succeed in taking out the i part of organic matter. "Of the two parts of mineral and organic matter in one thousand parts of sewage, about one half is in suspension and can be strained out by the finest strainer that water will pass through ; the other half is dissolved in water and cannot be thus strained out. " Sewage as it issues from the city sewers con- tains no dissolved oxygen and no oxidized nitro- gen. The available oxygen of the water has all been consumed in the oxidation of a portion of the carbon of the organic matter, and has not sufficed for the oxidation of the nitrogen also. In this condition it is not the repulsive fluid it is popularly supposed to be. Further and com- plete decomposition can only go on by access of an additional supply of oxygen which the sewage may take up from the air or from the water into which it flows," SEWAGE DISPOSAL. The average composition of the sewage of Lawrence, Mass., for a period of twelve months in 1888 and 1889, during which time there were made numerous analyses, is : IN PARTS PER 100,000. 1888 and 1889. Residue on Evapora- tion. Ammonia. Mean of 12 months. Loss on Ignition. Fixed. Free. Albu- minoid. Sum. Unfiltered sewage, .. . . Sewage filtered through filter-paper . . IQ.II 12.10 63 29-83 23.53 79 1.8202 I.77IO 97 .5302 .2675 50 2.3504 2.0385 87 Per cent The total solids of unfiltered sewage are here 48.94 parts per 100,000, or about -^ of i per cent. ; and they are a little less than one half the total solids in sewage as given by English analyses, namely, 116.89 parts per 100,000. Just how to remove from sewage or to ren- der innocuous this small fraction of decompos- able organic matter, seldom exceeding ^ of i per cent., is the problem that is involved in all methods of sewage disposal. Whatever may be SEWERAGE AND SEWAGE. 13 the method employed, it must be of prompt ap- plication ; for untreated or undiluted sewage will within a very few days after its discharge from sewers, and under favorable conditions of tem- perature and rest, undergo such putrefactive changes as will evolve gases of a highly offensive character, and as will render the sewage difficult of treatment. 14 SEWAGE DISPOSAL. CHAPTER II. VITAL PROCESS OF PURIFICATION. SCIENCE tells little that is satisfactory of the origin of life and matter ; of the almost sponta- neous development of the one and of the subtle processes at work in the transformation of the other. It tells us, however, that matter is inde- structible, and is composed of a few elements united in obedience to natural law into bodies of a variety of forms and conditions. Of these forms of matter, some become the embodiment of life and energy ; and others are inert and pas- sive, but contribute in some measure to the support of life. Science tells us further that there is a continual transition of matter between the vegetable and the animal forms, and between the organic and the inorganic state. Thus the active and living forms of to-day die, decay, and are resurrected in other new and living forms, just as the animal creation by its life processes, VITAL PROCESS OF PURIFICATION. I 5 its death and decomposition, supplies vegetation with sustenance ; or as vegetation, both dead and alive, contributes to the support of animal life. In many instances, at least, it is now known that organized life is the agent of these transforma- tions. Thus in the decomposition of nitroge- nous matter micro-organisms are known to be the active agents. This was indicated by the ex- periments of Schwann and Schultze in 1839, and later by Pasteur, who showed that the putrefac- tive change of organic matter was due to the vital activity of minute forms of life.* Micro-organisms are forms of life which are invisible to the naked eye, among which certain forms known as bacteria, and now regarded as belonging to the vegetable kingdom, are asserted to be the principal agents in the purification of water polluted with organic matter. So minute are these plants that the characteristics of many of them cannot be satisfactorily studied even with the most powerful microscopes ; conse- * Schloesing and Muntz in 1877 brought forward practically con- clusive proof of this. See Mass. St. Bd. of Health Report, 1890. 1 6 SEWAGE DISPOSAL. quently many of the investigations regarding their life habits which had been made by the aid of the microscope previous to the year 1881 are somewhat indefinite. In that year, however, Koch developed his method of growing these bacteria by " cultures" on gelatin plate and in other nutritive compounds, by means of which growths they began to be studied in "colonies" by the naked eye. These bacteria pervade the air, the water, the soils, and are to be found almost everywhere in nature. They are abundant in the human sys- tem. Some varieties are supposed to be the ori- gin of certain diseases. The readiness with which they may be taken into the human system by means of water and food-supplies has led to an extended study of their life habits and processes by many investigators, prominent among whom are Koch and Pasteur. To these gentlemen is assigned the chief credit of the development of the science now known as bacteriology. The application of this science to questions of sewage disposal is of much service. VITAL PROCESS OF PURIFICATION. 1 7 The organic impurity of fresh sewage, being in a state of decomposition, gives off organic vapors which are somewhat offensive. There are, however, no putrefactive changes in sewage in the condition in which it is ordinarily dis- charged from public sewers, but in it are a vast number and many varieties of bacteria, very often to the number of several hundred thousand or even a million per cubic centimetre (about a cubic f inch), and no free oxygen ; for the oxygen that the water of sewage may have con- tained previous to its pollution with organic im- purity has been consumed in chemically uniting with the carbon of this impurity, thus forming carbonic acid and free ammonia. Aside from this initial chemical reaction there is little change to be noted in sewage until after it is dispersed through a body of water or distributed over porous ground, when there begins a process of change of the nitrogenous parts of the organic matter from the state of ammonia to that of nitric acid ; which acid, in its turn, unites chemi- cally with some mineral dissolved in the sewage 1 8 SEWAGE DISPOSAL. to form a harmless inorganic compound, usually termed nitrate in a sanitary analysis. This process is termed nitrification. It is like- wise one of purification ; for it denotes a change of the nitrogen compounds, which constitute the unstable and polluting constituents of sewage, from the changeable organic condition to the stable and harmless inorganic condition, by vir- tue of their continued union with oxygen as the process of change proceeds. In its results it amounts to an oxidized or burned-up condition of the organic impurity ; but of the process it- self the active agents are certain varieties of the bacteria which infest sewage and which have the power of decomposing the nitrogen compounds in the presence of oxygen. Of this vital ac- tion of bacteria upon organic matter there is proof ; for if sewage be sterilized that is, ex- posed for a time to a temperature sufficiently high to destroy any life that may be in it there will take place no change in the nitrogen com- pounds, even in the presence of air or other source of oxygen, until seeded with sewage or VITAL PROCESS OF PURIFICATION. 1$ other decomposing matter known to contain the nitrifying organism. Likewise, antiseptics will arrest decomposition ; and the change from one condition to another of the organic impurity is practically confined to a range of temperature between 32 F. and 131 F., which range is iden- tical with that admitting of life among bacteria. Of nitrification the report of the State Board of Health of Massachusetts states that : " Oxida- tion ot organic matter, such as we have under consideration, does not go on in nature without the presence of these minute organisms, even though the supply of oxygen is unlimited. By chemical means, as in the use of oxidizing agents, such as nitric acid, potassium permanga- nate, and the like, we can break up organic matter and accomplish its partial oxidation. The effect of these oxidizing agents is, however, limited to the carbon, hydrogen, and sulphur of the organic compounds, and does not extend to the nitrogen. Ammonia is invariably formed when nitrogenous organic matter is thus treated. Except when we have the action of nascent oxygen, as in the gal- 2O SEWAGE DISPOSAL. vanic decomposition of water, we may say that the oxidation of organic nitrogen requires the presence and vital activity of bacteria." The Board of Health found nitrification to be prac- tically arrested at temperatures of sewage below 39 F. Nitrification, which is a process of nature re- quiring the presence of oxygen, produces no offence. It is analogous to fermentation and putrefaction, of which processes the former is produced by living yeast-cells, and the latter by bacteria which are supposed to be of a different variety than the nitrifying species, inasmuch as they are active in the absence of oxygen at favor- able temperatures. Thus sewage left to stand insufficiently diluted with water will putrefy and exhale sulphuretted and phosphuretted hydrogen gases. The method by which the activities of the nitrifying organisms decompose organic matter has not yet been made clear by the bacteriolo- gist ; but the observed results of these activities leave no doubt of a process of decomposition VITAL PROCESS OF PURIFICATION. 21 and purification. Several investigators have suc- ceeded in isolating a bacillus which would com- pletely nitrify ammoniacal solutions. But all bacteria in sewage do not appear to have the same functions ; for certain varieties are known to have the power of reducing nitric acid that is, the power of absorbing a portion of the oxygen of nitric acid and of thus reducing nitrates to the less oxidized condition of organic matter as represented by the nitrites, or even to ammonia as some chemists assert. In fact these distinctive and apparently opposite functional characteristics may have been potent factors in leading to the discordant and conflicting opinions as formerly expressed by independent investi- gators. Thus when the Massachusetts State Board of Health took up its investigation the following views as stated in its report were cur- rent, namely : i. ''That there is a group of bacteria capable of oxidizing ammonia to nitric acid, and another and separate group able to reduce nitrates to nitrites in the presence of organic matter. Both 22 SEWAGE DISPOSAL. kinds are widely and abundantly distributed. Attendant circumstances determine whether the reducing or the oxidizing groups will gain the upper hands." (Her&us.)* 2. "That all kinds of bacteria, under favor- able circumstances, are capable of producing nitric acid, and that the same organisms in the presence of organic matter are capable of reduc- ing nitrates." (CV//z'and Zucco. Leone.)* 3. " (a) That different species of bacteria vary greatly in their ability to reduce nitrates ; and (ft) that there is no reliable evidence that any individual species is able to oxidize ammonia either to nitric or nitrous acid." ( Warrington. Frankland^) But the results of the investigations of the Massachusetts State Board of Health showed that, while there was no doubt a nitrifying organism, it did not respond to "culture" on the gelatine plate. Concerning these organisms the report states that " they are grouped very char- acteristically in irregular clumps and are held together by a jellylike material. Each aggrega- * See Report of E. O. Jordan and Ellen H. Richards in Report Mass. State Bd. of Health, 1890. VITAL PROCESS OF PURIFICATION. 2$ tion is indeed a typical zoogloea. . . . These masses of zoogloea, obtained as a pure culture from a nitrifying solution, resemble significantly the zoogloea discharged in considerable quantities from the filter-tanks at Lawrence."* " Besides the bacteria found in the materials of which the filters are made, the microscope reveals a variable quantity of brown flakes, or flocks of amorphous matter, which appear to be largely a peculiar form of bacterial jelly, myco- derm or zoogloea. This is so constant through- out all the tanks, and apparently so characteristic, that it demands special consideration. From what has been said above it is evident that it is the only organic material, visible with the micro- scope, which occurs throughout the tanks from top to bottom. It cannot be regarded as an accidental accumulation of debris, since it is ssen- tially uniform in character and is attached to the sand-grains as if it had formed there, rather than as if it had been accidentally detained. From its * See Report of E. O. Jordan and Ellen H. Richards in Report Mass. State Bd. of Health, 1890. 24 SEWAGE DISPOSAL. connection with the sand-grains and its micro- scopical appearance there is no reason to doubt that it is, for the most part at any rate, the peculiar gelatinous condition of bacterial develop- ment known as mycoderm or zoogloea. Its abundance in the sands is remarkable, nearly every grain, in some cases, being clothed with a mantle of zoogloea. We have reason to believe that in this stage the bacteria are still alive and active though they may not grow upon our gelatine plates. We also have some indications that a sand-filter is ineffective until this zoogloea has begun to form, although it appears that a mature filter is not a mechanical purifier, but rather a respiratory mechanism. The analogy to fer- mentation by yeast, in which a large amount of chemical change is effected by a relatively small amount of yeast, naturally suggests itself, inas- much as the chemical changes effected by a mature filter are enormous and out of all obvious proportion to the discoverable changes in the zoogloea or the nitrifying organism. The anal- ogy is entirely reasonable, since fermentations VITAL PROCESS OF PURIFICATION. 2$ produced by bacteria are known to resemble closely those produced by yeast. It is also possi- ble that the zoogloea in the filters represents the nitrifying organism in a peculiar phase of its life- history." The vital process of purification when consid- ered simply as a theory is the most rational one that has ever been advanced to explain the trans- formation of organic matter in polluted water to inorganic compounds. With no other founda- tion than the analogous process, which may be observed everywhere in nature, of vegetable life absorbing from disorganized nitrogen compounds the elements of its existence, in which process water performs the interesting and important part of collecting these compounds from the air and soils and of delivering them to vegetation in a proper condition for absorption and for trans- formation into living forms, the theory, as such, is a very substantial one. But it has become more than a theory, it has become an established fact ; for the opinions derived by analogy from the observed phenomena of nature have been 26 SEWAGE DISPOSAL. substantiated and conclusive evidence has been furnished by the independent investigations of various scientists, leading to a consensus of con- clusions regarding its truth. In fact, the principles of this process are now known to possess an important bearing upon questions relating to the purity of water supplies and to successful sewage disposal, and they are coming to be generally regarded in carrying out projects for the satisfactory accomplishment of these ends. A failure to accord to them due con- sideration may result in much future trouble and annoyance. The acceptance of the vital process of purifica- tion in a measure sets aside the purely chemical theory. While it is true that chemical reactions do occur and are a part of this process, it is now held that these reactions are rendered possible only by the activities of bacteria, thus becoming secondary and dependent rather than primary factors of the process of purification. DISPOSAL BY DILUTION. 2J CHAPTER III. DISPOSAL BY DILUTION. THE disposal of sewage by dilution is simply the discharge of sewage into bodies of water sufficiently large to prevent offensive decomposi- tion. The recipient body of water naturally assumes the same relation to the outfall sewers as does the house-drain to the dwelling ; in other words, the service which the main drains of the country perform for communities in the removal of waste matter is but analogous to that which is performed by the house-drains of the sewer system for every habitation. Indeed, so natural is the transition from the artificial to the natural water-carriage system of sewerage that we find creeks and rivers used as public sewers, not only as a meas- ure of expediency and economy, but also as 28 SEWAGE DISPOSAL. though by virtue of an inalienable right and in- disputable authority inherited from nature. Should these creeks and rivers be of large volume as compared with the amount of sewage enter- ing them, of high velocity, and of continuous flow, then the disposal of sewage by water becomes so simple, so complete, and so effective that, as such, there seems to be little or nothing more to be desired. But should the receptacles of sewage be small brooks and tributaries in which the con- stant flow is but little greater than the amount of sewage entering them, then the resulting condi- tions may cause offensive odors or even nuisances during warm seasons of the year. Such outfalls must ultimately be abandoned for less objection- able ones into larger bodies of water, or the sewage must be diluted to such an extent or treated in such a manner as to prevent offence. When, however, the outfall sewers discharge into tidal rivers, the conditions affecting sewage disposal by dilution become more complex, for the sewage oscillates up and down the river with each ebb and flow of the tide, and partakes of a DISPOSAL BY DILUTION. 2$ resultant translation downward and seaward that is dependent upon the relative effects of the natural and tidal flows of the river. If these be such that the sewage is retained for some time in the tidal prism of the river, offensive putre- faction may take place. To a certain extent the period of retention may be determined by series of float observation so prolonged as to include the combined and re- sultant effects of winds, tides, and the natural flow of the river at the different seasons of the year. At the same time, other physical char- acteristics of the river affecting sewage disposal by dilution, such as temperature, specific gravity, and chemical characteristics, may be determined. But unfortunately the necessary time and means are not always available for the purpose of col- lecting by such tedious methods those data that are necessary for reaching positive conclusions in advance of the construction of a system of sewers, and it frequently becomes necessary to execute the work expeditiously and economically, and to utilize for the then present purposes the most 30 SEWAGE DISPOSAL. available points of outfall, awaiting the time when sewage, acting the part of the float in the tidal prism of the river, will demonstrate wherein lies the danger, if any, of offensive putrefaction. But realizing the advantage of anticipating an evil or unfavorable result, rather than of awaiting its coming, and having available data relating to the discharge of the river, then the rate and amount of translation may be approximately estimated, as follows : At the point of outfall determine the cross-section of the river or estuary. Compute the volume of the tidal prism above this sec- tion, having for bounding surfaces the areas re- spectively of overflow at mean high tide and at mean low tide, and an altitude equal to the mean tidal rise or fall ; a quantity of water equalling the volume of this prism, and that of the natural flow of the river (usually at a low stage) must discharge through the section of measurement during the time of ebb tide, and must spread out in a reach of the river below. Now the distance which sewage would be carried up stream by a flood tide would depend upon the relative portions of the DISPOSAL BY DILUTION. 31 tidal prism which would be filled by the up-stream flow of the tide and the natural flow of the river, assuming the tidal flow to act piston-like upon the flow of the river. This method assumes that the velocity of flow through the cross-section is uni- form, that there is no dispersion of the sewage and no wind effects, conditions which in nature do not obtain, consequently the method is but a crude substitute for the more reliable ones of di- rect observation. However, by whatever method the effects of a sewage disposal into tide-water may be determined, whether by the actual ex- perience with sewage discharged at convenient points, or by the more rational method of collect- ing and analyzing those data that may relate to such a disposal of sewage, and of drawing conclu- sions therefrom, it follows that, if offence become assured as a result of a certain line of practice, or if it be anticipated as a result of a close and careful investigation, a future disposal must contemplate works to remove the sewage to more remote points, where no ill effects will result. Such works may consist of long lines of intercepting 32 SEWAGE DISPOSAL. and outfall sewers leading to some distant locality where the sewage can be safely thrown into water or upon land ; or of a plant for purifying the sewage before discharging it either into water or upon land. Their precise character, however, will de- pend upon local requirements and natural facili- ties, in whatever way that they may affect the questions at issue. Having briefly alluded to the several condi- tions under which sewage disposal by water is met with in practice, it will be interesting to consider the amount of dilution that may be necessary to prevent offensive putrefaction of sewage, and the processes of nature that result in the purification of sewage-polluted water. The amount of sewage that may be committed to a body of water without fear of offence is de- pendent upon the balance which may exist be- tween the natural processes of decomposition and of purification, as they may be active in the polluted water. Should the products of decom- position of the organic impurity exceed an amount that can be naturally absorbed by the DISPOSAL BY DILUTION. 33 diluting water, the exhalation of offensive gases will ensue. On the other hand, if these products be all absorbed no offence will follow, although the water may be somewhat unsightly. It is not easy, however, to determine just what the relation by volume of the sewage to the dilutent should be for there is not available a sufficient amount of experimental data and ob- servations upon the subject to admit of a positive conclusion. Moreover, that relation which might answer in one locality would not necessarily apply in another, for the dissolved and suspended constituents of natural waters in a normal condi- tion, their average temperature and their organ- ized life, are all subject, more or less, to seasonal and geographical variations, which variations, as associated with other physical properties of natural waters, will qualify its natural purifying power. Such observations as have been made in different localities enable us to form certain estimates and deductions as to what this relation should be. The State Board of Health of Massachusetts, which through its eminent scientists and engineers 34 SEWAGE DISPOSAL. has given considerable attention to the study of the water supplies of Massachusetts, has sug- gested, as a result of experiment and observation, that, in a river continuously flowing at a sufficient velocity to prevent deposits, there should be a discharge of 2.5 to 7 cubic feet per second for every one thousand inhabitants, which is equiva- lent to a dilution from 1 6 to 45 times the volume of sewage, assuming the rate of water consump- tion per capita to be 100 gallons per day, and that the amount of water consumption is a meas- ure of the volume of domestic sewage. It was recommended for Chicago by the Drainage and Water-supply Commission that pro- vision be made in the discharging capacity of the new drainage canal, now under construction, for a dilution of sewage with water from Lake Michigan to the amount of four cubic feet .per second per one thousand inhabitants, which is equivalent to a dilution of about 26 times the volume of the sewage, assuming the daily rate of water consumption to be i oo gallons per capita. By daily pumping 440,220,867 U. S. gallons of pure DISPOSAL BY DILUTION. 35 cool water from Lake Michigan into the navigable outlet basin of the Milwaukee River at a point about 3 \ miles from the harbor entrance, this basin, which receives daily about 13,000,000 gallons of sewage from a large district of the city of Mil- waukee, is so completely flushed and the sewage so thoroughly diluted as to effectually abate the intolerable nuisance of putrefying sewage that had for years annoyed the inhabitants of that city. In this instance a dilution of about 34 times the volume of sewage prevents offence ; but it is esti- mated, as the result of experiments made upon a small scale, that a dilution of 25 to 30 times the volume of sewage would be equally effective.* But degrees of dilutions somewhat less than those just stated have been found to give offence. Thus the sewage of the city of Chicago as it flows from the Bridgeport pumping-station through the Illinois and Michigan Canal, diluted with four times its volume of water from Lake Michigan, has given offence at Joliet, 33 miles below the point * See article by G. II. Benzenberg, C.E., in Trans. Am. Soc. C. E., Nov. 1893. 36 SEWAGE DISPOSAL. of its discharge into the canal. The Blackstone River of Massachusetts, receiving the sewage of Worcester and diluting it by a continuous dis- charge of 1.77 cubic feet of water per second for the sewage of each one thousand inhabitants, is very offensive immediately below the city ; but at Uxbridge, 16 miles below, the discharge of the river for each one thousand inhabitants is 3.88 cubic feet per second and gives with this degree of dilution no offence to dwellers along the river.* It is, therefore, quite clearly indicated that a proper disposal of sewage into a river continu- ously flowing with a sufficient velocity to prevent deposits should be restricted to that amount of sewage which the river can absorb and purify without offence at a stage of minimum flow. And usually it may be well to observe the same relation between the volumes of sewage and diluting water, even when the natural flow of a river becomes opposed by tidal currents ; for the ebb and flow of the tide affects the natural flow of the river very much as would a dam periodic- * Report Mass. State Bd. of Health, 1890. DISPOSAL BY DILUTION. 37 ally lowered across the river and as often raised therefrom, inasmuch as such a damming back of the water simply change the conditions of flow without affecting the actual amount of water that is discharged into the sea. It is particularly necessary to observe proper proportions of sewage dilution and a favorable temperature of the diluting water when the discharge of sewage is into harbor basins or estuaries ; for there various conditions combine to produce serious pollution. These conditions and their effects will appear in a more striking light when illustrated by practical examples. The city of Milwaukee discharges a large por- tion of its sewage into the Milwaukee River. This river drains a watershed of about 675 square miles ; but, notwithstanding so large a drainage area, its average summer flow is not over 15,000,- ooo gallons per day, and at exceedingly dry times it ceases altogether. It discharges into Lake Michigan through a long basin that has been artificially made navigable for lake craft for a distance of 'about 2\ miles from the harbor 3$ SEWAGE DISPOSAL. entrance. The current through this basin is naturally exceedingly sluggish during the ordi- nary summer flow, and is subject to the effects of winds upon the lake.* The amount of sewage daily discharged into this basin is, as has been stated, about 13,000,000 gallons. The velocity of natural flow through this basin being insufficient to carry into the lake the insoluble portion of sewage, it deposits upon the bottom of the basin and in the slips as a semi-fluid sludge, which, during the summer when the temperature of the water in the basin becomes 70 F. or more, putrefies and exhales unwholesome and offensive gases. To obviate the annual summer-stench nuisance, there was constructed a conduit 12 feet in diameter and 2500 feet long from the lake to a point in the river about 3^ miles above the harbor entrance, where there is a dam. Through this conduit a volume of water equal at least to 25 times the volume of the daily flow of sewage, is daily pumped from the lake into the river during a * G. H. Benzenberg, Trans. Am. Soc. C. E., Nov. 1893. DISPOSAL BY DILUTION. 39 considerable portion of each year, thus effecting a thorough dilution of the sewage, a cessation of putrefaction, a removal of all discoloration from the river water, and a complete abatement of the stench nuisance. Likewise the city of Chicago has for years discharged 85 per cent, of its sewage into the Chicago River. This river drains a flat territory of about 130 square miles lying between Lake Michigan and the Des Plaines River, and dis- charges into Lake Michigan at a point very nearly in the east-central portion of the city. For a distance of i mile from its mouth and for 6 miles or more along both the north and the south branch, this river has been artificially formed into a navigable basin of 10 to 15 feet in depth and of an average width of 150 feet ; in which basin at times of summer flow there is no perceptible natural current. On the South Branch is located the Bridgeport pumping plant, which lifts the sewage from the river, diluted as it is at this point with four times its volume of lake water, and discharges it into the 40 SEWAGE DISPOSAL. Illinois and Michigan Canal, thereby reversing the natural direction of. flow and drawing water into the river channel from the lake. At times of overflow from the Des Plaines River nearly all flood-water passes through the Ogden-Wentworth Ditch into the South Branch, thence through this branch into the lake. For years, the insufficient dilution, high temperature of the river water, and masses of putrefying deposits of organic matter had caused intolerable nuisances at many points along the river. The production of these offences has lately been somewhat impeded by pumping the sewage and by flushing the river channel with lake water ; but eventually when the new drain- age canal, now under construction, is completed, which is intended to remove the entire sewage of Chicago diluted with about 26 times its volume of lake water to the Illinois River, these offences will be completely removed and the river water rendered clear, cool, and unobjectionable.* The sewage of the city of London is dis- * See Reports Chicago Drainage and Water-supply Commission. DISPOSAL BY DILUTION. 4! charged into the Thames at the mouth of Bark- ing Creek, about 30 miles or more from the open sea. The average natural flow of this river is about 1,620,000,000 U. S. gallons per day, while that of the driest years is about 1,080,000,000 U. S. gallons per day. The water consumption of London for a population of 5,237,000 is about 205,500,000 U. S. gallons per day, of which amount about 156,000,000 U. S. gallons per day is taken from the Thames. The available dilu- tion of the sewage by the average natural flow of the river, as measured by the volume of water consumption, amounts to about nine to six times the volume of the sewage. Now the sewage which is discharged into the Thames has been estimated to remain in the tidal prism of the river, from twelve days during heavy floods to thirty-three days during dry-weather flow ; con- sequently, with the under-dilution which the sewage receives, it is very likely to putrefy. In fact, in the year 1884 the Royal Commission on Metropolitan Sewage Discharge reported " that during hot and dry weather there is serious nui- 42 SEWAGE DISPOSAL. sance and inconvenience extending to a consider- able distance both below and above the outfall, from the foul state of the water consequent on the sewage discharge. The smell is very offensive and the water is at times unusable." This Com- mission, assuming that the chief cause of the offences which it had observed in the river Thames lay in the putrefaction of the insoluble portions of the sewage, which were either depos- ited or were wafted to and fro by the tide, rec- ommended the removal of these insoluble matters from the sewage previous to discharging it into the river. Several cities of this country which discharge sewage into estuaries at points a long way re- moved from the open sea, and which have had experiences similar to London, are adopting a similar method of sewage treatment, but with what degree of success is not yet apparent. On the other hand, the cities of New York, Brook- lyn, and Jersey City, which discharge sewage into the Hudson and East rivers, tidal estuaries, have as yet experienced, as a result of this prac- DISPOSAL BY DILUTION. 43 tice, no serious offence, because there is an ample dilution, a sufficiently low temperature of the water, and the requisite rapidity of dispersion to prevent nuisances. But to refer again to the cities of Chicago and Milwaukee, it is well-known that the temporizing methods of sewage disposal as long practised in these two cities had led to very grave and serious offences, and as a result may have caused impressions quite prejudicial to sewage disposal by dilution. But, as a matter of fact, until the introduction of the present methods of flushing the river by pumping into it large volumes of water from Lake Michigan, these cities neither disposed of their sewage nor diluted it, but turned it into a sluggish basin, as into a cesspool, to deposit sludge and to putrefy, until floods in the rivers should remove the deposits of sludge and carry it into the lake, or until cool weather should arrest putrefactive decomposition. In these practices the principles of natural in- offensive purification were wholly ignored ; and not until the results of temporizing expedients 44 SEWAGE DISPOSAL. became no longer endurable were the facilities and means supplied by the communities with which to correct the evils. But this phase of the subject cannot be here passed over without a brief reference to the bear- ing which the physical characteristics of water have upon sewage disposal by dilution. When sewage is discharged into quiet or slowly-moving bodies of water, the greater part of the insoluble portion of it eventually deposits, the heavier particles falling near the sewer outfall and the lighter ones becoming more widely distributed. From these decomposing deposits gases may emanate. If they exceed an amount which the diluting water can absorb, that is, if they produce over-saturation in the water, they will bubble through into the atmosphere. The rapidity with which these gases can be formed will depend very much upon the temperature of the water surrounding the deposits from which they arise, a high temperature promoting rapid decomposi- tion. It was noted in the Milwaukee River that at temperatures below 69 and 71 F. there was no DISPOSAL BY DILUTION. 45 visible exhalation of gases, but that at higher temperatures they bubbled forth profusely. Simi- lar phenomena can be noticed in any sluggish stream receiving more sewage than it can suffi- ciently dilute, or in any shallow pond containing deposits of organic matter ; for the gases bubble out much more freely at summer than at winter temperatures. These observations indicate that the diluting water should be as free as possible from organic impurity in order that it may absorb and oxidize the gases from decomposing sewage ; that its temperature should be sufficiently low to prevent or arrest putrefaction ; and that it should have a sufficient movement of translation to give the requisite amount of dilution. The conditions affecting the disposal of sewage when 'sewage is discharged into the open sea, bays, lakes, ponds, or into similar non-flowing bodies of water are quite different from those in flowing rivers, although the process of purification of organic impurity of sewage is precisely the same in either instance. 46 SEWAGE DISPOSAL. Here the only natural means of removing and distributing the sewage are the inconstant and fluctuating tidal and wind currents. It is, there- fore, necessary that proper dilution be attained by a dispersion of the sewage through the body of water into which it is discharged. The method by which such dispersion can be effected will depend very largely upon the local conditions. Even the rate of dispersion will depend to a considerable extent upon the relative physical condition of the sewage and the diluting water, and upon the manner in which the fluids are brought in contact. Should the weight per unit of volume and the temperature of each be identi- cal, there would be a rapid intermingling of the particles of the one with those of the other. But should the sewage be at a higher temperature than that of the receiving water it would tend to rise and distribute over the surface of the water, if discharged beneath it ; or should the sewage be colder than the receiving water, it would tend to displace it. Thus in one instance dis- DISPOSAL BY DILUTION. 47 persion would be accelerated and in the other retarded. In a similar manner a difference in the weight per unit of volume of the two liquids at the same temperature would affect the rate of dis- persion, as when sewage is discharged into salt water. One is not impressed regarding the sensitive- ness of water of different densities to temporarily stratify, as it were, on being brought into con- tact, until having made the experiment; neither does this physical characteristic seem of much practical importance ; but it is the advantage that is taken of just such principles of nature as is here involved that affords the economical and suc- cessful solution of many engineering problems. In 1889 the State Board of Health of Massa- chusetts made some observations on the dis- charge of the sewage of Boston into the sea at Moon Island, and states that "at Moon Island, the outlet of the Boston Main Drainage System, the sewage collected in eleven hours is generally dis- charged in a body in about half an hour, and no 48 SEWAGE DISPOSAL. sewage is to be found in the tidal current into which it enters two hours after it leaves the sewer." As one of the experiments of that Board of Health, sewage was discharged for four hours on a falling tide at the rate of 1,500,000 gallons per hour. When sailing in the stream of sewage, on its leeward side, the odor was found to be disagreeable for a distance of one half-mile from the outlet, but at a distance of three-quar- ters of a mile from the outlet no odor could be detected. The flow of sewage could be followed by the eye, by means of the comparative stillness and browner color of the sewage, to a point one mile from the outlet. At one and one-quarter miles distant sewage effect was scarcely discern- ible, and at one and one-half miles no trace of sewage was visible, although floats which started with the sewage had gone far beyond this limit. Chemical analyses of the sea-water, made at the same time, fully substantiate the physical ob- servations and are as follows (expressed in parts per 100,000) : DISPOSAL BY DILUTION. 49 Free Ammonia. Albumi- noid Ammonia. Sum of Ammo- nias. Chlorine. Salt water, up stream from area containing sewage . . . 00^6 0098 Ol ZA I 67^ Salt water, down stream from area containing sewage 0056 OOQ^ 01 51 I 746 Water within area containing sewage at the following dis- tances from outlet : 400 feet . 2 5OO c q jo