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Vol. 19, No. 4
An Outline of Sewage Purification Studies at the Lawrence Experiment Station’ By H. W. Clark2 MASSACHUSETTS DEPARTMENT OF PUBLIC HEALTH, BOSTON,
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N T H E early eighties of the nineteenth century there was a great increase of interest in sanitary science. There were three main reasons for this: first, the growth of population, especially the urban population in England, Germany, and America, which made the questions of water supply and sewage disposal of the growing municipalities of those countries especially pressing; second, the general acceptance of the theory of water-borne disease; and, third, the establishment of the science of bacteriology on a fairly sound and practical basis by the work of Louis Pasteur and Robert Koch. It was during this period that the State Board of Health of Massachusetts, under the leadership of Dr. Henry P. Walcott and Hiram F. Mills, C. E., started, among other sanitary innovations, the Lawrence Experiment Station. Some work was accomplished there in 1887 and by 1890 this work had progressed far enough to arouse interest throughout the entire sanitary world. The station was established primarily to learn how to purify sewage and water. The investigations upon these two subjects during its early years of operation were the first elaborate systematic work under scientific auspices along these sanitary lines. Previous work on a very small laboratory scale had been done by Frankland and Warrington in England and Schloesing and Muntz in France, and of course municipal water filters and sewage farms were even then (1887) of long standing in England, France, Germany, and elsewhere in Europe. This Lawrence work upon the treatment and purification of water and sewage, in connection with other activities carried on a t the experiment station, has been continued for thirty-eight years; and, since the first three or four years during which much attention was given t o it by Mr. Mills, has been all planned and directed by chemists and bacteriologists, and has been very largely upon such problems of sanitary engineering and sanitary science as can only be successfully studied by a combination of chemistry, bacteriology, physics, and hydraulics. The reports of the station have been more familiar the world over to engineers than to chemists, and the station has been, among other things, a school of sanitary and hydraulic engineering. Many of the chemists and bacteriologists who have worked in its laboratories and among its filters and other apparatus for treating sewage, water, etc., have since become well-known sanitary and hydraulic engineers, and in several instances distinguished in their profession the world over. The act of the legislature giving the State Board of Health oversight of the water supplies of the state and authority to conduct investigations in regard t o the purification of sewage, water, etc., was passed in 1886 and the report of the board for the year 1887 contained an account of the establishment of the station and its preliminary work. A chemical laboratory was installed in 1888 and a laboratory for bacteriological and microscopical work in 1890. These laboratories, always modest in size and equipment, Received November lS, 1926 Chief chemist of t h e Massachusetts Department of Public Health The writer has been a n d director of the Lawrence Experiment Station connected with the Lawrence work from its inception a n d director since August, 1895. 1
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MASS.
have been enlarged from time to time and in them many new and more accurate chemical, biological, and physical methods for the study of water, sewage, sand, soils, etc., have been developed. Besides these laboratories, the station has always had its hydraulic or experimental laboratory equipped with tanks, filters, and other apparatus for experimental work. Beginning with studies of intermittent sand filtration of sewage and water, together with laboratory investigations of nitrification, the cause of the reduction of bacteria by filtration, etc., the work of the station grew constantly. It has included many long-continued investigations, all tending toward the development of modern, economical, and practical methods of sewage purification, the purification and disposal of manufacturing wastes of many kinds, the filtration or other treatment of water, and other special problems in sanitary science. I n pursuance of this work, continued now for more than thirty-eight years, over five hundred filters and scores of tanks of different construction and operation and other experimental devices have been operated to investigate the many scientific and practical problems arising in water, sewage, and industrial waste treatment and purification. The analyses made-chemical, biological, and physical reach well into the hundreds of thousands and the printed pages describing and summarizing all this work mount well into the thousands, distributed through thirty-seven annual reports and more than one hundred monographs on research work of especial interest. This work has placed on a sound basis the broad, general principles of the purification of both sewage and water and has also beenexceedingly useful and important in solving special problems arising constantly in regard to the sanitation of a thickly populated industrial state. To summarize this work in a short article would of course be impossible, hence the following pages are intended to indicate only a few of its main features. When the investigations were begun intermittent filtration through sand was the only known biological method of sewage treatment other than broad irrigation or sewage farming. As the work a t Lawrence continued, methods of treatment were developed there by which the volume of sewage that could be treated and purified upon an acre of land daily was increased from an average of 50,000 to 75,000 gallons by intermittent sand filtration to approximately 15,000,000 gallons by aeration with living sludge-the SOcalled activated sludge process. I n other words, a tremendous advance in the economics of treatment took place from methods allowing a maximum disposal of the sewage from 500 to 750 people per acre per day by filtration to methods that would purify the sewage of 150,000 people in aeration or activated sludge tanks built on a similar area. The history of this accomplishment can readily be traced in the yearly reports of the station and is summarized to some extent in this article. I n the first elaborate report of the work of the station, a special report in 1890 entitled “Filtration of Sewage and Water and Chemical Precipitation of Sewage,” the following statement was made:
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Experiments of Schloesing, of bIuntz in France, :and of Warrington in England tended to prove that nitrification in a liquid never takes place but with the aid of organisms introducing into the process the conditions of organic life. -4s nitrification takes the leading place in the process of purification in sewage, we must then regard as essential to the process the conditions most favorable t o the action of the organisms whlch produce nitrification. Among these conditions experiments had already shown that the presence of oxygen was essential; so was the presence of organic matter, of moisture and of some alkali, and the temperature should be nearly that which IS favorable for plant life. Such organisms had been known t o exist either in sewage or in the material of which some filters were composed and when existing with the other conditions favorable for producing nitrification, large quantities of organic matter could be converted into inorganic and mineral matter.
Intermittent Sand Filtration Although, as this statement makes clear, something was known when this work was begun about the bacterial and chemical results produced when sewage was applied to beds or filters of sand, little or no data had been accumulated upon which to formulate the laws governing intermittent filtration or its economic and engineerins features. Therefore, since to put the science of intermiltent sand filtration upon a practical basis was the first work undertaken, sand filters of different depths containing different grades of sand were constructed and operated. The chemical and bacterial results showing the degree of purification of each were studied and the physical and hydraulic features of each grade of sand used and each filter in operation determined. It was stated as a result of this early work that purification of sewage by intermittent filtration depended upon oxygen and time, all other conditions being secondary; that any treatment which kept all particles of sewage distributed over the surface of the sand particles in contact with an excess of air for a sufficient time was sure to give a welloxidized effluent and the power of any material to purify sewage depended almost entirely on its ability to hold the sewage in contact . with air; that imperfect purification could invariably be traced either to a lack of oxygen in the pores of the filter or to too rapid passage of the sewage through the filter. The amount of open space in each grade of sand used in filtration filled with air and sewage during purification was carefully determined, also the relation between the grade of sand of a filter and the volume of sewage that could be applied to a given area a t one time. Filters of coarse sand with slight retentive capacity were shown to necessitate frequent applications of small volumes, while finer sands with smaller spaces between particles, hence more resistant to flow, could take much larger volumes but a t less frequent intervals. On the whole it worked out, however, that within certain limits each grade of sand that could be successfully employed would purify about the ssme amount of sewage in a year, and that the retentive capacity of filters of coarse sand was increased the longer 1,hey continued in use, owing to the accumulation of stable organic and inorganic matter within them, with the consequent lessening of the total open space of the filters and decrease in the sizes of the passages between and around the sand grains. It is worthy of note that none of the sand filters first constructed were put out of operation because of clogging, and that three of these filters started nearly forty years ago are still in operation and undoubtedly can be continued in operation purifying sewage indefinitely. Experiments with oxygen, in which the amount required for nitrification was determined by the operation of a filter in which the actual volume of oxygen present was controlled, established the fundamental law of sewage purification that, not only is nitrification an oxidizing process which can
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take place only in the presence of free oxygen, but only so much oxygen need be present as is necessary for the maintenance of aerobic conditions provided this oxygen is evenly distributed throughout the filter. That is to say, a filter can be operated successfully with a minimum amount of free oxygen-that is, with only 1 or 2 per cent of oxygen in the atmosphere within the filter. Many experiments were made to determine the effect upon nitrification of an excess of a number of substances which may occur naturally in sewage or may a t times be introduced into it. Albumin, peptone, ammonia, alkalies, acids, salts, sugar, soap, phenol, mercuric chloride, formalin, arsenic naphthalene, sulfides, hypochlorite of lime, chlorine gas, etc., were all investigated. These experiments all illustrate the adaptability of the nitrifying body to the conditions imposed upon it during each experiment and established another fundamental law of sewage purification-that if nitrification is to continue in the presence of an excess of any substance, the filter must become slowly accustomed to that substance by application of it in gradually increasing amounts. When once accustomed to considerable amounts of any substance the process of nitrification will generally proceed unimpaired. It was found in the course of these studies that the volume of sewage that can be purified by intermittent sand filtration is, within reasonable limits of strength of sewage, determined rather by the amount of organic matter present than by the volume of sewage in which this organic matter is held. This was illustrated by operating filters with unit amaunts of organic matter in varying volumes of diluting water. That the rate of operation of a filter can be increased theoretically only in proportion to the degree of removal of suspended matter in the sewage was shown by removing this suspended matter by settling tanks, chemical precipitation, septic tanks, two-story tanks, straining through coarse media, and by operating sand and other filters a t rates proportional to the matter in suspension, that is, in the sewage applied to them. During these studies of sand filtration of sewage and water, investigations were continually made of the chemical and physical properties of the sands and gravels used in filter construction, and certain of these studies were summarized in 1892 in an article entitled “Physical Properties of Sand and Gravel with Special Reference to Their Use in Filtration.” This article described the methods evolved for such examinations and for determining the limitations of each material in regard to the flow of water and the efficiency that might be expected of each in sewage and water filtration. The methods given and the terms “effective size” and “uniformity coefficient,” there first used and defined, have since been used by practically all engineers wherever sewage or water filters are to be constructed; that is, this article standardized sand analysis. Gravel-Stone Filters I n 1889, a filter of small gravel stones was constructed and put into operation, and it was found that rates of operation much higher than could be obtained with sand filters were possible owing to the much larger open channels through this gravel-stone material. It was found feasible to operate this filter at a rate of 250,000 gallons per acre daily with good nitrification and fair removal of organic matter. As this filter was continued in operation and it was found that sewage could be actually purified by it at a rate a t least four times as great as through a sand filter, the law was evolved that, The mechanical separation of any part of a sewage by straining through sand is but an incident which under some conditions favorably modifies the results, but the essential conditions of
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filtration are very slow motion of thin films of liquid over the surface of the particles that have spaces between them sufficient to allow air t o be in contact with the films of liquid. With these conditions it is essential that certain bacteria be present to aid in the process of nitrification.
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t o such an extent that filters could be operated often for ten, fifteen, and twenty-five years with but little cleaning of material except of the few surface inches. It was stated early in this work that sprinkling filters were simply devices for the modification of sewage, or, in other words, the quick oxidation of the putrefying matters present, while allowing the larger body of stable matters and matters rendered stable by filtration to pass through, and not a substitute for sand filters which remove practically all the matters in suspension in sewage. Sprinkler nozzles and dash plates were tested to determine uniformity of distribution over these filters. The effect of different materials, used for the construction of such filters, upon increasing uniformity of distribution was also tested. Contact Filters
I n 1892 gravel-stone filters with forced aeration were started, and these were followed by filters constructed either of broken stone, coarse clinker, or coarse coke. It was found that purification with good nitrification could be obtained a t rates ten and twenty times as great as by intermittent sand filters. I n all these filters good nitrification occurred and the amount of aeration was cut down from time to time until it approximated only about two hours out of each twenty-four. These filters produced effluents of the true trickling filter type-high in nitrates, containing much free ammonia and stabilized organic matter in suspension. The fact that filters of this type oxidized the putrefying, unstable matters of the sewage and allowed the residual From 1894 to the present day purification by contact stable matters to pass with the filter effluent was discussed filters has been studied, including such subjects as efficiency in the 1895 report. To all these first high-rate filters of of contact filters of different materials, double-contact coarse media the sewage was applied, not from sprinkling filtration, permanency of contact filters, disposal of nitrogen nozzles, as this was a later development by Corbett a t Sal- by contact filters, composition of organic matter stored ford, England, but from automatic devices, siphon action, within them, best methods of operation, together with tipping basins, etc., which gave frequent applications of the rates that could be followed with such filters of different sewage (on some of the filters sixty or seventy applications material and different depths. daily). Finally, as this work continued the filters were operated without artificial aeration, as it was found that Studies of Manufacturing Wastes the sewage could be applied in such a manner that a plentiful Beginning in 1895 much attention was given to studies supply of air would always remain within the filter to mainof the purification of wastes from manufacturing industries, tain the proper biological activity for oxidation and nitrification. Gradually the filters were increased in depth and as a result reasonable and efficient methods for the until in 1899 filters 10.5 feet deep were constructed and treatment of many of these wastes have been developed. operated, and one such filter started in that year is still Among the wastes studied are those from tanneries, paper mills, carpet mills, paint mills, woolen mills, wool-scouring in existence. The operation of these filters greatly changed the opinions works, dye works, silk mills, shoddy mills, creameries, as t o the length of time necessary for sewage to be held yeast factories, glue works, gas works, etc. A special article within a filter to be purified. Early investigations showed in regard t o such as had been studied up to 1909 was pubthat, through filters 10 feet in depth and constructed of lished in the report of that year and the many studies since broken stone, applied sewage would appear a t the outlet made upon the purification of such wastes hare been sumwithin an hour of application, and that within three hours marized generally in the annual reports. These studies of mill waste purification proved that a t a large part was escaping from the underdrains although the rate of the filter was but 1,500,000 gallons per acre daily. times good purification and a satisfactory effluent could be With greater rates the time taken for passage of the sewage obtained without any apparent nitrification. As many was shown to be much less. With filters constructed of of these wastes contained large amounts of carbonaceous rough material, such as clinker, the sewage was held within and small amounts of nitrogenous matters, studies were the filter for a longer period but still passed through rapidly made that seemed to show that nitrification in filters decompared with the passage through sand filters in successful pended upon the relation of the amount of carbonaceous operation. It was found as the work with these filters to nitrogenous matter present in the liquid undergoing continued that, for reasons not a t first understood, trickling filtration; that is to say, nitrification could apparently filters 10 feet deep were more than twice as efficient as filters proceed when the nitrogen was represented by x and the 5 feet in depth and could be operated a t much higher rates carbon by lox, but would be eliminated when the carbon than the greater depth would appear to warrant. Finally, was increased to 122 or 152. Special experiments were in 1913 trickling filters were put into operation to determine made to study this point. a t what rates such filters constructed of different depths Chemical Precipitation and of the same material must be operated in order to obtain Chemical precipitation, one of the earliest forms of modern effluents of equal quality. These filters were 4,6, 8, and 10 feet deep, respectively, and it was found that the 10-foot sewage treatment and still widely practiced, especially filter could operate at a rate, not two and one-half times as an efficient preparatory process for the newer methods as great as a 4-foOt filter, but from eight to ten times as great of filtration, was investigated almost a t the beginning of and give equal purification results, and that an 8-foot filter the Lawrence works. I n 1889 an extensive investigation could be operated a t nearly or quite twice the rate of a 6-foot was made in which data were obtained as to the relative filter with equal purification results. This phenomenon efficiency of different chemicals and to show how this process was shown to be due entirely to the hydraulics of the flow should be controlled to obtain the best results with the greatest economy of operation. These studies were sumof sewage through this coarse material. Studies in regard to the storage of organic matter in marized in the special report on the purification of sewage trickling filters, etc., showed clearly that, owing to the action and water, 1890. Following this for five years, further of bacteria and minute animal life, there were periods each studies were made along. this line and the resulting clarified year when the held organic matter became loosened and liquor was applied to the filter in operation a t the station, passed away from the filter in the effluent, this occurring this chemical precipitation work being carried on in com-
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parison with the results obtained under similar conditions and time by ordinary settling tanks, strainers, etc,.
The article discussed the results from certain sewage farms of large area in different parts of the world and stated that:
Septic T a n k s
Only under the most favorable conditions can the return from these farms be made to pay operating expenses, and an instance is yet to be cited where these returns pay both the cost of operation and interest on the capital invested. The exceptions perhaps to this are certain tracts or farms in regions of low rainfall where the sewage is valuable as a liquid, that is, for real irrigation purposes. Much of the valuable fertilizing and fatty constituents of sewage is found in the matters in suspension. Average American sewage contains perhaps about 2100 pounds of sedimentable matter in a million gallons, and the nitrogen, fatty matters, etc., in this 2400 pounds of sludge are worth approximately $15 or 818. In order, however, to reclaim this valuable material, sludge must be dried, pressed, and also subjected t o a process for the separation of grease from the fertilizing constituents in the remaining body of the sludge. Only by this separation can the grease become an article of commerce and the sludge of real agricultural value.
For many years beginning in 1898 septic tanks of different shapes receiving sewage of different character and allowed different periods of storage were in operation, and in recent years such t’anks have again been operated especially to show their use and efficiency in the treatment of household, hotel, or factory sewage, and their effectiveness as sludge destroyers. While this method of sewage treatment has lost favor in recent years as the tendency has been towards the construction and operation of two-story tanks-that is, tanks with separate sludge compartments-yet many important data were accumulated by this work a t Lawrence. The actual percentage of destruction of organic matter in different tanks and with sewage of varying composition was determined and the volume and composition of the gases set free from these tanks were accurately measured. In the report for 1899 it was stated: The observation that the stronger the sewage entering a septic tank the greater the percentage removal of organic matter suggests the idea that where exceedingly large volumes of sewage are t o be purified, the sewage can be passed through ordinary settling tanks so constructed that the sludge settling t o the bottom of the tanks could be flushed into a septic tank and this sludge alone be treated by septic action.
Al tank based upon this principle was put into operation on So\-ember 15 of that, year. This was the first separate digestion compartment two-story tank similar to what is generally known as Imhoff tanks. This was acknowledged by Dr. Tmhoff in his paper before the Congress of Hygiene in 1912 and in a letter to the writer. The Travis tank, first put into operation a t Hampton, England, was also based on the Lawrence work, as stated by Travis more t’han twenty years ‘ago. During 1912 and 1913 studies of sludge digestion were made in tanks 17 to 30 feet in depth and with sludges of different composition and treated in different ways. The results of these experiments showed that the production of an inoffensive sludge in these deep tanks was dependent largely on the character of the sludge, but in certain cases slight changes in the operation of the tank or the addition of certain chemicals to the sludge were sufficient to make the process effective in producing an odorless, well-digested sludge. The results also showed that where a well-digested and odorless sludge was produced fermentation was more or less active; that when fermentation did not begin in a tank containing any of these various sludges, it could generally be started by making the sludge slightly alkaline by adding lime or other chemica.ls. During the past year hydrogen-ion control of such tanks has been studied. Fertilizing Value of Sewage Sludge
I n connection with all this work upon sludge removal by settling, chemical precipitation, and septic tanks, many studies were made in regard to the value of t,he fertilizing materials in sewage and sewage sludge, and in 1912 a special article was issued entitled “The Fertilizing Value of Sewage and Sewage Sludge-A Sanitary and Economic Problem.” This article in conclusion stated that: The total amount of fertilizing matters in each thousand gallons of representative American sewage is not worth above six or eight cents. Of this, about half is represented by the ammonia in solution and there is no method by which this material can be utilized except by application of the sewage to land.
Further statements were made that: This drying, pressing and separation of grease caused greater outlay than the total value of the fertilizing materials recovered,
The conclusion of the article lyas that: Sludge has value and as the processes of drying, pressing and fat separation are improved, and also as nitrogen advances in price, as seems inevitable, sewage sludge will become or greater agricultural value than i t is a t present, especially as the basis of a fertilizer enriched by the addition of potash, phosphates, etc. Destructive Distillation of Sludge
Many studies were also made in regard to the destructive distillation of sludge from different tanks, etc., to show t’he amount of gas produced per ton of dry sludge, the coniposition of these gases, and their possible use as sources of light and heat. Activated Sludge Process
A special article in the report of 1912 described a study of fish life and river pollution, the disposal of sewage by dilution, and the effect of pollution upon fish life, together with some observations as to the efficiency of aeration and growths in sewage purification. h chapter entitled “The of deration of Sewage as An Aid to Filtration-Collection Suspended and Colloidal Matters” was included in this report. I n these first experiments sewage was aerated 7-igorously in bottles and carboys and it was found that by this aeration and agitation of the sludge, good purification of the treated sewage was obtained-that is, after a period of aeration and settlement of sludge, a clear, supernatant liquid could be withdrawn, high in nitrates and stable. It was found that in order to obtain these results day after day, the sludge, after the withdrawal of the supernatant liquor, must be continually agitated with air. It was also noticed that when this work was carried on in the light in glass vessels green algal growths appeared, but these green growths were by the act of aeration thoroughly mixed with the characteristic gray and brown sludge growths. When, moreover, the work was carried on in tanks from which light was excluded, only brown and gray growt’hs occurred in the sewage and yet, practically the same degree of purification was obtained. It was found as this work went on that apparently the greatest degree of purification was obtained when, in addition to aeration and circulation of sludge, certain matlike or spongelike growths, gray and brown, grew upon the sides, etc., of the carboys and tanks used. Therefore, to test out the added efficiency of the process by such growths, tanks containing a certain number of slates upon which such growths could occur were put into operation. On a small scale this seemed a feasible method,
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but engineering reasons, especially cost, prevented the use of such baffles or colloiders in large construction. I n these tanks, as in the carboys and bottles, good purification was obtained and the sludge remaining after the purified supernatant sewage had been withdrawn from them was constantly aerated until sewage was again introduced. The advantages of this live sludge or activated sludge process are the very large volume of sewage that can be purified on a limited area, the fact that the nitrogenous content of the sludge is increased by the coagulation and collection of colloidal matters in the sewage, and that the fatty matters are so greatly decreased that the sludge when dried and otherwise suitably prepared is available as a fertilizer. The name “activated sludge process’’ was given by English workers, one of whom visited the Lawrence Experiment Station in November, 1912, and afterwards repeated the Lawrence work.
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principal sewage filters of different types, showing the great efficiency of fine sand filters in removing bacteria and the reasons for the varying results from filters and tanks being operated in various ways. It has been an interesting and fruitful subject, but of course the object of sewage purification is not to make drinking water out of sewage but simply t o convert it into an inoffensive liquid which may be disposed of by dilution in a convenient stream without causing a nuisance. To make the water in a stream pure enough for drinking is a separate problem. Relation of Work at Lawrence to World Sewage Purification
This paper gives only the barest outline of this Massachusetts work. From the beginning the station has been visited by a constant stream of engineers, chemists, biologists, students, and others interested in the purification and treatment of sewage and water. These visitors have come not only from this country and Canada but from countries Bacteriology Studies in Central and South America, from England and practically When the Lawrence Experiment Station was started, every country in Europe, from Japan, China, India, Ausbacteriology and bacteriological methods were in their tralia, and, in fact, from all places where problems of water infancy. Only six years before that date Koch had pro- and sewage arise. posed the use of solid media by means of which quantitative It is, of course, true that during the past twenty years, determinations of the numbers of bacteria and the isolation exceedingly important and large-scale investigations of and study of species of bacteria became possible. The sewage disposal have been made by many municipalities use of the Petri dish, which extended the scope of the Koch in this country, England, and Germany. These investimethods and made possible the rapid and accurate bacterial gations have attracted much attention and have been of examinations, now so common, was proposed in the same far-reaching importance. In this country extensive experiyear that the Lawrence experiments were inaugurated, but mental work has been carried on at Worcester, Baltimore, Columbus, Chicago, Milwaukee, and many other places. was not generally adopted until several years later. The bacteriology of sewage and its purification was an Moreover, in this country and abroad many large, costly, unexplored field. Almost from the beginning, determinations and modern sewage disposal and purification plants have of the numbers of bacteria in sewage and in the effluents been built. In England such plants are numerous and from the various filters and in the filtering material were operated under good technical control. With us, modern made a part of the investigations, and the results of these disposal is illustrated by large plants a t Fitchburg, Worcester, bacterial analyses and of the special investigation which Baltimore, Columbus, Chicago, Milwaukee, Indianapolis, they suggested did much to explain the cause and effect and many other municipalities. These large plants furnish of sewage purification by intermittent filtration and to certain data in regard t o modern methods, such as cost of forecast the results which would be obtained by other meth- operation, etc., that are more reliable than data obtained ods of treatment. Among the subjects first studied were from small experimental plants. Nevertheless the Lawrence the relation of numbers of bacteria in the effluent from a Experiment Station still furnishes information in regard to filter to its rate of flow, the effect of grade of sand, the water and sewage treatment and other special problems effect of intermittent filtration upon bacteria, the effect of sanitary science, and its staff constantly strives to add to of the completeness of nitrification, studies of the bacteria the knowledge of the world in these matters as well as t o of nitrification, etc. Through all the years since then, aid in solving the state and municipal problems of Massathe bacteriology of sewage treatment and purification and chusetts. Finally, the relation of this Lawrence work to the larger the value of bacterial work of different kinds in solving sanitary problems and in estimating the degree of purification field of sewage purification in all parts of the world has often of water, sewage, etc., has been investigated, together with been stated clearly, not only by American but by English, much other bacteriological work dealing with subjects other German, and other engineers and scier,tists in books upon than water and sewage. Chapters have been given in sewage disposal, articles in engineering journals, and in many different reports in regard to the hygienic efficiency of the appreciative letters to the author of this paper.
Methods for Meeting Smoke Problem in Cities Methods utilized by several large cities in meeting the smoke problem are set forth by Dr. Charles White, pathologist of the United States Health Service, in the American City for February and in the monthly bulletin of the Newark Department of Health for last October. In the first article Dr. White points out that smoke prevention will be more readily secured if it can be shown that smoke-laden atmosphere has a harmful effect on the human system. The chief arguments heretofore have been for comfort and cleanliness. Data collected by him show that the City of Pittsburgh has a low tuberculosis death rate but a high pneumonia death rate, a n analysis by wards showing that the higher rates occur where the smoke-laden air is denser. The number of physicians specializing in respiratory diseases is higher per capita in Pittsburgh than in Baltimore, showing a greater demand for this
type in the smoke areas. The evidence indicates that smoke must be controlled from the viewpoint of its effects upon public health. The second article deals with Newark’s new smoke ordinance, which was made necessary by the increased use of soft coal during the hard coal strike in the winter of 1925-26 and its continued use in spite of the present availability of hard coal. This new ordinance creates a Bureau of Smoke Abatement. Dense smoke may be produced for a period of not more than six minutes in any one hour; it is unlawful for any locomotive to emit dense smoke and firing is prohibited when the locomotive is not in motion. The standard in use is the Ringelman Smoke Chart, and any smoke comparable with grade 3 or higher is considered to be dense. The effects of this ordinance are already apparent in the clarification of the atmosphere in the City of Newark.
