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 
 
 <j o^I 
 
 773 
 
 i 600 
 
 IQ44 
 
 06^6 
 
 2580 
 
 I ^70 
 
 2OO 
 
 O4l6 
 
 .02=54. 
 
 OO7O 
 
 I 621 
 
 4 700 
 
 .O224 
 
 .OIl6 
 
 .0^40 
 
 I,6Q4 
 
 6 200 . ... 
 
 Ol84 
 
 0156 
 
 O^4 
 
 I 689 
 
 7 200 
 
 0136 
 
 oioS 
 
 O244 
 
 I 68? 
 
 Q 2OO 
 
 .OIO4 
 
 .OOQ6 
 
 .O2OO 
 
 I ^IO 
 
 Water in mid-stream at cross- 
 ing of North Ferry to East 
 
 O48O 
 
 OIC4 
 
 .06^4 
 
 i f;8i 
 
 
 
 
 
 
 11 From these analyses it appears that in the 
 stream of sewage at 400 feet from the 
 outlet of the sewer the upper eight inches in 
 depth was about one-half sewage. At 1600 feet 
 distant it contained about one-eighteenth of 
 its bulk of sewage, and at 3200 feet, five-eighths 
 of a mile distant from the outlet of the sewer, the 
 ammonias indicated the amount of sewage added 
 to be but one per cent, of the volume of the 
 
5O SEWAGE DISPOSAL. 
 
 water, and the same amount as found in mid- 
 stream at the crossing of North Ferry to East 
 Boston. Beyond this distance the amount of 
 ammonia added became one-half of one per cent, 
 at a mile, and less than one-tenth of one per 
 cent, at one and four-fifths miles from the outlet." 
 This report further states that " the dis- 
 charge of sewage from the reservoir at Moon 
 Island is begun either one or one and a half 
 hours after high tide, when the outward current 
 past the outlet is well established. About 
 15,000,000 gallons of sewage are discharged in 
 about forty minutes. As the sewage is lighter 
 than the sea-water, it rises towards the surface 
 soon after being discharged and spreads out until it 
 has a depth of less than a foot. Half an hour from 
 the beginning of the discharge the sewage covers 
 an area about half a mile in diameter. In this 
 condition the sewage, already considerably diluted, 
 moves outward with the current and further dilu- 
 tion takes place, the process going on most rapidly 
 at the bottom of the layer of sewage. Up to a cer- 
 tain stage in the progress of this dilution, the sur- 
 
DISPOSAL BY DILUTION. 51 
 
 face of the sewage contains enough greasy matter 
 to prevent waves, except when the wind blows very 
 hard. When the dilution of the sewage has pro- 
 gressed so far that waves begin to form and its 
 specific gravity has approached that of the sea- 
 water, it rapidly becomes mixed with water from 
 greater depths, and very soon cannot be distin- 
 guished by the eye or nose from unpolluted sea- 
 water. The last change here described usually 
 takes place in less than an hour and a half after 
 the sewage is discharged, and at a distance from 
 the outlets not exceeding two miles." 
 
 " On one occasion bottles were filled every 
 fifteen minutes from the area of sewage going 
 outward with the current. These bottles were 
 kept in an office for a long time, and those taken 
 one hour or more after the beginning of the dis- 
 charge never showed by their appearance or 
 odor that they contained any sewage." 
 
 The sewage from the Boston disposal works 
 is daily discharged into the open sea after but a 
 few hours' detention in storage reservoirs on 
 Moon Island, and is not, therefore, in a state of 
 
52 SEWAGE DISPOSAL 
 
 putrefaction. Under such conditions it is evi- 
 dent that sewage may be completely and rapidly 
 dispersed over an extended area and through a 
 large body of water in a state of agitation by winds 
 and tides, if it be unrestricted in the expanse of 
 its movement and if the time and manner of dis- 
 charge be judiciously regulated. 
 
 Somewhat different is the disposal of sewage in 
 inland lakes, for then there are no tidal currents 
 to be advantageously utilized in bearing away 
 the sewage. In Chicago, previous to the intro- 
 duction of the pumping and flushing system, 
 sewage would be detained in the river basin for a 
 week or more in a state of active putrefaction, to 
 be suddenly flushed into the lake by the flood- 
 waters of the Des Plaines River or of the North 
 Branch. So great an accumulation of putrid 
 matter must necessarily become discernible in a 
 very large volume of lake water when suddenly 
 discharged from a swollen river, yet it will be- 
 come so dispersed and diluted as to arrest putre- 
 faction, and as not to affect to any noticeable 
 extent the sanitary conditions of Chicago except 
 
DISPOSAL BY DILUTION. 53 
 
 through an occasionally contaminated water 
 supply. At Milwaukee, because of littoral cur- 
 rents, the polluted water from the Milwaukee 
 River or the sewage from the pumping-station 
 had been discernible by means of a discoloration 
 of the lake water for a distance of six miles, but 
 since the flushing system has been in operation 
 the river discharges can scarcely be detected from 
 the lake water. 
 
 Wave action in itself will give a very wide 
 dispersion of sewage and will prevent deposits of 
 insoluble matter in considerable depths of water. 
 Consequently, to avoid the danger of contami- 
 nated water supplies, the intakes of water-works 
 should be widely separated from the sewer outfalls. 
 
 Nature affords us much evidence regarding 
 the natural purification of polluted waters. This 
 natural process, particularly as it applies to the 
 purification of sewage-polluted waters, has been 
 much discussed, seriously doubted by some investi- 
 gators, and emphatically denied by others. These 
 adverse opinions have been based largely upon 
 evidence furnished by the results of the chemical 
 
54 SEWAGE DISPOSAL. 
 
 analyses of water, and have been formulated upon 
 the assumption that all progressive changes among 
 the organic constituents of water are due entirely 
 to a purely chemical action caused by the variable 
 affinities of oxygen for the elements composing 
 the several organic compounds. But as investi- 
 gations concerning these changes in water have 
 proceeded, they have gradually developed the 
 fact that chemical action between the nitrog- 
 enous constituents, at least, of dissolved organic 
 impurity and oxygen is rendered possible only 
 by the action of living micro-organisms, and that 
 without these micro-organisms there can be no 
 chemical oxidation. Furthermore, these investi- 
 gations have shown that opinions and judgments 
 regarding the character of a water, based solely 
 upon the evidence furnished by chemical analyses, 
 may be erroneous, for the dissimilar activities of 
 the so-called nitrifying and reducing bacteria 
 may cause such discordant fluctuations of the 
 nitrogenous compounds between the organic and 
 inorganic state in which they may be found in 
 water that the results of chemical analyses alone 
 
DISPOSAL BY DILUTION. 55 
 
 may afford no true evidence regarding the pro- 
 gressive changes touching the purification of 
 water. To make this still clearer, chemists have 
 asserted that nitric acid, the completely-oxidized 
 condition of nitrogenous matter, may be reduced 
 in the presence of organic matter both to nitrites 
 and free ammonia ; but these two nitrogen com- 
 pounds represent, as usually interpreted in a sani- 
 tary analysis, certain intermediate stages in the 
 process of nitrification of organic matter in pol- 
 luted water ; consequently it would appear as 
 though the mere determination of these inter- 
 mediate conditions of the nitrogenous matter 
 might be misleading evidence regarding progres- 
 sive purification to an extent proportional to the 
 reduction of nitrates. 
 
 That living organisms are primarily the cause 
 of the decomposition and oxidation of organic 
 impurity dissolved in water is certainly in ac- 
 cord with some of the observed processes of 
 nature. In support of this theory it has been 
 frequently observed that the water of a sewage- 
 polluted river progressively improves as it departs 
 
56 SEWAGE DISPOSAL. 
 
 from the point of pollution to an extent that is 
 not altogether accounted for by the additional dilu- 
 tion that the sewage receives as the result of the 
 natural accumulations to the volume of flow of a 
 river, and that the number of the bacteria con- 
 tained in this water diminish with the decrease 
 in the organic impurity. Nearly every lake or 
 pond receives many impurities from its water- 
 shed, and yet it does not show cumulative stores 
 of impurities, nor does it become permanently of- 
 fensive nor dangerously polluted. In fact, it has 
 been demonstrated that a water known to have 
 been polluted by sewage may be organically im- 
 proved by storage in reservoirs and by circulation 
 through the pipes of a water-supply system. 
 If this be generally true of sewage-polluted sur- 
 face waters artificially stored and circulated for a 
 limited time, it should be at least equally true 
 of the same waters in their normal condition in 
 nature. 
 
 It must be, therefore, that in the associated 
 presence of unstable organic matter and organ- 
 ized life, and in their common disappearence, 
 
DISPOSAL BY DILUTION. 57 
 
 there is illustrated the balance in nature of the 
 law of supply and demand by which an overpro- 
 duction in one direction is prevented by con- 
 sumption and death in another. 
 
 The teachings of nature alone are sufficiently 
 conclusive to establish the progressive improve- 
 ment and the purification of polluted normal 
 waters. 
 
 It has already been stated that the work of the 
 organisms in purifying polluted water depends 
 upon having available a supply of oxygen. Now 
 it is known that in water the available supply 
 of oxygen is greatly distributed, for water be- 
 comes saturated when it has dissolved about 3 to 
 4 per cent, of its volume of oxygen; therefore, 
 if sewage turned into a body of water be more 
 than sufficient to absorb all the dissolved oxygen 
 in the water in the process of purification or be 
 insufficiently dispersed, the changes will become, 
 to a certain extent, putrefactive, and will result 
 in the exhalation of offensive gases. 
 
 The offence of these gases and of the organic 
 vapors of sewage consists in the bad odors which 
 
58 SEWAGE DISPOSAL. 
 
 they may impart to the atmosphere, rather than 
 to any specific poisonous and disease-producing 
 properties that they may possess in the highly- 
 diluted condition in which they are inhaled. 
 When inhaled continuously, however, physicians 
 ascribe to them a depressing and enervating 
 effect upon the system which renders the person 
 less fortified against disease. 
 
 There is no conclusive evidence to show that 
 offensive putrefaction in a highly polluted water 
 exposed to the open air has been the direct 
 source of disease, for the fresh air dilutes the ex- 
 haled gases sufficiently to render them innocuous. 
 
 The bad odors themselves are no criterion of the 
 depleting effects of the gases upon the oxygen of 
 the atmosphere; for they may become an intol- 
 erable nuisance long before the life-supporting 
 properties of the atmosphere are prejudically af- 
 fected by them. 
 
 Therefore, to prevent offence to the aesthetic 
 taste and to render the air about sewage-polluted 
 bodies of water wholesome, it is necessary to ob- 
 serve the bounds which nature has placed upon 
 
DISPOSAL BY DILUTION. 59 
 
 the natural purifying powers of normal waters, 
 and not to transgress them by committing to a 
 water more decomposing matter than it can 
 purify. In other words, let the dilution be 
 sufficient to insure both the absorption of all 
 the gases of decomposition and a proper supply 
 of oxygen, then nature will see to the results. 
 
 It is now quite generally admitted that some 
 diseases may be readily communicated to the 
 human system through drinking-waters. This 
 admission is based upon the connection supposed 
 to exist between some specific living organism 
 and certain diseases, more particularly cholera and 
 typhoid fever. The evidence indicating the 
 danger of infection from this source has been by 
 some asserted to be sufficiently strong to warrant 
 the prohibition of further disposal of sewage by 
 discharging it into bodies of water. But from a 
 standpoint that fully comprehends all the ele- 
 ments involved in the question, can this position 
 be sustained ? 
 
 It is known by the evidence submitted that 
 very many of the natural waters have received 
 
60 SEWAGE DISPOSAL. 
 
 the excrement of persons afflicted with disease, and 
 presumably have thereby become infected with 
 disease-producing germs; but there is nothing 
 among the results of bacteriological research to 
 indicate, at least in this country, any progres- 
 sive increase of these germs in water after it is 
 thus infected. But, on the other hand, they in- 
 dicate that the germs rapidly disappear. Certain 
 it is that the natural environments in water are 
 unfavorable to the life of these germs, otherwise 
 it would be difficult to conceive of a water once in- 
 fected becoming again wholesome. Nature seems 
 to have set limits beyond which these organisms 
 cannot go. Whether it is the physical conditions 
 of the water or the living organisms that thrive 
 and abound therein that are most inimical to the 
 life of the disease-germs, does not seem to 
 be clearly established. However, it is generally 
 admitted that the hardier, stronger, and more 
 active water bacteria are thoroughly antagonistic 
 to the disease-producing variety, and that the one 
 speedily destroys the other. 
 
 In line with this view are the investigations of 
 
DISPOSAL BY DILUTION. 6 1 
 
 the Massachusetts State Board of Health, which 
 indicate that in the Merrimack River water, such 
 as is used for the water supply of Lawrence, 
 typhoid-fever germs live in rapidly-decreasing 
 numbers for a period of 12 to 15 days. The 
 duration of life and rate of decrease of the typhoid 
 germs seemed to be less in the natural river water 
 than in the filtered water. The longest duration 
 of life observed was 31 days. 
 
 The Report of the Royal Commission on 
 London Water Supply, dated Sept. 8, 1893, 
 says that " it appears to be the belief of bac- 
 teriologists that such [typhoid] dejecta begin 
 to lose their virulence after a very few days, and 
 the longest period for which the typhoid bacillus 
 has as yet been found to retain its vitality when in 
 fecal matter does not exceed 15 days." 
 
 On the whole, the results of investigation 
 appear to substantiate the observations and 
 teachings in nature that disease-germs do not 
 thrive in normal waters. 
 
 If, then, the conditions in normal waters be so 
 unfavorable to their vitality, and if the harmless 
 
62 SEWAGE DISPOSAL. 
 
 variety of water bacteria destroy them, it is but a 
 fair inference that such disease-germs as may find 
 entrance to sewage from human habitations and 
 other sources can find neither congenial environ- 
 ments nor long life among the multitudes of 
 vigorous bacteria of the harmless kind that are 
 known to infest sewage. But assuming that some 
 may survive and may reach the sewer outfall and 
 may live in the waters receiving the sewage for 
 certain periods of time, possessed of their vitality 
 and- infectious powers, is the position of strict 
 prohibition of sewage disposal into water even 
 then wholly tenable? The sanitary view of the 
 situation, namely, that any custom or practice 
 which tends to jeopardize the health of a com- 
 munity should be abandoned, is worthy of all con- 
 sideration. But there is a practical and popular 
 aspect of the question which will influence and 
 control innovations in established customs and 
 practices even more than will the scientific aspect, 
 and which demands experimental proof, not only 
 of the necessities for change but also of the prac- 
 
DISPOSAL BY DILUTION. 63 
 
 tical utility of sewage disposal by other and more 
 scientific methods. 
 
 It is exceedingly difficult to adduce both experi- 
 mental evidence and practical proof of infection 
 in any special instance by sewage-polluted water 
 in an amount and in a manner that is thoroughly 
 convincing. However, it must be admitted that 
 the general drift of the statistical evidence thus 
 far collected is to the effect that the cities which 
 use as a public water supply an unfiltered 
 water containing sewage impurities have a higher 
 death-rate from typhoid fever than do other cities 
 using either unpolluted water or sewage-pol- 
 luted water that has been filtered before use. But 
 this shows, as will be seen more clearly further 
 on, rather that cities and towns should use more 
 circumspection and care in the development, 
 treatment, and distribution of public water sup- 
 plies than it does that they should prohibit sewage 
 disposal by water. 
 
 Furthermore, would the abandonment of sys- 
 tematic sewage disposal into water afford im- 
 munity from infection ? As an illustration of this 
 
64 SEWAGE DISPOSAL. 
 
 point, let it be assumed that a city discharges 
 sewage from a combined system of sewers into a 
 river from which, at points below, water is ab- 
 stracted for public supplies. If this city be 
 obliged to abandon the practice of discharging 
 crude sewage directly into the river and be, there- 
 fore, required to previously treat it, it would con- 
 struct disposal works of a capacity to treat the 
 daily flow of domestic and industrial sewage, and 
 would allow the storm-water to flow directly into 
 the river because of the impracticability of hand- 
 ling and treating it at disposal works. The 
 storm-water, as it flows through such a system of 
 sewers, would become more or less polluted by 
 sewage ; and it might, consequently, carry in- 
 fection directly into the river. But even assum- 
 ing that the city be sewered by the separate sys- 
 tem of sewers, there yet remains the danger of 
 infection from polluting matter which abounds 
 more or less in the midst of every thickly-settled 
 community, and which may be washed into the 
 river by any and every storm. This illustration 
 truly depicts the condition of many cities in this 
 
DISPOSAL BY DILUTION. 65 
 
 and other countries as regards sewerage and 
 sewage disposal. 
 
 Then, again, from ships, steamboats, and other 
 craft plying a navigable river there may fall 
 fresh excrement containing disease-germs, which, 
 because of their direct contact with the river, may 
 be even more infectious than though they had 
 entered the river through a system of sewers. 
 Also from squatters' shanties, from houses which 
 are not connected with any sewer though in the 
 city, from the abodes of people living along the 
 banks of a river and beyond municipal regulations, 
 infectious matter of various kinds may reach the 
 water, In fact, there is evidence to show that 
 infection of a water may occur quite as readily 
 through isolated and uncontrollable sources as 
 through the sewers themselves. 
 
 It is, therefore, evident that as a practical 
 problem the prohibition of sewage disposal by 
 water will not and cannot prevent infection of 
 streams, rivers, lakes, and other large natural 
 bodies of water ; consequently, as a reliable 
 sanitary measure, prohibition must fail. 
 
66 SEWAGE DISPOSAL. 
 
 But this conclusion now exacts proof, either 
 of the wholesomeness of waters that are available 
 as public water supplies, even though they may 
 have been polluted by sewage at some point 
 more or less remote, or of some practical method 
 of purifying water, so polluted, previous to use 
 for domestic purposes. A thorough discussion 
 of these points would require a complete review 
 of what is known of methods of water purifica- 
 tion ; but as this is beyond the scope proposed 
 for this discussion, the author hopes to present 
 conclusive proof of these questions by illustra- 
 tion and by reference to the results of existing 
 practices. 
 
 To illustrate one element of the question, let 
 us refer to the analogy between air and water. 
 We inhale the same atmosphere that receives the 
 exhalations from healthy and diseased persons 
 and animals in open and in confined places ; from 
 the public sewers and house-drains ; from the 
 many industrial establishments which turn into 
 the atmosphere offensive, disagreeable and poi- 
 sonous gases ; and from various sources of putre- 
 
DISPOSAL BY DILUTION. 6? 
 
 faction that abound more or less in the vicinity 
 of every town ; and we do not hesitate to con- 
 fine many patients suffering from various causes 
 in the same hospital ; yet dependence in every 
 instance to prevent evil results rests largely upon 
 the diluting and oxidizing properties of the at- 
 mosphere. 
 
 In a similar manner water containing free 
 oxygen (as do all unpolluted surface-waters) is 
 a natural purifying agent for any organic pollut- 
 ing matter that may enter it. The air, it is true, 
 can destroy and render innocuous impurities 
 much more readily than can water, because of 
 the greater mobility and diffusing properties of 
 gases than of liquids ; but we have no conclusive 
 evidence in nature to show that purification in 
 the end is any more completely accomplished by 
 the air than by the water. 
 
 As the purifying power of air depends largely 
 upon circulation, temperature, and dryness, so 
 does the like property of water depend upon the 
 varying physical conditions peculiar to itself. 
 There is no arbitrary standard or formulated 
 
68 SEWAGE DISPOSAL. 
 
 method by which the scope of these powers can 
 be calculated, as this is a question to be deter- 
 mined in specific cases by special investigation. 
 Thus, in the case of pollution either of air or of 
 water, security from evil results depends largely 
 upon the dilution and the complete oxidation of 
 the contained impurities becoming, therefore, 
 an element of time and distance. 
 
 Arguments have already been advanced denot- 
 ing a progressive process of purification of natural 
 waters by dilution and oxidation of organic im- 
 purity. When this process has rendered organic 
 impurity, as such, no longer recognizable, or has 
 so far removed it that the remnant is of no prac- 
 tical importance, then the water is considered 
 wholesome from a chemical standpoint. 
 
 In line with this view, various cities take their 
 water supplies from the same rivers into which 
 sewage is discharged, and furnish the water di- 
 rectly to consumers without further purification 
 than perhaps some settlement in basins. In 
 many instances no unhealthful effects seem to 
 result from this practice, especially when the 
 
DISPOSAL BY DILUTION. 69 
 
 nearest point of sewage pollution is quite remote 
 from the intake of a water supply. 
 
 But the results of chemical analyses are alone 
 not a true index of the potability of a water ; for, 
 as has been previously shown, disease-germs, 
 which are not discernible by chemical analysis, 
 preserving their vitality for a time, may introduce 
 into water intended for domestic uses an element 
 of danger, even though the water may be chem- 
 ically recognized as wholesome. Consequently, 
 when the interval of time or distance relative to 
 the points of pollution and intake of a water sup- 
 ply is not sufficient to insure the wholesomeness 
 of a water, it becomes obligatory, with due regard 
 for the health of a community using such a 
 water, either to provide a new and uncontami- 
 nated supply or to prevent pollution of the water 
 or to purify the polluted water before use. 
 
 The choice between an old and a new water 
 is a matter of local consideration. 
 
 To prevent the pollution of streams by sewage 
 is a matter of much difficulty, as may be further 
 illustrated by the assumed case of two cities 
 located on the same stream, from which each 
 
?O SEWAGE DISPOSAL. 
 
 derives its water supply and into which both dis- 
 charge sewage. 
 
 The city situated the further down the river 
 apprehends serious pollution of its water supply by 
 the sewage from the other city, and requests that 
 city to take measures to prevent pollution of the 
 water by purifying its sewage. The answer is : 
 " While we deplore the fact that your citizens 
 should feel apprehensive of danger because of 
 their water supply being contaminated by sewage 
 impurities from our city, we cannot concede 
 your request to be either equitable or consistent, 
 inasmuch as you enjoy the same privilege and 
 employ the same method of sewage disposal 
 as do we, to the detriment of the waters of the 
 river below you to an extent that may cause 
 apprehension on the part of your neighbor similar 
 to that which you feel towards this city. If you- 
 consider your present water supply unwholesome, 
 why do you not secure a new source of supply ? 
 If this be impracticable, then why do you not 
 purify the river water before using it ? 
 
 " Our sewerage system has already been a source 
 
DISPOSAL BY DILUTION. ? 'I 
 
 of heavy expense to us, and now to acquire sew- 
 age-disposal works of a capacity to admit of 
 purifying our sewage before turning it into the 
 river would require a large additional expendi- 
 ture of money. This additional cost, together 
 with the annual cost of maintenance and of oper- 
 ation of the disposal works, would be a constant 
 source of expense, which could only be met by 
 a direct tax upon our community ; for disposal 
 works cannot be, in so far as we may judge from the 
 experience of other cities, the source of any net 
 revenues. Our present method of sewage dis- 
 posal causes no one any nuisance; and to us it is a 
 method of great convenience. Any expenditures, 
 therefore, in disposal works are practically for the 
 purpose of securing to you immunity from 
 sewage impurities in a permanent and natural 
 water-course, which you have made a source of 
 water supply. Moreover, you are aware that the 
 volume ,of water that is daily consumed by any 
 community is about equal to the volume of 
 sewage that is daily discharged by it ; therefore 
 it should be easier, cheaper, and much more 
 
72 SEWAGE DISPOSAL. 
 
 efficacious to remove the organic impurity and 
 bacteria from any given quantity of the river 
 water which constitutes your water supply than 
 it would be for this city to remove very many 
 times the amount of the same organic im- 
 purity and the same variety of bacteria from 
 an equal volume of sewage. Furthermore, since 
 water is an article of use and is in demand by 
 every citizen of any town or city, every one is 
 willing to buy it delivered in his house, just as 
 he would buy any other necessity of life ; there- 
 fore a sufficient sum of money can be easily col- 
 lected by \vater rates to operate, maintain, and 
 eventually to pay for any water-purifying works 
 that you may construct." 
 
 Although this is an assumed instance, it illus- 
 trates the conditions of many cities in this 
 country with respect to water supplies and 
 sewage disposal, either as they exist to-day or as 
 they will exist but a few years hence ; and the 
 arguments in favor of sewage disposal into 
 streams, as presented, are very pertinent to the 
 general situation. It is even true that the latest 
 
DISPOSAL BY DILUTION. 73 
 
 information regarding the practicability of puri- 
 fying polluted water presents new and even 
 greater obstacles than ever to the prohibition of 
 sewage disposal into streams. How, then, can 
 the purity of public water supplies be secured ? 
 The best and most practicable method of water 
 purification is filtration through sand. Proof 
 that any infectious properties of sewage-polluted 
 waters may be removed by sand filtration may 
 be had by examining the results already attained 
 in practice in the filtration of public water sup- 
 plies. The city of London, which receives the 
 greater portion of its water supply from the 
 grossly sewage-polluted rivers Thames and Lea, 
 after sand filtration, has had an average of only 
 .46 per cent, of the total number of deaths from 
 typhoid fever between the years 1868 and 1880. 
 In the year 1892 the cities of London and 
 Berlin, both using for public water supplies 
 sewage-polluted river water after sand filtration, 
 were practically free from typhoid fever, having 
 had deaths from that cause of but .49 and .42 per 
 cent, respectively, of all the deaths for the year. 
 
74 SEWAGE DISPOSAL. 
 
 In Chicago the deaths from typhoid fever during 
 the years 1892 and 1893 were respectively 6.72 
 and 2.64 per cent, of the total deaths ; in Phila- 
 delphia in 1892 they were 2.22 per cent, of the 
 total deaths; in Boston in 1892 they were 1.22 
 per cent; in New York in 1892 they were .9 
 per cent; in Brooklyn in 1892 they were .8 per 
 cent. Not one of these five American cities 
 used filtered water with the exception of Brook- 
 lyn, which has a portion of its supply from 
 ground sources ; yet the death-rate from typhoid 
 fever is higher than in cities using sewage-pol- 
 luted water that had been filtered. The water 
 supplies of Chicago, Philadelphia, and a portion 
 of that of Boston were known to have been 
 more or less polluted by sewage at that time. 
 Moreover, several of these cities and other cities 
 of the United States are known to have had the 
 benefits of special legislative enactments to aid in 
 preserving the purity of their water supplies. 
 
 The city of Lawrence, Mass., is situated on the 
 Merrimack River, and takes its water supply from 
 that river about nine miles below the point where 
 
DISPOSAL BY DILUTION. 75 
 
 the city of Lowell discharges its sewage; and having 
 had annually many deaths from typhoid fever, that 
 city constructed a sand-filter with which to filter 
 the waters of the Merrimack River. This filter 
 was started in operation in September, 1893 ; and 
 for the three following months it removed 98 per 
 cent, of the bacteria of the river water and con- 
 verted a large part of the organic matter into harm- 
 less inorganic compounds. After two weeks' 
 storage of this filtered water in a storage reservoir 
 
 o o 
 
 and supply-mains there remained but one half of 
 one per cent, of the original bacteria in the water, 
 and these were of harmless varieties. Moreover, 
 there were during these months but four deaths 
 from typhoid fever ; whereas for the same months 
 of the preceding five years the average number 
 of deaths from the same cause was 18. In the re- 
 port of the Lawrence Water Board for 1893 it 
 is stated that " thus far the filter has performed its 
 work satisfactorily, the results of which are 
 already apparent to every user of city water. 
 From the day of letting on the water to the 
 present there has been a continuous and ample 
 
 
76 SEWAGE DISPOSAL. 
 
 supply of filtered water received into the pump- 
 wells and pumped into the reservoir. The con- 
 struction of this sand-filter has. proved the theory 
 that water can artificially be made pure and 
 wholesome; and from the best scientific advice we 
 now can say that the city of Lawrence enjoys the 
 benefits of as pure water as any city in the country." 
 With regard to the results of the experiments 
 in water purification by sand filtration of the 
 Massachusetts State Board of Health, it is stated 
 in the report of that board for 1892 that "the 
 results of experiments, which show that in all of 
 these filters adapted to the purification of drink- 
 ing-water more than ninety-nine and one half per 
 cent, of the applied bacteria were removed, to- 
 gether with the actual experience of many Euro- 
 pean cities having remarkably low death rates 
 from diseases known to be capable of conveyance 
 by drinking-water, while using filtered water 
 drawn from polluted sources, leave no room for 
 doubt as to the efficiency of such filtration, 
 when properly conducted, as a safeguard against 
 water-carried diseases." 
 
DISPOSAL BY DILUTION. 77 
 
 Thus we observe that the practical utility and 
 efficiency of slow sand filtration is established as 
 a means of removing bacteria, disease-germs, and 
 organic impurity from sewage-polluted waters. 
 
 And now it can be further asserted of sewage 
 disposal by dilution that it is not only impracti- 
 cable to prevent infection of waters by prohibit- 
 ing such a method of sewage disposal, but also, 
 as a general proposition and in the majority of 
 cases, it is wholly unnecessary to do so ; for it is far 
 better to insure the safe and potable qualities of a 
 water either polluted or liable to become polluted 
 by sewage by filtration immediately before use 
 rather than to resort to the questionable and 
 uncertain method of attaining the same end 
 by measures prohibitive of sewage disposal into 
 water. 
 
 In some instances it may be necessary to enact 
 and enforce measures to prevent the undue pollu- 
 tion of streams, just as ordinances are enforced by 
 cities to prevent the pollution of the atmosphere 
 by foul odors from accumulations of garbage, by 
 unwholesome and offensive smoke, and gases 
 
? SEWAGE DISPOSAL. 
 
 from public buildings, manufactories, and other 
 industrial works, or just as a nuisance would be 
 abated. But in the light of our present knowledge 
 of the natural processes at work in the purification 
 of polluted waters, and of our ability to make 
 practical application of these processes in sewage 
 disposal and in the purification of water supplies, 
 there is less occasion than ever of any general 
 and far-reaching legislation directed either to the 
 regulation or the prohibition of sewage disposal 
 by water. Legislative action upon this and kin- 
 dred matters will be of far more public benefit 
 if directed to the collection and systematizing of 
 those data from a practical as well as scientific 
 standpoint as will admit of a more thorough and 
 general knowledge of the involved natural laws 
 and processes and the application of them to use- 
 ful purposes, and to the subsequent dissemination 
 of this knowledge. 
 
 Before concluding this chapter it is necessary 
 to especially refer to the sewage disposal of many 
 inland towns which are so situated as to have 
 neither large nor permanent streams into which 
 
DISPOSAL BY DILUTION. 79 
 
 to discharge sewage. Such towns, when sup- 
 plied with both public water supplies and sewer- 
 age, need not necessarily be constrained to treat 
 the sewage because of the want of such disposal 
 facilities. For it may be quite practicable, at 
 least in some instances, by means of water im- 
 pounded in a reservoir above the sewer outfall 
 to maintain a continuous and uniform flow in 
 a stream that may occasionally go dry, and to 
 periodically flush out the channel of any ac- 
 cumulated deposits. But even without such 
 natural advantages for flushing and diluting reser- 
 voirs of water and in the absence of facilities 
 or financial ability to construct, maintain, and 
 operate disposal works of any kind, it is much 
 safer and better to temporarily turn the crude 
 sewage into the channel-way of such non-per- 
 manent stream at some point that may be 
 sufficiently far removed from habitations to pre- 
 vent resulting offence, than to retain it in either 
 tight or leaching cesspools ; for, if so discharged 
 into the channel of a stream of this kind, much of it 
 will flow away, the suspended matter in sewage that 
 
80 SEWAGE DISPOSAL. 
 
 may deposit will be greatly distributed, and the 
 organic vapors and any gases of putrefaction 
 that may be given off will be more distributed, 
 more diluted with pure fresh air, and consequent- 
 ly much less objectionable to a community from 
 any standpoint from which this method of dis- 
 posal can be viewed than if confined in cesspools 
 from which very offensive gases of putrefaction 
 are exhaled in close proximity to dwellings. 
 Moreover, the danger of polluting subsoil waters 
 by the one practice is far less than by the other ; 
 for any sewage that may filter into the soils from 
 the bed of a small stream will be subject to the 
 immediate purifying influences of porous soils 
 to a far greater degree than if it filtered from a 
 defective or a leaching cesspool into and through 
 the subsoils. Furthermore, the bed of such a 
 stream will be cleaned quite as often and quite as 
 thoroughly by the occasional flushing that it may 
 receive from storm-waters as will the cesspool, 
 when subject to no greater vigilance or to no 
 more rigid enforcement of city ordinances regu- 
 lating the cleaning and disinfecting of cesspools 
 
DISPOSAL BY DILUTION. 8 1 
 
 than is usually exercised by municipal authorities. 
 
 On the whole, it may be said of sewage dis- 
 posal by dilution that it is the simplest, most 
 economical, most expeditious method of sewage 
 disposal that has yet been tried ; and it is as fully 
 efficacious as any when the self-purifying powers 
 of water are duly regarded. 
 
 The objections that have been raised to the 
 method are not, in many instances, valid ; for 
 many of them are based upon a wrong rather 
 than a proper application as when more sewage 
 is committed to a stream than it has the volume 
 of flow to sufficiently dilute, remove, and purify. 
 
82 SEW GE DISPOSAL. 
 
 CHAPTER IV. 
 
 DISPOSAL OF SEWAGE BY IRRIGATION. 
 
 SEWAGE disposal by irrigation consists in the 
 application of raw sewage to land for the pur- 
 pose of raising crops. At the time of the origi- 
 nal application of irrigation to the disposal of 
 sewage, great stress was laid upon the manurial 
 value of sewage ; its advocates arguing that the 
 nitrogen, phosphoric acid, and potash salts, which 
 are constituents of sewage and which are essen- 
 tially plant-foods, could and should he utilized in 
 the production of crops. 
 
 In line with this view many scientists of 
 England had attempted by chemical analysis to 
 demonstrate the commercial value of these con- 
 stituents as fertilizers. For instance, by one in- 
 vestigator the yearly solid and liquid excretia of 
 one adult was estimated 'to yield 16.41 pounds of 
 nitrogen an amount that was sufficient, it was 
 
DISPOSAL OF SEWAGE BY IRRIGATION. 83 
 
 said, to fertilize 800 pounds tff wheat, rye, or 
 oats, or 900 pounds of barley, and was equivalent 
 to 75 pounds of Peruvian guano. Hofmann and 
 Witt estimated the manurial value of one ton of 
 London sewage to be about 4 cents ; Lawes and 
 Gilbert, 4 to 5 cents ; Bailey Denton, 3^ cents. 
 Brady and Montague estimated Londoli sewage 
 to be worth annually about 14 million dollars, 
 while still another eminent authority placed the 
 annual value at about 20 million dollars.* Al- 
 though these estimates were necessarily theoreti- 
 qal, having been based upon the results of chemi- 
 cal analyses in the laboratory of sewage, soils, 
 and plants, still they had the indorsement of 
 such eminent scientific authority that it was but 
 natural to have attempted the utilization of the 
 manurial elements of sewage by applying the 
 sewage to the growing crops of farm-land. 
 These attempts have demonstrated the available 
 fertilizing properties of sewage Jo be far less than 
 had been predicted of them as a result of labora- 
 tory experiments ; for they yielded no profitable 
 
 Vide "The Treatment of Sewage" by Dr. C. Meymott Tidy. 
 
84 SEWAGE DISPOSAL. 
 
 increase to the productions of the farms, and 
 established the fact that there is a wide difference 
 between the theoretical and the commercial value 
 of sewage. Moreover, they have clearly indi- 
 cated two distinct aspects to the disposal of sew- 
 age by irrigation namely, the sanitary and the 
 commercial aspect. 
 
 On the one hand, the sanitary aspect of sew- 
 age irrigation has been shown to exact the 
 prompt, continuous, and inoffensive disposal of 
 the sewage upon the land, and thus to enforce 
 almost continuous and unseasonable irrigation, 
 and to compel the growing plants and the soils 
 to evaporate and to absorb a very large amount 
 of water in order to become possessed of the 
 manurial properties of the sewage. On the 
 other hand, the commercial aspect of sewage irri- 
 gation has been shown to demand inexpensive 
 methods of distributing the sewage upon the 
 land, and to require both seasonable and inter- 
 mittent irrigation and fertilization of crops. 
 
 Thus the farmer in his efforts to render sew- 
 age irrigation profitable and at the same time to 
 
DISPOSAL OF SEWAGE BY IRRIGATION. 85 
 
 duly regard the sanitary conditions exacted of 
 him, found himself in a dilemma : for if he irri- 
 gate continuously he must ruin his best and 
 most profitable crops, or if he fail to irrigate 
 continuously he must neglect the prompt and 
 proper handling of the sewage, and thus become 
 liable to prosecution for creating a nuisance. 
 
 As a result of the experience in England of 
 sewage disposal by irrigation, it is shown that 
 such a method of disposal is incompatible with 
 the attainment both of a profit from a sewage- 
 farm and of good sanitary conditions upon it ; 
 that as a private enterprise sewage-farming is a 
 signal failure ; and that municipal control of a 
 sewage-farm is necessary if it be operated in the 
 interests of sanitation. 
 
 The amount of land that may be required for 
 sewage irrigation and the expense of preparing 
 it cannot be determined by any fixed rule. 
 Smooth ,and gently-sloping land affords an easy 
 and comparatively economical distribution of the 
 sewage. A close, fine-grained and retentive soil 
 can naturally take care of much less sewage than 
 
86 SEWAGE DISPOSAL. 
 
 can a free and porous one. If the purpose be 
 a complete utilization of the sewage, in other 
 words, the application of just so much sewage to 
 land as can be readily appropriated, absorbed, 
 and evaporated by growing plants, as is the case 
 where land is used for market gardening, a much 
 larger acreage of land will be required than 
 though the land were kept saturated with sew- 
 age, as is usually the case in broad irrigation of 
 grass-lands. 
 
 The published results of sewage irrigation in 
 England, where the average daily water consump- 
 tion is about 40 to 50 U. S. gallons for each 
 inhabitant, is to the effect that for complete 
 utilization of sewage one acre of ground is re- 
 quired for every 30 to 50 inhabitants, but when 
 thorough sanitary precautions may in a measure 
 be disregarded, that an acre of ground will an- 
 nually take care of an average of 5000 to 7000 
 tons of sewage, the equivalent of about 100 in- 
 habitants. 
 
 Mr. Kuechling, in the Transactions of Am. 
 Soc. C. E. of January, 1888, states with respect 
 
DISPOSAL OF SEWAGE BY IRRIGATION. 87 
 
 to the extensive sewage-farms of Berlin, Ger- 
 many, which among others he visited in 1884, 
 that sewage irrigation was commenced with a 
 proportion of 250 persons per acre, which pro- 
 portion was in the succeeding years reduced to 
 100 per acre; and that "the director of the 
 farms, a highly-cultivated gentleman, stated that 
 the tendency was to still further reduce the amount 
 of sewage put upon the land. He hoped to get 
 it down to a basis of 75 persons per acre per year, 
 but preferred to reduce it to 50. ... By such 
 reduction he hoped to make a slight profit, also 
 to do away with the alleged pollution of the sub- 
 soil waters and effect the abatement of the stench 
 nuisance that occurs on all sewage-farms at 
 pretty much all seasons of the year." 
 
 The effect of sewage irrigation upon the 
 healthfulness of the locality adjacent to sewage- 
 farms and upon the farm itself does not appear 
 to be fully established, because statistical infor- 
 mation in matters of this kind is difficult of ac- 
 cess, and to be of much value it is necessary 
 that observations be carefully recorded during 
 
88 SEWAGE DISPOSAL. 
 
 a considerable period of years. However, the 
 summation of the evidence thus far recorded 
 seems to be to the effect that sewage irrigation is 
 not injurious to health provided the sewage be 
 fresh when applied to the land. 
 
 With respect to the exhalation of offensive 
 vapors and odors from sewage-irrigated land, 
 there seems to be a considerable difference of 
 opinion among those who have visited sewage 
 farms. Some assert that no offensiveness pre- 
 vails, while others with apparently as good op- 
 portunity of judging positively affirm the con- 
 trary. These differences of opinion may in 
 a measure be due to differences of individual 
 judgment as affected by the aesthetic tastes and 
 the imagination ; consequently, what one might 
 consider offensive another would not. Even the 
 same individual visiting a farm at different sea- 
 sons of the year may form very different opinions 
 regarding its offensiveness or non-offensiveness ; 
 for the variation in temperature and relative 
 humidity of the atmosphere, the state of the 
 growing crops, whether luxurious or not, and 
 
DISPOSAL OF SEWAGE BY IRRIGATION. 89 
 
 other changeable conditions about a sewage-farm 
 may be the cause of very different sensations. 
 In fact, there seems to be no other way of recon- 
 ciling the conflicting views that have been ex- 
 pressed upon this subject. 
 
 There seems, however, to be no good grounds 
 of expecting sewage-farms, even under the best 
 of management, to be entirely free from odor ; 
 for even from fresh sewage a musty and somewhat 
 offensive odor is exhaled. So far as is known 
 no ill effects have followed the inhaling in the 
 open air of these organic vapors from fresh sew- 
 age, and the musty odor which is characteristic of 
 them soon disappears by air dilution. 
 
 If by any neglect or mismanagement sewage 
 be allowed to pond upon the surface of the 
 ground, or sludge be permitted to collect either 
 upon the stalks of the growing plants or upon 
 the ground, there will result in a warm, humid 
 atmosphere putrefactive decomposition of the 
 organic impurity, causing offensive odors. There- 
 fore the sanitary condition of any sewage-farm 
 depends quite as much upon the management 
 
9 SEWAGE DISPOSAL. 
 
 of the farm as upon the character of the sewage 
 that is applied to the land. 
 
 The pollution of subsoil water has been re- 
 garded in several instances as the result of sewage 
 irrigation. Doubtless if the land be kept almost 
 continuously flooded with sewage, as is the case 
 with broad irrigation, the subsoil waters may 
 become polluted ; but if the sewage be applied 
 to the land intermittently, so that the soil may be 
 aerated and cultivated, as would be the case in 
 the complete utilization of sewage, it does not 
 appear probable that pollution will affect the sub- 
 soil water. For irrigation, in that event, becomes 
 combined with intermittent filtration, and the 
 conditions are thereby rendered favorable for the 
 natural purification of any sewage that may seep 
 into the ground. 
 
 The United States, lying as it does between 
 the fifteenth and the twenty-fifth degrees of lati- 
 tude and between the sixty-seventh and one hun- 
 dred and twenty-fifth meridians, and with eleva- 
 tions varying between the extremes of sea-level 
 and the highest peaks of the Sierra Nevada and 
 
DISPOSAL OF SEWAGE BY IRRIGATION. 9! 
 
 Rocky Mountains, and with a geology repre- 
 senting the oldest as well as the most recent for- 
 mations, and with a range of mean annual tem- 
 perature from 41 to 72 degrees Fahrenheit, must 
 possess conditions of climate and atmosphere, of 
 soil and topography, more varied than can be 
 found in almost any other country. 
 
 The rainfall over this country has a great range 
 of seasonal distribution, and varies from a mean 
 of 4 inches to 94 inches per annum. Its distribu- 
 tion is such that in almost any portion of the 
 United States east of the one hundredth meridian 
 the production of good crops is almost annually 
 assured. But from this meridian to the Pacific 
 Ocean, excepting a strip of territory along the 
 northwestern coast, and from the northern to the 
 southern boundary of the country, there is a vast 
 territory of about 1,300,000 square miles, or of 
 about four tenths of the entire area of the United 
 States, that is dependent for agriculture almost 
 entirely upon irrigation. OT this arid territory 
 there is an area of about 126,000 square miles that 
 has a mean annual rainfall of less than 10 inches, 
 
92 SEWAGE DISPOSAL. 
 
 and about 259,000 square miles over which it is 
 between 10 and 15 inches. 
 
 The main drainage of the eastern and south- 
 eastern coast country is by many rivers and 
 tributaries of moderate length and of heavy 
 average slope ; while that of the central or Mis- 
 sissippi River basin is by rivers of great length 
 and of moderate average slope, bearing vast 
 quantities of silt and debris. The rivers of the 
 so-called arid country west of the one hundredth 
 meridian are in some respects quite in contrast 
 with those just described ; for they flow from 
 their mountain source through deep canons into 
 the plains, where they spread out in thin sheets 
 over broad sandy beds, or divide into various 
 small shallow streams. In dry hot weather 
 they almost disappear in the sands. Few, if any, 
 of their tributaries are perennial streams. Thus, 
 in a country as varied in its characteristics as is 
 the United States it is not at all probable that 
 the results of experience of foreign countries in 
 sewage disposal by irrigation will be found appli- 
 cable, excepting, perhaps, in those districts of 
 
DISPOSAL OF SEWAGE BY IRRIGATION. 93 
 
 similar climatic and meteorological condi- 
 tions. 
 
 Although it may be somewhat difficult to an- 
 ticipate the ex'ent to which sewage disposal by 
 irrigation may become popular in the United 
 States, yet it may be fairly assumed that in the 
 localities where soil, climate, and rainfall favor 
 the annual production of good crops it is by 
 itself of exceedingly questionable utility. More- 
 over, it is very probable, especially with respect 
 to large cities, that the acquirement of a suffi- 
 cient amount of land under municipal ownership 
 or control for such a purpose will be found ex- 
 ceedingly difficult ; for instance, a city of 30,000 
 inhabitants will by the best authorities in Eng- 
 land require about 300 to 600 acres of land, the 
 number of acres depending upon the complete- 
 ness of the utilization of sewage. But this re- 
 lation of acreage to the number of inhabitants 
 would not necessarily follow in this country: for 
 here the average daily water consumption is from 
 two to three times greater than in England ; con- 
 sequently, there will be needed a somewhat greater 
 
94 SEWAGE DISPOSAL. 
 
 acreage of land. Furthermore, there are the dis- 
 advantages of the additional expense of culti- 
 vating sewage-irrigated land over that of culti- 
 vating non-irrigated land ; of the offence associ- 
 ated with the handling of sewage; and of the com- 
 mercial losses almost sure to ensue all of which 
 render this method of sewage disposal more or 
 less unpopular in localities where irrigation is not 
 naturally needed, and quite cumbersome and im- 
 practicable with respect to large and populous 
 cities. Small inland towns, which have no streams 
 available into which they may permanently dis- 
 charge sewage, may find in sewage irrigation a 
 method of some utility ; for, the volume of sewage 
 to be disposed of being small, it is quite probable 
 that a sufficient amount of land can be acquired 
 near the town by purchase or rental for a reason- 
 able expenditure of money to effectually dispose 
 of the sewage at least for that portion of the 
 year when sewage might become offensive if dis- 
 charged directly into a stream of insufficient vol- 
 ume to properly dilute it. But any value which 
 this method of sewage disposal may have will be 
 
DISPOSAL OF SEWAGE BY IRRIGATION. 95 
 
 most appreciated by towns in a locality where ir- 
 rigation is a necessity ; not that sewage possesses 
 manurial properties, nor that its application to 
 land is scientifically proper, but rather because 
 water having become an urgent necessity is ac- 
 ceptable in any condition. In such localities it 
 is quite probable that sewage may be quite com- 
 pletely utilized for farm irrigation at seasonable 
 times ; because, the local demand for all garden 
 and farm produce being naturally great, the sew- 
 age will in all probability be given a wide distri- 
 bution over the land in order to avoid over-irri- 
 gation and a resulting injury to the growing 
 crops. 
 
 The complete utilization of sewage is appar- 
 ently the only truly sanitary method of sewage 
 disposal by irrigation. This, however, is only 
 practicable during the productive seasons of the 
 year, and by intermittent irrigation ; for at such 
 seasons and by this method the commercial and 
 sanitary aspects of sewage irrigation may be made 
 most nearly to harmonize. But when the irriga- 
 tion season is over, and until it shall have re- 
 
g SEWAGE DISPOSAL, 
 
 turned, it is quite probable that in the majority of 
 cases the commercial interests alone will largely 
 determine the disposition to be made of the sew- 
 age. 
 
 The practice of the city of Pullman, Illinois, 
 near Chicago, with a population of 12,000 in- 
 habitants, has frequently been referred to as an 
 instance of the successful disposal of sewage by 
 irrigation ; but the evidence thus far made pub- 
 lic does not sustain the view of successful prac- 
 tice for that city ; for it indicates that for a con- 
 siderable portion of each year the crude sewage 
 is turned into Lake Calumet, and that the appli- 
 cation of other fertilizers than sewage has been 
 found more profitable upon the corporation 
 farm. 
 
 Even in foreign countries the practicability of 
 utilizing the manurial properties of sewage is con- 
 sidered doubtful. How much less in this country, 
 where the dilution of sewage in towns having a 
 bountiful water supply is so great that the organic 
 impurity seldom exceeds one part in two thou- 
 sand parts of sewage, should it be expected to de- 
 
DISPOSAL OF SEWAGE BY IRRIGATION. 97 
 
 rive any practical benefits from sewage as a fer- 
 tilizer! 
 
 But attaching to sewage a value in those por- 
 tions of the United States susceptible of successful 
 irrigation, it is even then scarcely to be antici- 
 pated that irrigation as a means of sewage dis- 
 posal can be successful without considerable ex- 
 penditure of money, either to compensate those 
 who may be induced to take care of the sewage 
 at unseasonable periods for irrigation, both for 
 services and for the rental of lands, or to acquire 
 and to make use of facilities for disposing of 
 the sewage at intervals by other methods than by 
 irrigation. Thus far there 'is nothing in the ex- 
 perience either in this country or in foreign coun- 
 tries to conclusively indicate that the productions 
 of a sewage-farm will be the source of net profit, 
 though the income derived from the sale of them 
 will materially reduce operating expenses. 
 
 On the whole, from the standpoint of complete 
 utilization of sewage, it appears highly probable 
 that sewage irrigation will be quite unpopular in 
 the naturally productive sections of the country, 
 
98 SEWAGE DISPOSAL. 
 
 excepting it may be among some of the small 
 inland towns and cities, which may successfully 
 apply sewage to land during the growing seasons 
 of the year. The method is more adapted to an 
 irrigating country. But in any event it will be 
 quite necessary to associate with sewage irrigation 
 other methods of sewage disposal that will be 
 effective where irrigation becomes impracticable, 
 as it will for a period of each year. 
 
 There can be no definite rules laid down to 
 guide in the selection of proper land for sewage 
 irrigation, or in the laying out of a sewage-farm. 
 Generally it is preferable that the soil be light, 
 open, porous, and well drained ; but in practice 
 such land as may be available must be used, and 
 if it does not naturally possess the ideal condi- 
 tions for successful sewage irrigation it must be 
 artificially improved. If the soils be variable in 
 character it is advisable to subdivide the farm 
 with reference to these varying qualities of soil, 
 in order to bring together as much as possible 
 in beds and plats soils of equal producing, ab- 
 sorbing, and purifying characteristics. Such a 
 
DISPOSAL OF SEWAGE BY IRRIGATION. 99 
 
 subdivision can be readily made by earth em- 
 bankments. 
 
 Usually the sewage is brought to the irrigation 
 farm in pipes and carried to the various subdivisions 
 of the farm by earth or masonry-lined open carriers, 
 and from these carriers distributed over the ground 
 through earth trenches or by broad irrigation. The 
 carriers should be so elevated above the surface of 
 the surrounding ground as to be easily drained; 
 otherwise the detention of sewage within them 
 may cause offence. The vapors from fresh sewage 
 flowing in open carriers need be the source of no 
 apprehension, for they quickly become diluted 
 by the atmosphere. 
 
 The method of conducting the sewage under 
 pressure through closed subsurface pipes and of 
 applying it to the growing crops by sprinkling 
 through hose and nozzle attached to hydrants 
 connecting with the pipe system is one which is 
 sometimes advocated because of the uniform dis- 
 tribution of sewage that can be thus attained, 
 but which is largely impracticable because of the 
 heavy expense involved in pressure subsurface 
 
100 SEWAGE DISPOSAL. 
 
 pipe-carriers and the necessary attachments, be- 
 cause of the cost of labor in applying the sewage, 
 and because of the sanitary objection to throwing 
 crude sewage upon the leaves and stalks of grow- 
 ing vegetation. 
 
 The details and general arrangement of a sew- 
 age-farm should be as simple and inexpensive 
 as possible ; therefore every possible advantage 
 should be taken of the slopes and configuration 
 of the ground, and of the variable absorbing 
 powers of the soils. The fields and plats should 
 be so graded that the ponding of sewage will be 
 obviated ; otherwise the putrefaction of ponded 
 sewage may cause a serious nuisance. The ar- 
 rangement of carriers should facilitate the prompt 
 delivery of sewage to any part of the farm, and 
 the quick and uniform distribution of it over any 
 plat or field. As a general rule the more porous 
 the soil of any farm or subdivision of a farm 
 may be, the greater should be the number of car- 
 riers and the smaller should be the size of the 
 individual field or plat to be irrigated ; for it is 
 evident that the more porous a ground may be 
 
DISPOSAL OF SEWAGE BY IRRIGATION. IOI 
 
 the more readily it will absorb, and the greater 
 its absorbing power the more rapidly should the 
 sewage be distributed over it. This can be ac- 
 complished in a practical manner only by having 
 numerous carriers and small plats of ground. 
 
 To what extent auxiliary means of disposing 
 of sewage at times unseasonable for irrigation 
 may have to be provided, and the character of 
 these auxiliaries, and whether settling-tanks shall 
 be used to remove some of the heavier sus- 
 pended matters in the sewage before irrigation, 
 and whether underdrainage of any part or parts 
 of the field shall be necessary, are all matters for 
 local and special consideration. The mechanical 
 details can be readily worked out when once the 
 general outlines of an irrigation farm are devel- 
 oped in accordance with the general principles 
 that have just been outlined. 
 
 What may have been accomplished in some 
 localities, and the methods which may have been 
 there employed, are matters of general interest 
 rather than of general guidance in special cases. 
 Therefore the arrangement of a sewage-irrigation 
 
 
 
102 SEWAGE DISPOSAL. 
 
 farm and the design of its different parts and 
 details that may have been successful in one 
 instance is no criterion in another instance except 
 - to the extent of identical natural conditions and 
 advantages. 
 
DISPOSAL B Y INTERMITTENT FIL TRA TION. 103 
 
 CHAPTER V. 
 
 DISPOSAL OF SEWAGE BY INTERMITTENT FIL- 
 TRATION. 
 
 FILTRATION is popularly understood to be a 
 simple straining process, whereby a liquid having 
 matters in suspension is relieved of them and 
 becomes more or less clarified by percolating 
 through some porous substance. This impression 
 so far at least as it relates to the filtration of 
 polluted water fails to comprehend the most im- 
 portant function of filtration, inasmuch as a filter 
 which is properly constructed and operated pos- 
 sesses the property of removing organic impurity 
 dissolved in water by a process of natural purifi- 
 cation. The process is a natural one, because it 
 depends upon the prevalence of certain natural 
 conditions for its successful procedure, as, e.g., the 
 presence both of oxygen and of living micro- 
 organisms. 
 
IO4 SEWAGE DISPOSAL. 
 
 It is well known that a percentage of the vol- 
 ume of any porous material consists of voids or 
 open spaces between the individual particles. 
 Now if a porous material be properly selected 
 and made into a filter, a liquid in percolating 
 through it becomes subdivided into innumer- 
 able fine streams which partially occupy the 
 voids of the filter or channelways. Thus a 
 large surface of the liquid is exposed to con- 
 tact with the air also contained within the 
 filter, which affords favorable conditions for the 
 natural oxidation of the dissolved organic im- 
 purity. In time the air becomes exhausted from 
 the filter, and then the only available oxygen 
 for purification is that which may be in solution 
 in the liquid being filtered. If this liquid be 
 sewage, which is known to have no dissolved 
 oxygen, the purifying power of the filter ceases 
 the moment the air supply is exhausted ; conse- 
 quently it becomes necessary to cease at inter- 
 vals the application of sewage, in order that the 
 sewage may drain from the filter, and that the 
 air may enter and fill the voids thus vacated. By 
 
DISPOSAL BY INTERMITTENT FILTRATION. IO5 
 
 this means filtration becomes intermittent, which 
 term implies an alternate filling of the voids of 
 the filtering material with sewage and with air. 
 
 The difference between irrigation as treated 
 in the preceding chapter, and intermittent filtra- 
 tion as here considered, is that in the former 
 case the sewage which is applied to the land is in 
 proportion to an amount which the growing 
 plants will absorb, while in the latter case it is in 
 proportion to an amount which the land will 
 naturally absorb and purify ; the purified effluent 
 being permitted to drain away through porous 
 subsoils or collected into subsurface drains which 
 discharge into a neighboring stream or ravine. 
 
 The practical value of intermittent filtration in 
 its application to the purification of sewage was 
 first recognized in 18/0 by the Rivers Pollu- 
 tion Commission of England, as a result of the 
 investigations of its chemist, Dr. Frankland. 
 Since that date it has been put to practical 
 test in several foreign cities ; and its principles 
 have been subjected to more or less searching 
 investigation by various scientists. Prominent 
 
106 SEWAGE DISPOSAL. 
 
 among these investigations are those of the State 
 Board of Health of the State of Massachusetts. 
 That board, by legislative authority, commenced 
 a set of experiments in 1888, which are yet in 
 progress, with a view of arriving at a thorough 
 and complete knowledge of all the facts and 
 principles involved in this process of purification, 
 and of determining its practical utility in that 
 State. The author has freely quoted from the 
 records of this board, in order to outline the 
 utility of intermittent filtration for the disposal 
 of sewage, and because they are more complete 
 and comprehensive than any previous experi- 
 ments. 
 
 With respect to filtering materials, the board 
 states that : " With the gravels and sands, from 
 the coarsest to the finest, we find that purifica- 
 tion by nitrification takes place in all, when th.e 
 quantity of sewage is adapted to their ability, and 
 the surface is not allowed to become clogged by 
 organic matter to the exclusion of air. 
 
 " With fine soils, containing, in addition to 
 their sand-grains, two or three per cent, of alu- 
 
DISPOSAL BY INTERMITTENT FILTRATION. JO/ 
 
 minia and oxide of iron and manganese and six 
 or seven per cent, of organic matter, we find that, 
 when only six inches in depth, resting upon fine, 
 sandy material, they retain water so long that the 
 quantity that can be applied is so small, and the 
 interval in which this must settle and dry away 
 to allow air to enter the filter is so long, that the 
 amount of sewage that can be purified is very 
 small. When the quantity applied is adapted to 
 its ability, such a filter may give an excellent 
 effluent, quite free from bacteria. 
 
 " With greater depths of soil the quantity that 
 can be filtered will evidently become less ; and, 
 with the depth of five feet of such a soil we have 
 found nitrification did not take place ; and, although 
 it is probable that no bacteria came through, 
 the organic matter in the effluent was, at the 
 end of two years, nearly as great as in the sewage. 
 This soil remained continually so nearly saturated 
 that, when only 5030 gallons per acre were being 
 filtered daily, although free to drain over every 
 square foot of the bottom, sufficient air could not 
 be taken in to produce any nitrification ; and the 
 
108 SEWAGE DISPOSAL. 
 
 chemical results with this material was, through- 
 out the two years of its trial, nearly the same as 
 would be expected if the filtration had been made 
 continuous instead of intermittent. 
 
 "With peat upon the surface of a filtration 
 area, even to the depth of only one foot, its im- 
 perviousness to liquid, and the quantity that it 
 will retain until it evaporates, renders intermit- 
 tent filtration impracticable ; and a sand area 
 thus covered with peat can be rendered efficient 
 for filtration only by the removal of the peat from 
 the surface." 
 
 In order to prove that intermittent filtration 
 is not a straining process, and that it does not 
 depend upon the size of the sand-grains, the 
 board had constructed a filter five feet in depth, 
 in which the filtering material was of washed 
 gravel-stones the size of beans, from which all 
 sand had been screened. The filter was operated 
 for nine months, filtering daily the equivalent of 
 81,400 gallons of sewage per acre, resulting in an 
 average analysis of the effluent from this filter 
 during the last two months of the period that 
 
DISP OSAL BY IN TERM I T TEN T FIL TRA TION. 1 09 
 
 showed 98.6 per cent, of the organic impurity 
 and 99 per cent, of the bacteria to have been re- 
 moved from the sewage. Then for a succeeding 
 three-months the quantity of sewage applied to 
 the filter was the equivalent of 126,000 gallons 
 per acre per day, with a resultant effluent, the 
 average for the last month, indicating that 98.5 
 per cent, of the organic impurity and 99.6 per 
 cent. of the bacteria had been removed. 
 
 The Board of Health, in conclusion, states that: 
 " These results show more definitely than any 
 others the essential character of intermittent fil- 
 tration. We see that it is not a straining pro- 
 cess. By the application of a small quantity of 
 sewage over the whole surface of the tank each 
 hour, each stone in the tank was kept covered with 
 a thin film of liquid, very slowly moving from stone 
 to stone, from the top towards the bottom, and 
 continually in contact with air in the spaces be- 
 tween the stones. The liquid, starting at the top 
 as sewage, reached the bottom within twenty-four 
 hours, with the organic matter nearly all burned 
 out. The removal of this organic matter is in 
 
1 10 SEWAGE DISPOSAL. 
 
 no sense a mechanical one of holding back ma- 
 terial between the stones, for they are as clean as 
 they were a year ago ; but it is a chemical change, 
 aided by bacteria, by which the organic substances 
 are burned, forming products of mineral matter, 
 which pass off daily in the purified effluent. 
 
 "The liquid flowing out at the bottom is a 
 clear, bright water, comparing favorably, in every 
 respect that can be shown by chemical or biologi- 
 cal examination, with water from some of the 
 wells on the streets of our cities that are used for 
 refreshing draughts by the public during the sum- 
 mer." 
 
 Of the general results of intermittent filtration 
 of sewage, the Board of Health states that : 
 " Filter-tank No. i, which is one of the original 
 filters, and has been in use four years, has fil- 
 tered sewage during the past two years 1890 and 
 1891 at an average rate of 85,920 gallons per 
 acre daily for every day in that time, and with a 
 removal of 94 per cent, of the organic matters, 
 as shown by the albuminoid ammonia, and 98 
 per cent, of the bacteria. Filter-tank No. 2, also 
 
DISPOSAL BY INTERMITTENT FILTRATION. Ill 
 
 one of the original filters, has filtered for the 
 same period at an average rate of 49,360 gallons 
 per acre daily, and has removed 97.5 per cent, of 
 the organic matters and at least 99.99 per cent, 
 of the bacteria of the applied sewage. With 
 many other filters correspondingly good results 
 have been obtained." 
 
 The basis of judgment regarding the degree of 
 purification of sewage attained by intermittent 
 filtration is, with respect to the organic impurity, 
 the extent to which the ammonias representing 
 this impurity are changed into nitrates, harm- 
 less inorganic compounds, caused by the reaction 
 of the nitric acid formed by the bacterial oxida- 
 tion of the ammonias upon some of the minerals 
 dissolved in sewage ; and, with respect to the 
 living organisms common to sewage, the extent 
 to which these bacteria are removed, or their 
 vital activities arrested, as determined by bacte- 
 riology. The process of change among the ni- 
 trogenous constituents of sewage is technically 
 known as " nitrification," of which a concise de- 
 scription will be found in Chapter II. 
 
112 
 
 SEWAGE DISPOSAL. 
 
 The mechanical composition of the sands that 
 are considered the best suited for filtration may 
 be judged of by the following table, in which 
 " the figures given show the per cent, by weight 
 of the different materials having smaller diame- 
 ters than the sizes given in the first column " : 
 
 MECHANICAL COMPOSITION OF FILTERING 
 MATERIALS.* 
 
 
 
 
 
 Per( 
 
 lent. 
 
 
 
 
 Diameters in Millimeters. 
 
 Filter 
 No. 5. 
 
 Filter 
 No. 4. 
 
 Filter 
 No. 2. 
 
 Filter 
 
 No. 9. 
 
 Filter 
 
 No. 6. 
 
 Filter 
 No. i. 
 
 Filter 
 No 5 A 
 
 Filter 
 No.i6 
 
 
 
 
 
 
 8-2 
 
 
 
 98 
 
 62 
 
 06 
 
 
 
 
 73 
 
 97 
 
 95 
 
 27 
 
 
 Q2 
 
 
 
 
 
 85 
 
 
 
 .08... 
 
 80 
 
 
 
 IOO 
 
 32 
 
 53 
 
 4 
 
 
 46 . 
 
 80 
 
 
 ICO 
 
 
 
 
 
 
 24 
 
 6? 
 
 
 
 26 
 
 
 i 5 
 
 
 
 .12 
 
 06 
 
 5 1 
 
 85 
 
 43 
 
 3 
 
 4 
 
 
 
 I.O 
 
 0.5 
 
 
 
 
 11 
 
 
 
 
 
 
 
 
 
 6 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 "These materials may be said to include the 
 whole range of sands available for sewage purifi- 
 cation. Anything as fine as No. 5 is too fine for 
 advantageous use, while at the other end it would 
 hardly be safe to depend upon a gravel coarser 
 
 * Report of 1891, Mass. State Board of Health, 
 
DISPOSAL B Y INTERMITTKN7^ FIL TRA T1ON. 1 1 
 
 than No. 16, with a filtering stratum not over 5 
 or 6 feet in thickness. 
 
 " With the mixed materials, Nos. 5 and 6, the 
 smaller particles fill the spaces between the larger, 
 and these finer portions determine the capillary 
 attraction of the filter, its resistance to the pas- 
 sage of sewage, and, in fact, its action in every 
 way. The appearance of No. 6 is coarser than 
 No. i, and the average size of its particles is 
 greater, but its finest portion determines its char- 
 acter as a filter, so that it is practically finer than 
 No. i." 
 
 SIZE AND UNIFORMITY OF FILTERING MATERIALS.* 
 
 Number of Filter. 
 
 Ten per Cent of 
 
 Material Finer than 
 (Millimeters). 
 
 Uniformity 
 Coefficient. 
 
 Albuminoid 
 Ammonia. 
 Parts per 100,000. 
 
 No. 5 
 4 
 
 2 
 
 O.O2 
 0.03 
 0.06 
 
 9 
 2-3 
 2-3 
 
 95-0 
 18.0 
 0. 9 
 
 9 
 6 
 
 i 
 
 0.17 
 
 0-35 
 0.48 
 
 2.0 
 
 7.8 
 2.4 
 
 0.7 
 0.8 
 
 0.4 
 
 5A 
 16 
 
 I.4O 
 5-00 
 
 2.4 
 1.8 
 
 0.5 
 0.3 
 
 Report of 1891, Mass. State Board of Health. 
 
SEWAGE DISPOSAL. 
 
 In the table on page 113 " uniformity coeffi- 
 cient" is a term used to designate the ratio of 
 the size of the grain which has 60 per cent, of 
 the sample finer than itself to the size whicn has 
 10 per cent, finer than itself. "Albuminoid am- 
 monia" represents the organic matter natural to 
 the material of the filter. The heavy lines across 
 this table* indicate about the range of the varia- 
 tions in the size of the grains of sands that are 
 best suited to practical uses. 
 
 MECHANICAL ANALYSIS OF SANDS. 
 
 
 Effective 
 Size 10 
 per Cent 
 Finer 
 than 
 
 Uni- 
 formity 
 Coeffi- 
 cient. 
 
 Filter-tank 
 (i tt 
 
 (i 11 
 
 Sewage-filte 
 < < 
 
 
 Water-filter, 
 
 
 tt 
 
 No i Lawrence Mass 
 
 Millim. 
 .48 
 .18 
 .08 
 
 .10-. 24 
 
 .12 
 
 35-- 42 
 .25-. 30 
 .27 
 
 .29 
 
 .25-. 35 
 
 2.4 
 2.0 
 2.0 
 6-14 
 3-4 
 
 4-5 
 2.5-4-5 
 1.8 
 
 2.0 
 I.8-I.Q 
 
 
 " 2 " " 
 
 rs Gardner Mass 
 
 Marlborough Mass 
 
 South Framinghani Mass . 
 
 
 
 Southwalk, Vauxhall & Co., London, 
 
 Poughkeepsie N Y 
 
 
 * The lines were drawn by the author. 
 
DISPOSAL B Y INTERMITTENT FIL TKA TION. I I 5 
 
 The results of the mechanical analysis of the 
 sands of various filtering materials that are now 
 in use in several places for the filtration of sewage 
 or water, as taken from the 24th Annual Report 
 of the State Board of Health of Massachusetts, 
 are given on page 114 as a matter of general in- 
 terest. 
 
 " The amount of sewage which can be applied 
 in a single dose does not, however, give any in- 
 dication of the amount of sewage which can be 
 purified in a given time. With the fine materials 
 the sewage enters the sand slowly, and time must 
 be allowed for this slow process, and afterwards 
 for the water to drain out at the bottom, drawing 
 in at the same time fresh air from the top to 
 purify the next portion of sewage to be applied. 
 Two or three days must be allowed for this to 
 take place in sands as fine as Nos. 2 and 4, and 
 probably a longer time might be advantageous 
 under some conditions. With the coarser sands 
 the draining and renewal of air is more rapid, and 
 applications may follow each other at shorter in- 
 tervals without danger of exhausting the air. 
 The following table shows the doses whisji have 
 
SEWAGE DISPOSAL. 
 
 been proved to be adapted to the various ma- 
 terials under the most favorable conditions of 
 management, such as weekly raking of the sur- 
 face and absolute uniformity and regularity of the 
 application of sewage : 
 
 
 Diameter of 
 
 
 Size of 
 
 Dose. 
 
 Number 
 
 Average 
 Amount 
 
 Material. 
 
 Grain. 
 
 Millimeters. 
 10 per Cent 
 Finer than, 
 
 Depth of 
 Material. 
 
 Gallons 
 per 
 Acre. 
 
 Per Cent, 
 of Volume 
 of Filter. 
 
 of Doses 
 in one 
 Week. 
 
 Applied 
 Daily. 
 Gallons 
 per Acre. 
 
 No. 1 6 
 
 5-00 
 
 5 feet 
 
 2,800 
 
 O.I 7 
 
 500 
 
 200,000 
 
 i 
 
 .48 
 
 5 
 
 40,000 
 
 2-45 
 
 18 
 
 103,000 
 
 6 
 
 35 
 
 4 
 
 70,000 
 
 5-37 
 
 6 
 
 6o,OOO 
 
 9 
 
 17 
 
 5 
 
 I2O.OOO 
 
 7.36 
 
 6 
 
 103,000 
 
 2 
 
 .06 
 
 5 
 
 140,000 
 
 8.60 
 
 3 
 
 60,000 
 
 4 
 
 03 
 
 5 
 
 80,000 
 
 4.91 
 
 3 
 
 34,000 
 
 
 O2 
 
 
 o 
 
 
 
 o 
 
 
 
 
 
 
 
 
 " The smallness of the average amount applied 
 daily on No. 6 is in part due to its less depth (four 
 feet instead of five), and in part to the much smaller 
 volume of its pores, owing to its being a mixed 
 material containing particles having a wide range 
 in their diameters. As has been said, any practi- 
 cable dose on No. 5 is an overdose. It must be 
 borne in mind that the above figures are only 
 
DISPOSA L BY INTERMITTENT FIL TRA TION. 1 1 7 
 
 applicable to the comparatively clean materials, 
 under the most favorable conditions, and that so 
 large doses cannot be permanently applied with 
 good results without renewing of the surface ma- 
 terials." 
 
 In addition to the foregoing results, there are 
 others, both interesting and instructive, which the 
 author has summarized as follows : 
 
 i. Stratification and Effects of Horizontal Lay- 
 ers. "In all the filters filled during the earlier 
 years of the experimental station, the filtering 
 material was put in position by throwing it into 
 water. This method always results in some strati- 
 fication, the larger particles settling at once to 
 the bottom, while the finer grains remain longer 
 in suspension ; and in case the process of filling 
 is interrupted, even for a few minutes, the finer 
 particles settling out from a continuous layer of 
 much finer sand. 
 
 "We have thus found that with a coarse ma- 
 terial above a fine one in the same filter, there 
 is a chance of trouble from a clogging of the 
 surface of the fine material below the coarse ; and 
 
I 1 8 SEW A GE D ISP OSAL. 
 
 this is far worse than surface clogging, for the 
 latter can be completely remedied by distributing 
 the surface or by scraping. We have also found 
 that a fine sand supported by a coarse sand will 
 keep its lower layer saturated, and act as a water- 
 seal, allowing the passage of water but not of air, 
 and may in this way prevent the necessary circu- 
 lation of air and reduce the action of the filter 
 to a mere straining. Thus the possibility exists 
 that different materials which by themselves may 
 be suitable for the purification of sewage by inter- 
 mittent filtration may be so combined in a filter 
 that oxidation is rendered imperfect or impos- 
 sible." 
 
 " The above examples are perhaps extreme 
 cases. With less marked differences in the sand 
 grains, or with gradual instead abrupt transition 
 from coarse to fine, the causes of failure might 
 be reduced or even eliminated. In the many 
 cases where the fields available for sewage filtra- 
 tion contain layers of various materials, the differ- 
 ent sands must be separately studied, in order to 
 determine the probable action of existing combi- 
 
DISPOSAL B Y INTERMITTENT FIL TRA TION. 1 1 9 
 
 nations; and, in case the natural conditions are 
 unfavorable, changes may be made which will 
 improve the action of the filter." 
 
 2. Effect of Snow and Frost. il The two essen- 
 tial conditions to the passage of sewage through 
 the filters in winter are that sewage shall never be 
 put into snow, and that the filtering material shall 
 be open enough to absorb its dose rapidly." 
 
 "At Gardner, Massachusetts, with only a limited 
 filtration area, and with its sewage chilled nearly 
 or quite to the freezing-point before reaching the 
 beds, and of course, at times put directly into 
 snow, the filters have become badly frozen and 
 have refused to perform their work. At Fra- 
 mingham and Marlborough, with warmer sewage, 
 the results have been more favorable ; the beds 
 have regularly taken all the sewage and have 
 yielded well-purified effluents. A few beds at 
 Marlborough have indeed become frozen and 
 disabled ; but with the ample area provided, the 
 loss of a couple of beds is not serious : they can 
 be allowed to wait for a thaw, while other beds 
 continue to do the work." 
 
I2O SEWAGE DISPOSAL. 
 
 " The results at Framingham and Marlborough 
 (Massachusetts) demonstrate that with a suffi- 
 cient use of porous material and with not too 
 cold sewage intermittent filtration can be success- 
 fully carried on in very severe winter weather, 
 although with less complete purification of the 
 sewage than at other times. With colder sewage, 
 however, and only limited area, the problem be- 
 comes very difficult, and the present data are 
 inadequate for satisfactory discussion." 
 
 3. Permanency of Filters. "Of the nitrogen 
 stored in the filters more than 98 per cent, is in 
 the form of insoluble albuminoid ammonia, so 
 that it would seem that the insoluble organic 
 matters are mainly responsible for the clogging 
 of the filter." 
 
 " The constancy of the percentages of storage 
 of insoluble nitrogenous matters is remarkable. 
 Taking the final results, the highest are not twice 
 as great as the lowest, and with seven filters out 
 of nine the percentages are between 66 and 80. 
 This can only be interpreted as showing that 
 there are substances in sewage so stable as to 
 
DISPOSA L BY INTERMITTENT FIL TRA TION. 1 2 1 
 
 resist, for a very long time at least, the oxidizing 
 action of the filters. 
 
 "We have not as yet obtained a permanent 
 condition of equilibrium with no further increase 
 in storage. On the contrary, the organic matters 
 have been steadily increasing, and at a rate ap- 
 proximately equal to 70 per cent, of the insoluble 
 matters applied. This accumulation has now 
 proceeded so far in some of our filters as to 
 seriously cripple them." 
 
 4. Clogging of Sand. " Our present knowl- 
 edge in regard to the conditions of clogging may 
 be summarized as follows : 
 
 a. " Other conditions being the same, the clog- 
 ging of a filter is proportional to the amount of 
 sludge carried by the applied sewage." 
 
 b. " Other conditions being the same, a larger 
 proportion of the sludge of the applied sewage 
 is stored at a high rate of filtration than at a 
 lower rate." 
 
 c. " The same quantity of matter stored causes 
 more trouble at high rates than at lower rates." 
 
 d. " The condition in which the clogged sand 
 
122 SEWAGE DISPOSAL. 
 
 exists on the filter has an important influence 
 upon the results obtained, and it is not clear that 
 the most favorable conditions have as yet been 
 secured." 
 
 e. " The clogged sand by itself becomes slowly 
 oxidized, but to what extent is as yet uncertain." 
 
 f. " The clogged sand under some conditions 
 may serve as a filtering material with good re- 
 sults." 
 
 " While it must be admitted that the subject is 
 by no means exhausted, the indications point to 
 a much slower clogging of actual filters, run at 
 moderate rates, than has been observed in the ex- 
 perimental filters pushed to their full capacity." 
 
 5. Acid Sewage. " The effect of acid is quite 
 similar to the effect of frost ; both tend to pre- 
 vent nitrification, and check, but do not entirely 
 prevent, the oxidation of organic matter." 
 
 " If the sewage is only occasionally acid, or if 
 the filtering material contains available base, the 
 acid will not injuriously affect the result. If, 
 however, the filtering material contains no lime, 
 and the sewage is so constantly and strongly acid 
 
DISPOSAL BY INTERMITTENT FILTRATION. 123 
 
 as to interfere with the results, a little limestone, 
 put upon the surface, or dug into the upper layers 
 of the filter, will completely overcome the effect 
 of the acid." 
 
 6. Systematic Scraping. " The filters used for 
 the disposal of sewage at Gardner, Mass., are sys- 
 tematically scraped, with a two-day interval of 
 applying sewage, and apparently with excellent 
 results." 
 
 7. Area of Filters. " It is evident that filters 
 should be provided for the maximum rather than 
 for the average sewage-flow ; but, on the other 
 hand, a filter in good condition should be able to 
 take much more sewage for a single day than it 
 would be safe to apply every day, and so the in- 
 creased size of filters would not need to be as 
 great as the ratio of the maximum to the average 
 daily flow. 
 
 " In severe winter weather, under ordinary con- 
 ditions, it seems inevitable that filters will occa- 
 sionally become disabled by frost ; and, although 
 such a filter can be put in operation by the free 
 use of a pick, making holes to the porous ma- 
 
124 SEWAGE DISPOSAL. 
 
 terial, it would be much cheaper and more satis- 
 factory in every way to have enough area so that 
 in such cases the frozen bed could be allowed to 
 remain unused until the next thaw. 
 
 " Beds will also at times become clogged, and 
 require to be treated in someway before applying 
 more sewage ; and as it may not be always con- 
 venient to attend to such matters at short notice, 
 it is desirable to have extra area, which will allow 
 the treatment to be undertaken at a convenient 
 time. From every point of view, then, and en- 
 tirely aside from the important question of a fac- 
 tor of safety, it seems desirable, even necessary, 
 to have the filtering area larger than is indicated 
 by the Lawrence experiments. These experi- 
 ments should be taken to indicate the theoretical 
 rather than the practical limit of the process. 
 They afford a convenient, and, when used in the 
 proper way, a reliable basis for estimates ; but 
 the figures should not be used to represent the 
 possible average yearly work of a large plant." 
 
 Probably no experiments that have ever been 
 made to determine the principles involved in 
 
DISPOSA L BY IN TERM I T TEN T FIL TRA TION. I 2 5 
 
 purification of polluted water by intermittent fil- 
 tration have been so comprehensive in their scope 
 or so carefully or fully recorded as have the ex- 
 periments made by the eminent scientists and 
 specialists under the direction of the State Board 
 of Health of Massachusetts. The results are 
 worthy of the skill, time, and expense bestowed 
 upon them ; for they are fruitful in matters of 
 general interest and importance. While, as the 
 Board of Health states, the experiments indi- 
 cate the processes and results of natural puri- 
 fication of polluted water under the most favor- 
 able conditions, yet they have developed much 
 information that is of practical utility, and have 
 demonstrated that Nature has provided all that 
 is required for the complete purification of waters 
 containing organic impurity, and that to render 
 this processof Nature available in sewage disposal 
 it is necessary to observe the varying mechanical 
 and chemical conditions of both soil and sewage, 
 and to avoid restricting the process by artificial 
 conditions or burdening it with more work than 
 can be accomplished. 
 
126 SEWAGE DISPOSAL. 
 
 It is now interesting to know to what extent 
 the results as attained by the careful and elabo- 
 rate experiments at the Lawrence experimental 
 station may be verified in the practical application 
 of the purification of town sewage by intermit- 
 tent filtration. Of such an application there are 
 three good examples in the present practices of 
 the towns of Framingham, Marl borough, and 
 Gardner, Massachusetts. 
 
 At Framingham is is said that, " owing to 
 the height of the land above an adjacent brook 
 and the porosity of the material, only a limited 
 amount of underdrainage was found to be neces- 
 sary ; and most of the effluent, instead of coming 
 out of the underdrains, passes for a long distance 
 through the ground, and appears in the form of 
 springs at the edge of the low land near the 
 brook. That portion of the effluent which comes 
 out through the underdrains is very well purified, 
 particularly in summer, while that which passes a 
 long distance through the ground and comes out 
 at the springs is completely purified." * 
 
 *See Report Mass. State Board of Health for 1892. 
 
DISPOSAL BY INTERMITTENT FILTRATION. 127 
 
 " The results obtained at Framingham in the 
 disposal of sewage have been very satisfactory, in- 
 deed, as all of the sewage has been filtered with- 
 out causing offence in the neighborhood, and 
 without injuring the small brook into which the 
 effluent flows." 
 
 "The water from the underdrains as dipped 
 up and examined at the sewage-field is perfectly 
 clear, colorless, and odorless, and furnishes no 
 indication of being other than good spring-water ; 
 When, however, it is subjected to the severer tests 
 of the laboratory, and the water is shaken in a 
 half-filled gallon-bottle, after it has stood a day, a 
 musty and even an offensive odor is sometimes 
 noticed. The analyses show that 98 per cent, of 
 the organic matter, as represented by albuminoid 
 ammonia, is removed from the sewage when the 
 effluent leaves the underdrains, and they also show 
 a reduction of 91 per cent, in the amount of free 
 ammonia." 
 
 At Marlborough a portion of the suspended 
 matter of the sewage is separated by means of 
 screens and separating-tanks before the sewage 
 
128 SEWAGE DISPOSAL. 
 
 passes onto the filter-beds. " The sand is some- 
 what finer than at Framingham . . . and it was 
 found necessary to underdrain the land. . . . The 
 filter-beds were prepared for use by the removal 
 of very nearly all of the loam." . . . "The results 
 obtained at Marlborough have on the whole been 
 satisfactory, as the sewage has been purified to 
 the extent of removing 95.5 per cent, of the or- 
 ganic matter as represented by the albuminoid 
 ammonia ; and it has been shown that it is fc isi- 
 ble to purify the sewage in this way without 
 causing offence in the neighborhood. There has 
 been, however, at times a strong odor from the 
 sludge-beds when the sludge was allowed to re- 
 main upon them a long time, and even when the 
 sludge-tanks are emptied twice a month upon 
 the beds, and the sludge is removed as soon as it 
 dries, there is considerable odor while it remains 
 on the beds."* 
 
 At Gardner " the beds had to be almost 
 wholly artificial, and their total area was neces- 
 
 * See Report Mass. State Board of Health for 1892. 
 
DISPOSAL BY INTERMITTENT FILTRATION. 1 29 
 
 sarily quite small. The material is coarse sand, 
 and the beds are very thoroughly underdrained 
 by lines of tiles laid twenty feet apart and from 
 four to five feet beneath the surface, Although 
 the area of the bed is limited, it has been found 
 feasible to dispose of all of the sewage by filtra- 
 tion in summer and obtain a good effluent, if the 
 sediment is frequently raked in or removed from 
 the surface of the beds ; but in the cold winter 
 weather, when this sediment cannot be removed, 
 the beds have become partially clogged, and some 
 of the sewage has run over into the brook. . . . 
 The analyses show that 89 percent, of the organic 
 matter as represented by the albuminoid ammo- 
 nia, is removed from the sewage by filtration." 
 
 The results obtained in these towns, Framing- 
 ham, Marlborough, and Gardner, which have a 
 population respectively of 9,239, 13,805, and 8,424 
 inhabitants, demonstrate very clearly the practi- 
 cability of this method of sewage disposal, when 
 applied to small- and medium-sized towns ; and 
 where there are available a sandy, coarse-grained 
 and well-drained soil and proper facilities for the 
 
130 SEWAGE DISPOSAL. 
 
 uniform distribution of the sewage over the filter- 
 beds and for keeping the pores of the sand from 
 becoming seriously clogged. Moreover, these 
 practical examples of intermittent filtration of 
 sewage demonstrate that the slower the rate of 
 filtration and the longer the course taken by the 
 sewage in transit through the soils the more 
 effectively is purification accomplished, and 
 therefore that time and distance are important 
 elements of successful filtration. 
 
 With respect to the application of this method 
 of sewage disposal throughout the country, it 
 does not appear that the application can be other 
 than sectional, unless the soil conditions in many 
 localities be artificially made favorable. But 
 even in those localities where the method may be 
 usefully applied, there appears no conclusive war- 
 want in the results of the investigations as thus 
 far made public that crude sewage can be applied, 
 even to land of the most favorable mechanical 
 mixture, with a continuous and an equal degree 
 of success from year to year, without first remov- 
 ing the suspended and insoluble solids of sewage 
 
DISPOSAL B Y INTERMITTENT FIL TRA TION. 1 3 I 
 
 which constitute about 50 per cent, of the total 
 organic impurity, and which are quite likly to 
 clog the soil, and to thus impair its filtering and 
 purifying capacity. As has been shown, the con- 
 dition of the experimental filters of Lawrence, 
 Massachusetts, indicate a steady accumulation of 
 the organic matter of sewage at the rate of 70 
 per cent, of the insoluble matter, and that this 
 accumulation has seriously crippled most of the 
 filters. Therefore it follows that clogging of the 
 sands of filter-beds is in practice an element of 
 danger when sewage is applied to the land in its 
 crude condition. Admitting, however, that the 
 rate of filtration in these experiments has been 
 fully up to the purifying capacity of the severally- 
 graded sands, and that the clogging of the sands 
 of the filters was consequently greater than it 
 would have been had the rate of filtration been 
 considerably less than the purifying capacities of 
 the filters, yet whatever be the rate of filtration 
 it is apparent that there is a continuous process 
 of clogging within the upper layers of a filter. 
 However, there may be a rate of application of 
 
132 SEWAGE DISPOSAL. 
 
 sewage to sand-filters, whereby an equilibrium of 
 the conditions in a filter may become established, 
 as when the oxidation of the accumulating in- 
 soluble organic matter within the filter by the air 
 and water becomes equal to the rate of clogging ; 
 but this point of balance among the natural pro- 
 cesses at work in a filter does not seem to have 
 been determined. While from a scientific stand- 
 point it may be advisable to determine as nearly 
 as practicable this point of balance, and may be 
 considered the part of judicious foresight to so re- 
 strict the application of sewage to filtering-areas 
 that the limits of safety with respect to clogging 
 be not disregarded, yet from other standpoints 
 the rate of filtration so restricted may be. imprac- 
 ticable, as when in the enforcement of measures 
 of economy in the management of municipal 
 affairs, the authorities controlling expenditures 
 favor the utilization of no greater acreage of land 
 than will admit at the present time of a passably 
 purified effluent. The inevitable and progressive 
 clogging of the land that will follow such a disre- 
 gard of the equilibrium of the process of Nature 
 
DJSPOSA L BY IN TERM IT TEN T FIL TRA TION. 1 3 3 
 
 will sooner or later necessitate the extension of 
 the filtering-area or a frequent scraping and re- 
 moving of the surface layers of the filter-beds. 
 But for extensions which are due to a diminution 
 of the filtering capacities of the soils rather than 
 to the increase of the volume of sewage, and for 
 expenses resulting from the removal of clogged 
 sands, the public, who judge largely by results, 
 are very liable to attach reasons derogatory of 
 this process of sewage disposal rather than of the 
 method employed in applying the sew r age to the 
 land or of the proportionment of volume and 
 acreage. On this line of reasoning it would 
 seem, therefore, that to insure a successful appli- 
 cation of sewage to land by this method of sew- 
 age disposal, it would be advisable either to com- 
 bine intermittent filtration with the growing of 
 crops upon the filtering-area, or to precede it by 
 the removal of the insoluble matter from the 
 sewage. For, on the one hand, the growing of 
 crops would favor an extended distribution of 
 the sewage upon the land and the revenues ac- 
 cruing from the sale of the crops would in a 
 
134 SEWAGE DISPOSAL. 
 
 measure offset the annual expenditures necessary 
 to maintain and operate the additional land re- 
 quired as a preventive of clogging; and, on the 
 other hand, the insoluble portion of the organic 
 impurity of sewage, after being separated from the 
 water, could be so disposed of as to cause little 
 or no trouble and offence, and the strained or 
 settled sewage could then be safely applied to the 
 filtering-area in volumes quite equal to the puri- 
 fying capacities of the sand. 
 
 This view may seem somewhat speculative be- 
 cause of the brief experience in sewage disposal 
 of the cities and towns of this country ; but there 
 is much evidence in the results of experiments 
 as thus far made public, and in the results of sew- 
 age disposal by land in this country, to admit of 
 and support such a speculation. Moreover, this 
 view is further supported by the results of the- 
 trials to filter the water from sediment-bearing 
 rivers for public use, which results indicate that 
 water from such sources to be successfully fil- 
 tered at a rate to render filtration commercially 
 practicable should be preceded by sedimentation. 
 
DISPOSAL BY INTERMITTENT FILTRATION. 135 
 
 It is apparent that in the purification of crude 
 sewage by intermittent filtration, as in that by 
 irrigation, the sanitary and commercial interests 
 are somewhat at variance ; for the former requires 
 a rigid adherence to such methods as will insure 
 by natural processes a thorough purification of 
 sewage, while the latter for purposes of retrench- 
 ment or economy seeks a minimum of expendi- 
 ture upon land and upon the manipulation of 
 sewage. There is urged, on the one hand, a 
 slow rate of filtration and a wide distribution of 
 sewage, and, on the other hand, a rapid filtra- 
 tion through porous ground of as small superfi- 
 cial area as possible. 
 
 To what extent the opposing elements of these 
 two aspects of sewage disposal may be harmo- 
 nized will depend very much upon the advantage 
 that is taken of local conditions and sentiments, 
 and upon the inclination of the management of 
 a filtering area towards the attainment of good 
 sanitary results. But for guidance in these par- 
 ticulars there can be no specific rules or regula- 
 lations : they are not matters to be successfully 
 
136 SEWAGE DISPOSAL. 
 
 treated of in text-books ; and the success that 
 may follow the application of this method of 
 sewage disposal in any instance will depend quite 
 as much upon the judgment displayed in harmo- 
 nizing the involved natural principles and the 
 results of experiment and experience with the 
 special conditions of the locality in question, as it 
 will upon the simple applications of principles 
 and results as they may be found arranged and 
 recorded in books of reference. 
 
 It would seem difficult indeed to harmonize 
 the sanitary and commercial aspects of sewage 
 disposal by intermittent filtration in a section of 
 country where the prevailing characteristic of 
 surface soils is that of fine grain and close texture, 
 as is true of a very large part of the central and 
 southern portion of the United States ; for this 
 method of sewage disposal in these localities is 
 not only naturally inapplicable but also quite in- 
 admissible, except by incurring a heavy expense 
 in transporting gravel and sand and of construct- 
 ing artificial filter-beds, together with such ac- 
 cessories as may be necessary to remove insoluble 
 
DISPOSAL BY INTERMITTENT FILTRATION. 137 
 
 matter from sewage before filtering it. In fact, 
 it is not very probable that in such localities 
 many attempts will be made to harmonize these 
 aspects, as they relate to intermittent filtration ; 
 for there will be found other methods of disposal 
 more in consonance with the sectional and local 
 peculiarities that can be utilized whenever the 
 treatment of sewage becomes necessary. 
 
138 SEWAGE DISPOSAL. 
 
 CHAPTER VI. 
 
 PURIFICATION OF SEWAGE BY CHEMICAL PRE- 
 CIPITATION. 
 
 THE application of a process of chemical pre- 
 cipitation to the purification of sewage is said 
 to date back more than a century ; and during 
 the period from the first application of this pro- 
 cess to the present time there have been hun- 
 dreds of patents taken out for the purpose of 
 chemically purifying sewage. 
 
 Either the patentees or their associates by 
 enthusiastically offering large prospective returns 
 from the sale of the precipitants from sewage 
 induced organized private capital to invest in 
 these patented processes and in the plants and 
 equipments necessary to carry them into effect ; 
 but these attempts, like the attempts to utilize the 
 manurial properties of sewage by the irrigation 
 
PURIFICATION BY CHEMICAL PRECIPITATION. 139 
 
 of growing crops, have generally proved abortive 
 commercial ventures. 
 
 The commercial unproductiveness of such enter- 
 prises has probably been largely due to the im- 
 practicability of attaining in practice the favorable 
 results that had been predicted as a consequence of 
 investigations and experiments in the laboratory, 
 and has perhaps been more thoroughly demon- 
 strated in England than elsewhere ; for there any 
 efforts to mechanically dispose of sewage were 
 largely directed to the utilization of its manurial 
 elements, and methods having this end in view 
 were given the preference in application. 
 
 Of all the processes that have been tried there 
 are only a few that are practicable, and these few 
 nearly all involve the use of lime, alum, some 
 salt of iron, or a combination of two or more of 
 these chemical compounds. In the eight or more 
 cities in this country where the sewage is purified 
 by chemical precipitation, nearly all use lime and 
 either alum or a salt of iron. 
 
 The amount of chemicals necessary to be used 
 in practice depends very much upon the chemical 
 
 jv,^v^5s 
 
 *r 
 
SEWAGE DISPOSAL. 
 
 characteristics of the sewage. There are instances 
 where it is necessary to vary during each day the 
 amount of chemicals that may be necessary for 
 precipitation, because of the varying acidity of 
 the sewage produced by occasional discharges of 
 acids from manufactories. 
 
 The experiments that have been made at the 
 Experimental Station at Lawrence, Mass., in 
 precipitating the solids from sewage have given 
 the following results : 
 
 i. With respect to the amount and cost of 
 chemicals : 
 
 " The experiments indicate that a certain defi- 
 nite amount of lime gives as good or a better 
 result than either more or less, and that in gen- 
 eral the more copperas, ferric sulphate, or alum 
 used the better the result ; and that ferric sul- 
 phate and alum usually require no lime for com- 
 plete precipitation, while with copperas a definite 
 amount of lime must be used." 
 
 It was determined that about 1800 pounds of 
 lime per one million gallons gave the best results, 
 and cost annually about 30 cents per inhabitant. 
 
PURIFICATION BY CHEMICAL PRECIPITATION. 14! 
 
 Of the other chemicals for the same annual cost 
 
 per inhabitant it was found to take per 1,000,000 
 
 gallons : 
 
 1000 pounds of copperas, and 700 pounds of lime. 
 
 270 pounds of ferric sulphate. 
 
 650 pounds of alum. 
 
 2. With respect to the comparative advantages 
 of the different chemicals : 
 
 " The lime process has little to recommend it. 
 Owing to the large amount of lime-water re- 
 quired, and the difficulty of accurately adjusting 
 the lime to the sewage, a very close supervision 
 would be acquired to obtain a good result, and 
 even then the result is inferior to that obtained 
 in other ways. 
 
 " Precipitation by copperas is also somewhat 
 complicated, owing to the necessity of getting 
 the right amount of lime mixed with the sewage 
 before adding the copperas. When this is done 
 a good res,ult is obtained." 
 
 "With more than one half a ton per million 
 gallons, the improvement does not compare with 
 the increased cost." 
 
H 2 SEWAGE DISPOSAL. 
 
 " Ferric sulphate and alum have the advan- 
 tage over both lime and copperas, that their addi- 
 tion in concentrated solution can be accurately 
 controlled ; and the success of the operation does 
 not depend upon the accurate adjustment of lime 
 or any chemical to the sewage. 
 
 "The results with ferric sulphate have been, 
 on the whole, more satisfactory than those with 
 alum. This seems to be due in part to the 
 greater rapidity with which precipitation takes 
 place, and in part to the greater weight of the 
 precipitate. It is probable, from the greater ease 
 with which ferric sulphate is precipitated, that it 
 would give a good result with a sewage that was 
 not sufficiently alkaline to precipatealum at once. 
 
 " It is quite possible that the same process 
 would not give equally good results upon all 
 kinds of sewage. For this reason, and also- on 
 account of changes in the price * of the several 
 
 * At Lawrence, Mass., the cost of lime was $9 per ton; of copperas, 
 $10 per ton; of alum, $25 per ton. The cost in solution for alum was 
 9 cents per pound; for ferric oxide, 3 cents per pound; for copperas, 
 2 cents per pound; and for lime, f of a cent per pound. 
 
PURIFICATION BY CHEMICAL PRECIPITATION. 143 
 
 chemicals, it is impossible to say that one pre- 
 cipitant is universally better than another." 
 
 " Using equal values of the different precipi- 
 tants, 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 used together, while lime and alum eaeh 
 gave somewhat inferior effluents." 
 
 " When lime is used there is always so much 
 lime left in solution that it is doubtful if its use 
 would ever be found satisfactory except in case 
 of acid sewage." 
 
 3. With respect to the purity of the effluent 
 from the precipitation tanks : 
 
 " It is impossible to obtain effluents by chemi- 
 cal precipitation which will compare in organic 
 purity with those obtained by intermittent filtra- 
 tion through sand. 
 
 " It is, possible to remove from one-half to 
 two-thirds of the organic matter of sewage by 
 precipitation, with a proper amount of an iron 
 or aluminum salt; and it seems probable that, in 
 
144 SEWAGE DISPOSAL. 
 
 some cases at least, if the process is carried out 
 with the same care as is required in the purifi- 
 cation of sewage by intermittent filtration, a 
 result may be obtained which will effectually pre- 
 vent a public nuisance." 
 
 " A very large proportion of bacteria and of 
 theoffTer organisms is removed." 
 
 About all that can be expected of chemical 
 precipitation, when practised on a large scale, is 
 to remove the undissolved and suspended matter 
 in sewage, thereby clarifying and in a measure 
 deodorizing it. Very little, if any, of the dis- 
 solved organic matter is removed. Therefore, as 
 a purifying process, chemical precipitation cannot 
 rank high. 
 
 The expense of treating the sewage and of 
 disposing of the sludge has been found to vary 
 from fifty cents to one dollar per inhabitant per 
 annum. The expense depends very much upon 
 the character of the sewage, the facilities for 
 disposing of the sludge, the income that may 
 be derived from its sale, and the amount of seep 
 and storm-water that must be handled with the 
 
PURIFICATION BY CHEMICAL PRECIPITATION. 145 
 
 sewage. The value of the sludge is indeed low, 
 and usually there is little demand for it. As it 
 comes from the precipitation tank it contains 
 ninety per cent, or more of water, and in this 
 condition is almost unsalable. When pressed it 
 contains about fifty per cent, of moisture, and 
 may be salable as sludge-cake ; but even then 
 it is of low manurial value, and something to be 
 gotten rid of as quickly as possible to avoid 
 offense. It would not require a very shrewd 
 farmer to see that a little conservatism on his part 
 regarding the use of such compounds as a fertil- 
 izer, or even a refusal to buy it might very con- 
 sistently result in his being requested to remove 
 it for whatever use could be made of it. In fact, 
 the putrescible character of sludge and the neces- 
 sity for a continual production of it in disposing 
 of sewage by chemical precipitation, are condi- 
 tions that maintain a continuous supply of an 
 article for which there can be no commercial 
 demand, inasmuch as a prompt removal is obliga- 
 tory. This fact, together with the comparatively 
 low order of sludge as a fertilizer, should correct 
 
146 SEWAGE DISPOSAL. 
 
 any erroneous impression that in practice any 
 large and continuous revenue can be derived 
 from the sale of this article. 
 
 In small towns where this method of sewage 
 disposal may be in use, the sludge, being of a 
 small amount, can be readily disposed of by 
 digging it into the ground, or by giving it to the 
 farmers ; but in large towns, where the amount 
 is great, the removal must be accompanied with 
 expense to the city or town, and the method of 
 least expense is naturally the one to be chosen in 
 any specific case, whatever it may be. 
 
 The effluent from a chemical precipitation 
 works containing practically all the dissolved 
 organic matter of the untreated sewage is in a 
 putrescible state, and may under conditions of 
 high temperature or insufficient dilution putrefy 
 and again become offensive. This process, there- 
 fore, is one to be used in a guarded manner 
 where only a partial purification of sewage is 
 necessary, by removing the insoluble matter, and 
 where the effluent will not be exposed to condi- 
 tions promoting subsequent putrefactive changes. 
 
GENERAL DISCUSSION. 147 
 
 CHAPTER VII. 
 
 GENERAL DISCUSSION. 
 
 THE theory already referred to, that sewage 
 disposal should be one of sewage utilization, 
 because sewage contains the elements which 
 through the processes of Nature are requisite for 
 the support of vegetable life, might doubtless 
 have more application in practice were the con- 
 ditions governing the production and disposal of 
 sewage such that Nature could regulate both the 
 supply of sewage and the demand for it. But so 
 long as the demand is fixed entirely by Nature 
 and is subject to a seasonal fluctuation and re- 
 quires a wide distribution, and the supply is con- 
 trolled wholly by artificial conditions and is 
 practically constant and concentrated, there can 
 be no systematic and uninterrupted utilization of 
 sewage. 
 
148 SEWAGE DISPOSAL. 
 
 No matter what may be the intrinsic value of 
 the manurial constituents of sewage, so long as 
 the conditions affecting the supply and demand 
 can neither be controlled nor regulated, its com- 
 mercial value must remain very small, indeed so 
 small that sewage is much more likely to become 
 a source of expense than one of revenue to any 
 community having it to dispose of. 
 
 What becomes of sewage apparently concerns 
 communities very little, so long as it becomes 
 neither offensive nor dangerous to health. Re- 
 sults are what people look to ; and, aside from the 
 commercial bearings of sewage disposal, it mat- 
 ters not to them whether the process of disposal 
 be one of utilization, purification, or of simple 
 disappearance, so long as it occasions no danger 
 or annoyance. But to insure exemption of 
 offence from sewage, it is necessary to artificially 
 remove the decomposable matters from it, or to 
 surround it by such natural conditions as will 
 admit of and promote natural purification. In 
 a broad sense, therefore, the final object of any 
 method of sewage disposal is purification, involv- 
 
GENERAL DISCUSSION. 149 
 
 ing the removal, the destruction, or the wide dis- 
 tribution of the small percentage of putrescible 
 organic matter of sewage. In other words, a foul 
 and decomposing fluid must be transformed into 
 a clear and stable one, or so diluted with water 
 that natural processes of purification will either 
 prevent offensiveness or render it indiscernible. 
 
 Purification is a slow but progressive process, 
 requiring a considerable interval of time for its 
 accomplishment, and any interval of time less 
 than this will result in a proportionally less de- 
 gree of purification ; but the interest of commu- 
 nities can usually be sufficiently well subserved 
 by the attainment of such a degree of purifica- 
 tion as will prevent offence to the senses or as 
 will avoid danger to health through the medium 
 of drinking-water. The process has, therefore, 
 a twofold bearing, upon which bearings the topical 
 discussion of the preceding pages has aimed to 
 throw some light. However, in this discussion 
 no definite limits to the degree of purification 
 has been fixed, either as regards offences to the 
 senses or as to the pollution of water supplies ; 
 
150 SEWAGE DISPOSAL. 
 
 indeed, it is quite impracticable to do so ; for 
 any standard of purity, to be practically appli- 
 cable, must be elastic enough to suit a variety of 
 localities and conditions, and must consequently 
 become indefinable except in particular in- 
 stances. 
 
 Oxygen, derived largely from the atmosphere, 
 is the promoter and supporter of purification ; 
 while both water and earth are, in a great meas- 
 ure, the medium through which the process takes 
 place. In water organic matter becomes dis- 
 sipated by dilution and oxidation. On land it 
 disappears by evaporation, oxidation, and absorp- 
 tion ; but there is no evidence to show that the 
 process of purification is any more complete in 
 the one medium than in the other. 
 
 The ability of land to purify organically im- 
 pure water is definitely proven. 
 
 Nature furnishes pure spring or ground waters 
 from rain-water that has previously absorbed 
 from the air and from the surface of the ground 
 much putrescible organic impurity, and thus 
 offers direct evidence that a wide distribution 
 
GENERAL DISCUSSION. I$I 
 
 and a slow rate of filtration of impure water can 
 affect complete purification. This evidence is 
 the origin of the conception of intermittent 
 filtration as a process of purification at least 
 with unfailing supplies of oxygen and life and 
 with unlimited time and distance for its comple- 
 tion. 
 
 But in Nature the removal of this impurity 
 in water is no more a question of utilization by 
 growing vegetation than it is that of purification 
 by filtration through the ground. Therefore, in 
 practice, in imitation of the process of Nature, 
 the disposal of sewage upon land becomes a ques- 
 tion not of utilization or of irrigation or of inter- 
 mittent filtration, but rather one of land disposal 
 for the purpose of purification, embodying all 
 these special methods of treatment. By labora- 
 tory experiments and experience on a large scale 
 in filtering sewage through porous earth, it has 
 been demonstrated that purification can be ac- 
 complished by artificial filtration ; that in artifi- 
 cial filtration there is danger of the pores of the 
 ground becoming clogged by the insoluble mat- 
 
IS 2 SEWAGE DISPOSAL. 
 
 ter in sewage, thus more or less completely 
 arresting the process of purification ; that such 
 fine soils as clay, loam, and peat do not admit 
 of successful filtration, because of capillary at- 
 traction ; that snow and cold hinder or arrest it ; 
 and that still other contingencies may combine to 
 prevent successful purification by land at high 
 rates of filtration. 
 
 We know that capillary attraction must seri- 
 ously affect filtration. Nearly all soils have at 
 least 30 percent of their volume as voids; but 
 this or any other percentage of voids or air-space 
 in any ground is no index of its filtering capac- 
 ity. For instance, the air-space of a mixture of 
 coarse sand and gravel is composed of a com- 
 paratively small number of large voids, but the 
 air-space may be about the same percentage of 
 the total volume of the mixture, as is that of. a 
 fine loam or garden soil wherein the air-space is 
 composed of a large number of very small voids. 
 Though both of these materials may hold the 
 same amount of water when saturated, yet when 
 free to drain the sand and gravel will loose from 
 
GENERAL DISCUSSION. 1 53 
 
 75 to 80 per cent of its water, while the soil 
 will loose little or none, and in any event at a 
 slow rate of percolation. The water remains in 
 the soil because of capillary attraction, which is 
 greater in this instance than is the attraction 
 of gravity drawing the water downwards. The 
 sand and gravel, by careful applications of sew- 
 age, may be made to purify sewage, but at a rate 
 of filtration far less than the ability of such a 
 filter to drain ; on the other hand, the fineness of 
 the voids in soil renders such a material reten- 
 tive of water and consequently valueless for 
 filtering purposes. To underdrain such soil may 
 in a measure increase its filtering capacity by 
 promoting a freer and more direct circulation 
 through the pores of the filtering material from 
 the outer air to the drain ; but the drains would 
 not be at all likely to free the soil of water. 
 In fact, from such a soil the moisture is largely 
 removed by evaporation from the surface layers 
 these layers, as fast as deprived of water by 
 evaporation, becoming supplied by capillarity 
 from layers at greater depths ; that is, a reten- 
 
154 SEWAGE DISPOSAL. 
 
 tive soil is drained of its water by evaporation 
 from the surface of the ground far more than by 
 percolation through it. Were this not a pro- 
 vision of Nature to support vegetation, a fine and 
 retentive soil would become quite as unproductive 
 as porous and well-drained sands. This process 
 is the one that contributes materially to the pro- 
 ductiveness of a great part of our Western 
 States, where fine soils nourish vegetation during 
 droughts by drawing water from the subsoils by 
 capillarity a process of natural pumping, just 
 as a sponge or linen towel will draw water to a 
 considerable height until saturated. Although 
 retentive soil admits of some filtration, yet the 
 amount is so small that the use of it for sew- 
 age-disposal purposes requires the sewage to be 
 widely distributed and the land to be cropped, 
 for the greater portion of the moisture must be 
 removed by absorption of plants and by evapora- 
 tion. 
 
 The more porous the soil the less capillary 
 attraction affects filtration ; for this reason sandy 
 
GENERAL DISCUSSION. 155 
 
 land is capable of disposing of more sewage than 
 is loam land. 
 
 The extent to which snow and cold may affect 
 filtration is largely a question of geographical 
 location. 
 
 The clogging of the soil of disposal areas, in 
 view of the results of the experiments of the 
 Lawrence (Mass.) Experimental Station, as re- 
 corded in Chapter V, is to be apprehended ; and 
 it may result in the serious impairment of the 
 filtering capacity. These experiments indicate 
 that any land, whether it be loam, sand, or gravel, 
 if the amount of sewage applied but approximate 
 that amount which limits the original filtering 
 capacity of the material, will sooner or later be- 
 come impaired both as a filtering and a purifying 
 medium. 
 
 This condition of soil impairment may not be- 
 come prominently apparent for several years, but 
 it cannot be expected that land can receive the 
 insoluble matter of sewage day after day and 
 month after month, in large quantities, without 
 becoming gorged, as it were, by the accumula- 
 
156 SEWAGE DISPOSAL. 
 
 tions. Clogging seems inevitable as the result 
 of a continuous application of crude sewage. In 
 all probability it will become evident much ear- 
 lier in loam lands than in sand and gravel lands, 
 because the tendencies to economize in the 
 management of municipal affairs, as is frequently 
 apparent, may prevent a proper discrimination 
 between the filtering capacities of the two mate- 
 rials and the consequent utilization of less loam 
 land than is really necessary for the continuous 
 attainment of purification, and may result in such 
 an injudicious apportionment of area and vol- 
 ume of sewage as to speedily overtax the fine 
 soil. 
 
 Glancing back to the table on page 1 16 it will 
 be seen that the Lawrence (Mass.) experiments 
 indicate the purifying capacities of the various 
 materials experimented with to be from 200,000 
 to 34,000 gallons per acre per day, which amount 
 of sewage is the equivalent of about 3000 to 500 
 inhabitants per acre. But it should be remem- 
 bered that these experiments were conducted with 
 a view of determining maximum and theoretical 
 
GENERAL DISCUSSION. 157 
 
 values, and were the recipient of far more skilled 
 and careful attention than will ever prevail in 
 practical sewage disposal by land. Moreover, 
 many of the filters became clogged, and were 
 thereby seriously Gripped because of a continu- 
 ous storage of insoluble matter. The results of 
 these experiments with respect to the filtering 
 capacities of various materials, while instructive, 
 are not intended for application in practice with- 
 out much modification. As a matter of fact, 
 having in the majority of cases to take land in 
 its natural condition, without the opportunity 
 of either choosing the material or arranging it in 
 the best manner for filtration, and having usu- 
 ally to rely on unskilled labor to manage the dis- 
 posal areas, it is obvious that the amount of sew- 
 age to be applied should be very much less than 
 the theoretical amount. A reduction of one- 
 fourth to one fifth would usually be none too 
 much. 
 
 In England it was originally estimated that 
 by intermittent filtration one acre of land could 
 filter the sewage of 2000 inhabitants; this value 
 
158 SEWAGE DISPOSAL. 
 
 has since been reduced to 1000 inhabitants per 
 acre under most favorable conditions of filtering 
 material and management. 
 
 On the irrigation farm of Berlin, the decrease, 
 as stated on page 87, is from 250 to 75 or 50 in- 
 habitants per acre. It is seldom on any of the 
 irrigation farms of foreign countries that the pro- 
 portion exceeds 300 per acre. 
 
 Some sanitarians of this country assert that an 
 acre of good land without cropping should purify 
 the sewage of 1000 to 2000 people. While it is 
 to be hoped that such results may be attained, 
 and that the practice in this country may find 
 purification of sewage practicable at higher rates 
 of filtration than has prevailed in the practice of 
 foreign countries, yet such a conclusion does not 
 seem admissible in the light of such experiments 
 as have been made in this country. Such high 
 rates of filtration of crude sewage, with no more 
 skilled management than will ordinarily obtain, 
 would cause the ground to become clogged, un- 
 less it should be of a sandy nature in a country of 
 light rainfall, where the evaporation and oxidation 
 
GENERAL DISCUSSION. 159 
 
 of the insoluble substances arrested by the sand 
 would be rapid. 
 
 Moreover, there is no good sanitary reason, so 
 far as purification may be concerned, why the 
 cropping of disposal areas should be discounte- 
 nanced. To do so is neither in imitation of Nat- 
 ure nor in accord with those considerations of 
 economy which aim to reduce the cost of sewage 
 disposal by land through the returns in crops 
 from cultivated disposal-lands. In fact, the 
 tendency is rather to crop disposal land than 
 otherwise, as evidenced by the practice of Fra- 
 mingham, Mass., a town admirably located, as we 
 may judge, for the exclusive disposal of sewage 
 by intermittent filtration, which in 1892 raised 
 crops of various kinds of vegetables with such 
 satisfactory results as to repeat the experiment 
 with additional acreage in 1893. And it may be 
 quite safely predicted that the practice of sewage 
 disposal by land in this country will, in imitation 
 of the purifying process of nature, sooner or later, 
 favor the cropping of lands to any extent that 
 may be admissible in the interests of an econom- 
 
l6o SEWAGE DISPOSAL. 
 
 ical and sanitary management. In a very large 
 portion of the central and western United States, 
 the prevailing fine, loamy and clayey soils can 
 advantageously afford natural facilities for no 
 other method of land disposal of crude sewage 
 than that which would admit of a wide distribu- 
 tion of sewage coupled with the cropping of 
 lands. Here the admissible population to be 
 served per acre of land should, with due regard 
 to purification and to the avoidance of offence, 
 scarcely ever exceed 200 to 400 per acre, and 
 even a less number may be found advisable to 
 insure freedom from clogging. 
 
 At unseasonable times for cropping, land dis- 
 posal in almost any locality must, in the case of 
 porous soils, become one largely of intermittent 
 filtration or, in case of retentive and non-filtering 
 soils, one largely of deposit and evaporation, 
 wherein the sewage in flowing over the land 
 becomes clarified because of depositions of sus- 
 pended matter. 
 
 The proportions of population to the acre of 
 land, as generally given, is largely one of general 
 
GENERAL DISCUSSION. l6l 
 
 averages. But in practice the capacity of soils 
 for purposes of sewage disposal is in every in- 
 stance a question of specific amount rather than 
 one of general average, and as such the acreage 
 of land for any assumed number of population 
 should be based entirely upon a conformation of 
 the physical characteristics of the soils of available 
 land, with the special and local requirements of 
 the place. In other words, in sewage disposal 
 by land there is in every instance a specific 
 amount of work to be accomplished by natural 
 processes ; consequently, the amount of the work 
 should harmonize with the peculiar conditions of 
 the soil in the locality in question. Average 
 ratios of population and land, arbitrarily chosen, 
 are simply the average results of land disposal of 
 sewage in many or few places ; and, as such, can- 
 not become such a criterion for practice in spe- 
 cific instances as can the results of a purely 
 mehanical process. 
 
 Any practice of land disposal that burdens the 
 natural process at work in the removal of the 
 organic impurity of sewage impairs the filtering 
 
1 62 SEWAGE DISPOSAL. 
 
 and purifying capacity and ability of the land. 
 This can be obviated, either by so wide a distri- 
 bution of sewage over the land as to insure the 
 proper and effectual assistance of Nature in the 
 work, or by removing the insoluble matter from 
 sewage previous to applying it to land in inter- 
 mittent filtration. 
 
 By clarifying sewage before applying it to 
 land and by the use of sandy ground for filtering 
 purposes, the area of disposal land may be re- 
 duced to its smallest limit, cropping may be 
 avoided, and the theoretical filtering capacities 
 of land may be most nearly approximated. 
 
 The disposal of sewage into watercourses has 
 indeed been a most natural transition from the 
 disposal of excrement into the waste water from 
 habitations ; the only difference being that the 
 conditions affecting the removal of sewage. by 
 natural waters are fixed by Nature, while those 
 effecting the removal of excrement through arti- 
 ficial channels are wholly controllable and ad- 
 justable. But such a method of disposal involves 
 a process of purification quite as much as does 
 
GENERAL DISCUSSION. 163 
 
 land disposal. It became a custom both from 
 motives of economy and expediency of econ- 
 omy, because it utilizes a natural drain and a 
 natural vehicle for the removal of waste and of 
 products of decomposition ; and of expediency, 
 rather because it was thought proper and -desir- 
 able to remove sewage in this manner than be- 
 cause of motives of self-interest or of a disregard 
 for a neighbor's convenience. But this practice 
 of sewage disposal has been the occasion of 
 objection because of the offensiveness and mal- 
 odorousness of waters excessively charged with 
 sewage ; and, of condemnation, because of sup- 
 posed danger to health of water abstracted from 
 sources of supply previously polluted by sewage. 
 The cause of offence can be removed, as has been 
 shown in Chapter III, by restricting the amount 
 of sewage entering a given volume of water to 
 that which can be removed and purified by the 
 natural processes prevalent in normal waters. 
 
 The most significant element of sewage dis- 
 posal by water is the one that involves questions 
 affecting the purity of water supplies. There is 
 
164 SEWAGE DISPOSAL. 
 
 always a natural abhorrence to partaking of a 
 water supposed to be polluted with fecal matter. 
 Whatever may be the elements of danger to 
 health in a water thus contaminated, considera- 
 tions of self-respect and decency do not tolerate 
 its use as a public water supply. While a water 
 that at some time of its history has been polluted 
 with sewage may not be necessarily dangerous to 
 health, yet of a source of water supply so con- 
 taminated there are frequently good grounds for 
 a suspicion that the intervals of time and distance 
 between the point of pollution and the point of 
 abstraction may not have been sufficient to in- 
 sure complete purification. Merely prohibiting 
 the discharge of sewage into sources of public 
 water supplies cannot remove this suspicion of 
 danger, for other sources of pollutions, some of 
 which have been enumerated in another chapter, 
 and which are quite uncontrollable, are in many 
 instances of quite as grave consequence. 
 
 Inasmuch as the extent of the pollution of 
 surface-water can neither be wholly controlled 
 nor regulated, and since the provisions which, in 
 
GENERAL DISCUSSION. 165 
 
 the main, are sufficient to prevent any ill effects 
 coming from a surface-water that may have 
 received pollution from uncontrollable sources 
 can be made quite as effective in the majority 
 of cases of sewage pollution, it follows that one 
 of two things should be done by cities and towns 
 with regard to their water supplies, namely : that 
 they either derive their water supplies from un- 
 polluted sources or adopt such measure as shall 
 prevent contaminated water reaching the con- 
 sumers. One or the other of these courses is 
 always available ; and while the one that secures 
 a supply of water from an unpolluted source is 
 by far the more preferable from a sanitary stand- 
 point, still the other course can attain to a safe 
 degree of purity. 
 
 As though in anticipation of a general want, it 
 has been demonstrated by successive years of trial 
 that artificial filtration by natural processes can 
 be relied on to purify organically polluted water, 
 to remove infectiousness, and to be thoroughly 
 practicable. By its application to the purification 
 of water supplies, water can be purified immedi- 
 ately before consumption, and thus completely 
 
1 66 SEWAGE DISPOSAL. 
 
 avert not only the dangers but also the suspicions 
 of contamination. To partake of a water that 
 has been properly filtered, even though known 
 to ha-ve contained organic impurity previous to 
 filtration, need cause no shock to any considera- 
 tions of decency ; for the water has been actually 
 purified by a process that is entirely similar and 
 analogous to that one which renders spring and 
 ground waters pure and palatable, even though 
 they had previously been in contact with decom- 
 posing organic matter abounding almost every- 
 where upon the surface of the ground. In fact, 
 the conditions of a water purified by filtration 
 bears the same relation to the condition of the 
 water before filtration as does the refined condi- 
 tion of an article of diet or commerce as com- 
 pared with a former natural or crude condition ; 
 the impurities being simply associated with the 
 past history of the water or article, and the puri- 
 fied or refined condition of either being none the 
 worse for having originally contained them. But 
 it may be still contended that the proper way of 
 securing freedom from impurities in water is to 
 
GENERAL DISCUSSION. 1 67 
 
 prevent pollution ; but this measure, in a general 
 application, is wholly impracticable, and in partic- 
 ular application with regard to sewage it may 
 be further stated in contravention that to wholly 
 remove this cause of pollution would require a 
 change no less radical than one preventing the 
 introduction of excrement into the waste-water 
 from habitations. But sanitary science has found 
 no satisfactory substitute for the method in cur- 
 rent use of removing excrement by water-car- 
 riage ; and it is by no means ready to advocate 
 the exclusive application of sewage to land or 
 the disposing of it by any method wholly inde- 
 pendent of a discharge into natural waters. 
 There is yet no immediate probability of any 
 such radical change of present practices. 
 
 Doubtless the disposal of sewage in most in- 
 stances should have regulation : even legislative 
 enactments may in some case be necessary ; and 
 this is true of any method of disposal, whether it 
 be by land or by water. But legislation for this 
 purpose would in all probability be more effective 
 if directed to the regulation than to the prohibi- 
 
1 68 SEWAGE DISPOSAL. 
 
 tion of approved practices of sewage disposal, and 
 rather for specific than for general application ; 
 and, while it is seeking the purification of sewage 
 as a proper sanitary measure, it should recognize 
 that water disposal involves a process of purifica- 
 tion quite as much as does land or any of the other 
 methods of sewage disposal. 
 
 Furthermore, legislative enactments, intending 
 to regulate or to prohibit practices that may affect 
 the purity of drinking-water, would be even more 
 efficacious, more tangible, and more certainly 
 productive of good to communities, if exacting 
 greater care in the purification of water supplies 
 immediately before distribution to consumers, 
 than if solely directed to the prevention of the 
 ingress of organic matter and its accompaniments 
 into natural waters. 
 
 Failures and evil effects following the disposal 
 of sewage into water are, in all probability, the 
 result more of misapplied principles and tem- 
 porizing methods than of lack of natural powers 
 of self-purification in water. 
 
 Considering both land and water disposal of 
 
GENERAL DISCUSSION. 169 
 
 sewage in its broadest sense, there are manifestly 
 advantages and disadvantages to each. Either 
 method will fail to give good results, if the natural 
 conditions under which purification may progress 
 be not strictly observed for instance, land dis- 
 posal may result in a serious pollution of the 
 ground-waters, an impure effluent into water- 
 courses, and offensive odors upon and about a 
 disposal area ; and water disposal, in putrefactive 
 changes of organic matter in water overcharged 
 with sewage ; and both methods may then admit 
 infectiousness into water supplies. Moreover, 
 the insoluble part of sewage may deposit in bodies 
 of water or it may accumulate upon the surface or 
 within the pores of the ground because of insuffi- 
 cient distribution ; thus admitting, under favor- 
 able conditions, of putrefactive and objectionable 
 changes. The clogging of the ground will seri- 
 ously impair its filtering and purifying capacity. 
 
 A wide distribution of sewage, either through 
 water or upon land, will prevent offence from de- 
 posits. Such a distribution can usually be more 
 readily and economically attained in water than 
 
I/O SEWAGE DISPOSAL. 
 
 upon land ; for, in the one case, the currents and 
 general mobility of the water will generally and 
 widely distribute the sewage without mechanical 
 assistance, while in the other case the deposits 
 must be frequently raked and eventually mechani- 
 cally removed from the disposal area, or the land 
 allowed a considerable time of rest, in order that 
 natural disintegration of the insoluble matter of 
 sewage may take place. 
 
 In the event of the removal of the insoluble 
 portion of sewage becoming necessary before its 
 application to land or discharge into water, chemi- 
 cal precipitation may be used to effect clarifica- 
 tion. In a dual process of this character it is 
 quite probable that the disposal of the effluent 
 from the precipitation tanks may be less liable 
 to subsequent pollution, and may become more 
 quickly purified if applied to land, provided the 
 land be in every respect suitable for intermittent 
 filtration, than if thrown into water ; for the 
 chemicals remaining in the effluent have been 
 known to promote rapid decomposition after dis- 
 charge into water 
 
GENERAL DISCUSSION. IJl 
 
 In practice, chemical precipitation is largely 
 confined to the removal of insoluble matter ; and, 
 consequently, gives incomplete purification of 
 sewage. It therefore is more properly the pre- 
 liminary part of some dual process, the combined 
 effects of which is complete purification. 
 
 The present approved practices of sewage dis- 
 posal have now been discussed quite in detail, 
 somewhat generally and comparatively analyzed, 
 and the conditions and principles which are neces- 
 sary to the attainment of satisfactory results in 
 practical applications of these methods, have now 
 been outlined. In this discussion and analysis 
 no attempt has been made to bring out the con- 
 structive features, or to define the precise applica- 
 tions of any particular method of disposal. What- 
 ever bearing the views and discussions as herein 
 
 o 
 
 contained may have in specific instances in deter- 
 mining a proper mode of sewage disposal is wholly 
 a question of local issue. To advocate any method 
 of sewage disposal previous to a thorough know- 
 ledge of a locality is but to acknowledge a bias 
 its favor or to affirm of it a general applicability. 
 
I7 2 SEWAGE DISPOSAL. 
 
 Neither of these positions is a safe one to assume ; 
 for the most approved method of disposal will 
 invariably hinge upon its natural adaptability to 
 the conditions of the locality in question. 
 
 The author would sum up the discussion in a 
 few general conclusions : 
 
 1. Any acceptable method of sewage disposal 
 should aim to purify the sewage. Thus far, in 
 practice, sewage purification has been attained 
 only by natural processes. Water and land dis- 
 posal of sewage involves natural processes of puri- 
 fication, and either method properly employed 
 can afford practically complete purification. 
 
 2. The purification of sewage by water involves 
 dilution, settlement, and bacterial oxidation of 
 the organic impurity of sewage. 
 
 Crude sewage can usually be most expeditiously, 
 economically, and effectually disposed of by water. 
 All things considered, this method of disposal, 
 when available, is in all probability the best that 
 has yet been practised. Proper dilution and favor- 
 able temperature can prevent nuisances. 
 
 Sand filtration of polluted waters can remove 
 
GENERAL DISCUSSION. 1/3 
 
 any contained sewage impurity and infectious 
 matter. 
 
 There appears no occasion for general legisla- 
 tive enactments looking to the prohibition of 
 sewage disposal by water ; but measures regulat- 
 ing the method and extent of sewage disposal 
 by water may, in specific instances, be required. 
 
 3. Purification by land disposal involves both 
 irrigation and intermittent filtration, neither of 
 which methods is likely to be long employed to 
 the exclusion of the other. 
 
 Crude sewage applied to any land at a rate re- 
 motely approximating filtering capacity will in all 
 probability cause a clogging of the land and a con- 
 sequent reduction of its filtering and purifying ca- 
 pacity. Land so clogged must receive long rest 
 or must have the clogged earth removed. Land 
 disposal of crude sewage may be successful if 
 such sewage be given a very wide distribution 
 over the land. 
 
 Because of the many and variable disadvan- 
 tages which will attach to land disposal of sewage 
 in various parts of the country, it may be con- 
 
174 SEWAGE DISPOSAL. 
 
 sidered as available only in the event of a lack of 
 facilities for water disposal. 
 
 4. Chemical precipitation is but a semi-purify- 
 ing process, practically restricted in its workings 
 to the removal of the suspended matters of sew- 
 age. As a part of a dual process involving either 
 water or land disposal, it is valuable as prevent- 
 ing either the clogging of the land or deposits of 
 insoluble organic matter in bodies of water. The 
 sludge can have little or no commercial value, 
 chiefly because its presence, as a highly putres- 
 cible substance, causes an emergency which pre- 
 vents any regulation of supply and demand, by 
 which regulation only can any article either have 
 a commercial value or become salable. 
 
INDEX. 
 
 A 
 
 Acid sewage, 122, 123. 
 
 Air, purifying power of, 66-68, 
 
 Alum, chemical precipitation by, 141-143. 
 
 Analysis of water, chemical, 54, 55, 69. 
 
 Area of filters, 123. 
 
 B 
 
 Bacteria and purification of polluted water, 15-17, 54. 
 Bacteria, antagonism of, 60-63. 
 
 " in sewage, number of, 17. 
 
 " , nitrifying, 20-25, 54- 
 
 " , reducing, 21, 22, 54. 
 Berlin sewage farms, 87, 158. 
 Boston, sewage disposal of, 47-51. 
 
 C 
 
 Capillary attraction, 152-154. 
 
 Cesspools, 79, So. 
 
 Character of organic matter in sewage, 8, 13, 
 
 175 
 
176 INDEX. 
 
 Chemical analysis, 69. 
 
 Chemical changes of sewage, 17, 26, 54. 
 
 Chemical composition of sewage, 8-13. 
 
 Chemical precipitation, sewage purified by, 138-146, 170, 171. 
 
 Chicago, 111., water supply and sewage of, 34, 35, 39, 40 43. 
 
 Cholera, 59. 
 
 Clogging of sewage filters, 121-124, 130-134, 151, 152, 155-158. 
 
 Combined system of sewerage, 4, 5. 
 
 Commercial aspect of sewage irrigation and filtration, 84, 85, 95-97, 
 
 135, 136, 139, 147, 148. 
 Conclusions, general, 172-174. 
 Cost of chemicals, 140, 141. 
 
 " " treating sewage, 144. 
 Cropping of filtering areas, 133, 159, 160. 
 Crude sewage on land, effects of, 130, 135. 
 
 Decline of sanitary science, I, 2. 
 
 Development of modern sewerage, 2, 3, 4. 
 
 Defined, sewage, 7. 
 
 Deposits of organic matter, 44, 45. 
 
 Dilution of sewage, 32-41. 
 
 Dispersion of sewage, 45-53. 
 
 Disease, relation of sewage and, 57-67. 
 
 Disease-germs in water supplies, 69, 73-76. 
 
 Discharge of sewage into tide-water, 28-31. 
 
 Distribution of sewage on land, 134, 155, 157, 158, 160-162, 169. 
 
 E 
 
 England, sewage disposal in, 82-86, 105, 157. 
 
INDEX. 177 
 
 Farm, sewage, 87, 99-102, 158. 
 Fecal matter in sewage, amount of, 8, 9. 
 Filtering materials, 106-108, 113-117, 155-157. 
 Filtration denned, 103-109. 
 
 " , results of, 110-112. 
 
 " of sewage, 115-129, 151-153, 156, 158. 
 , slow, 130, 131, 135, 151. 
 
 " of water supplies, 63, 73, 75~77. 165-167. 
 Flushing of small streams, 80. 
 Framingham, Mass., filtration at, 119, 120, 124, 126, 129, 159. 
 
 Gardner, Mass., nitration at, 119, 120, 123, 126, 128, 129. 
 
 Gases from sewage, 57, 58. 
 
 General conclusions, 172-174. 
 
 General discussion of sewage disposal, 147-171. 
 
 H 
 
 Health and sewage, 87, 88, 149, 162-164. 
 
 I 
 
 Inland towns, sewage disposal of, 78-80. 
 
 Intermittent filtration, sewage disposal by, 103-137, 150, 151. 
 
 Introduction, iii, x. 
 
 Iron salts, sewage purification by, 141-143. 
 
 Irrigation, sewage disposal by, 82-102, 
 
INDEX. 
 
 Lakes, disposal of sewage in, 52, 53. 
 
 Land disposal of sewage, 151, 161, 168, 169. 
 
 Land for sewage disposal, 86, 87, 93, 98, 99, 156-158, 160, 161. 
 
 Lawrence, Mass., experiments in filtration at, 106-125, 140-144. 
 
 " " , filtration of water, 75, 76. 
 
 " " , water supply of, 61. 
 
 Legislation and sewage disposal, 167. 
 Lime in sewage disposal, cost of, 140. 
 London, sewage disposal of, 41, 42. 
 
 ' ' water supply and typhoid bacillus, 6l. 
 " filtration of, 73. 
 
 M 
 
 Manurial value of sewage, 82-84, 96, 148. 
 
 Marlborough, Mass., filtration of sewage at, 119, 120, 127-129, 
 
 Materials, filtering, 106-108, 113-117, 155, 157. 
 
 Mechanical composition of sand, 112-114. 
 
 Milwaukee, Wis., sewage disposal of, 35-37, 38, 43. 
 
 Mineral matter in sewage, 10-12. 
 
 Modern sanitation, first principle of, 3, 4. 
 
 N 
 
 Natural process of purification, 14-25, 26, 32, 33, 44, 45, 53-59, 78, 
 
 125, 147, 148, 159, 162, 165. 
 New York, sewage disposal of, 42. 
 Nitrates, 18, 21, 22, 55. 
 Nitrification of organic matter, 17-21, 55. 
 Nitrifying bacteria, 20-25, 54- 
 
INDEX. 179 
 
 Odors from sewage farms, 88, 89, 99. 
 Organic matter and bacteria, 15-56. 
 " , deposits of, 44, 45. 
 " in sewage, 8-13. 
 " " , nitrification of, 17-21, 55. 
 Organic vapors, effects of, 57, 58. 
 Oxidation of organic matter, 19-2 [, 55. 
 Oxygen in sewage, n. 
 " " water, 57, 150. 
 
 Permanency of sewage filters, 120, 121 
 Polluted water and bacteria, 15-17, 54. 
 Pollution of water, 69-71, 77, 78, 149, 164 
 
 " " subsoil waters, 89. 
 
 Prohibition of sewage disposal by dilution, 59, 63, 65, 73, 77, 167, 168. 
 Pullman, 111., sewage disposal of, 96. 
 
 Purification, natural process of, 14-25, 26, 32, 33, 44, 45, 53-59, 78. 
 Purification of sewage, 148-151, 156, 158. 
 
 " " by chemical precipitation, 138-146, 170, 171 
 
 " " , vital process of, 14-26. 
 
 Purification of water supplies, 66, 68, 72-74, 149, 151, 165-167. 
 Purified sewage, 10, u. 
 Putrefaction of organic matter, 13, 15, 17, 20, 42, 43, 45, 57. 
 
 Q 
 
 Questions affecting sewage disposal, 6. 
 
INDEX. 
 
 Results of filtration, 110-112. 
 
 Sands, mechanical composition of, 112-114. 
 
 Sand filtration, 73, 75-77. 
 
 Sanitary aspect of sewage disposal, 84, 85, 95-97, 135, 136, 147, 148. 
 
 Sanitary science, decline of, i, 2. 
 
 Sanitation, first principles of, 3, 4. 
 
 Self-purification of polluted water. 53-56, 59-61, 67, 68, 168. 
 
 Sewage, 7-13. 
 
 " , acid, 122, 123. 
 
 " and disease, relations of, 57-65, 67. 
 
 " , amount of organic matter in, 8, 9. 
 
 " , character of organic matter in, 8, 13. 
 
 " , chemical changes in, 17, 26, 54. 
 
 " , chemical composition of, 8-13. 
 
 " , defined, 7. 
 
 " dilution, 32, 33, 34-41. 
 
 " , dispersion of, 45-53. 
 
 " disposal by dilution, 27-81, 162, 163, 168, 169. 
 
 " chemical precipitation, 138-146, 170, 171. 
 
 " " " intermittent filtration, 103-137, 150, 151. 
 
 " " irrigation, 82-102. 
 
 " " , general discussion of, 147-174. 
 
 " in inland towns, 78, 79. 
 
 " " into lakes, 52, 53. 
 
 " " " streams, 28, 162. 
 
 " " " tide-water, 28-31, 37. 
 
 " " in United States, 90-98, 160. 
 
INDEX. l8l 
 
 Sewage farm, 99-102. 
 
 " , filtration of, 115-129, 151-153, 157. 
 
 " irrigated land, odors from, 88, 89. 
 
 " irrigation, land for, 86, 87, 93, 98, 99. 
 , effects on health of, 87, 88. 
 
 " , manurial value of, 82-84, 96, 148. 
 
 " , nitrification of organic impurity in, 18-21. 
 
 " pollution of stream, 69-71, 162-165. 
 
 " purification, 149, 150. 
 
 " , purified, 10, n. 
 
 " , putrefaction of organic matter in, 13, 17, 20. 
 
 " utilization, 89, 95, 97, 147, 148. 
 Sewerage, 1-7. 
 
 " , combined system of, 4, 5. 
 " plans, 6, 7. 
 " , separate system of, 4, 5. 
 Slow filtration, 130, 131, 135, 151. 
 Sludge, composition and value, 144-146. 
 Snow and frost, 119, 123, I2-|, 155. 
 Stratification of filtering materials, 117, 118. 
 
 Table of doses of sewage per acre of land, 116. 
 
 " " mechanical analysis of sands, 114. 
 
 " " mechanical composition of filtering material, 112. 
 
 " " size and uniformity of filtering materials, 113. 
 
 " " chemical composition of sewage, 10, 12. 
 
 Temperature on sewage disposal by water, effects of, 37, 38, 43-47. 
 Typhoid fever, 59, 61, 62, 73-75. 
 
1 82 IMDEX. 
 
 U 
 
 United States, sewage disposal in, 90-98, 160. 
 Urine in sewage, amount of, 8, 9. 
 Utilization of sewage, 89, 95, 97, 147, 148. 
 
 V 
 
 Value of sewage, 82, 83, 84, 148. 
 Vital process of sewage purification, 14-26. 
 Voids in filtering materials, 152-154. 
 Volume of sewage, 7, 8. 
 
 W 
 
 Water-carriage system oi sewerage, 4, 27. 
 Water-carried diseases, 59, 60, 65, 73-76. 
 Water supplies and sewage, 163, 164, 166. 
 
 " , filtration of, 63, 73, 75-77, 165-167. 
 
 " , purification of, 66, 68, 72, 73, 78, 149, 151, 165-167 
 Worcester, Mass. , pollution of stream at, 36. 
 
 ZoSglcea, 23-25. 
 
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