XXII

SEWAGE DISPOSAL IN CITIES AND TOWNS*

BY SEVERANCE BURRAGE

INTRODUCTION

A sewerage system is the necessary complement to the public water supply. This is so because the water is essentially the cleanser of the building into and through which it passes. It carries out of the house a vast amount of filth. As the neighborhoods become more crowded, it is obviously undesirable, and even unsafe, to saturate the soil with such polluted water, as would be the case were the old-fashioned cesspools used to receive it. Consequently it becomes necessary, sooner or later, to introduce a general system of sewerage to carry away the filth, not only from the individual houses, but from the city or town itself as well.

Primarily the problem is an engineering one. Pipes are laid in the streets, and these connected with the buildings, so that by gravity or pumping the sewage is removed. Should there be a river or lake, or the sea in the neighborhood, the sewage is oftentimes discharged directly into such body of water, and then allowed to take care of itself. Such a disposal of the sewage, while it may be convenient and inexpensive, is exceedingly unsanitary. It creates a nuisance and menaces the health of neighboring communities. Except in the case of the disposal into the sea, such a dangerous method should, if possible, be avoided. Therefore it is desirous to know whether or not raw sewage can be so treated as to render it inoffensive and safe when it is discharged into a body of water that has several communities bordering upon it.

It has been seen in previous bulletins how serious epidemics have been caused by using sewage-polluted streams and lakes as water supplies. Such streams and lakes, laden with raw sewage, are likely to become public nuisances, even if they are not utilized as a water supply.

It is important, then, from the standpoint of sanitary science, and also of modern civilization, that the municipality should, in some way purify and dispose of its sewage, that it may neither menace the health of its neighbors, nor in any way create a nuisance that would tend to lower the charecter of the surrounding country.

Serious outbreaks of typhoid fever, causing much loss of life, have gradually been awakening the people to the importance of this sewnge-disposal

* Purdue University Monograph -No. 5-issued by the Department of Sanitary Science. Permission to reprint kindly granted by the University which is located at Lafayette, Indiana.

question, and today in the United States and Canada there are a large number of cities that have adopted some system of sewage purification. Several have resorted to the utilization of sewage for irrigation purposes, especially in California where irrigation has become a science by itself. A few towns have been forced to purify their sewage in some way because a neighboring city was obtaining its water supply from that region. Framingham and Marlboro, in Massachusetts, had to do this because the Boston water supply came from that neighborhood. But very few have introduced anything of this kind because it was the proper thing to do. It is something which makes little or no return in money, and this fact has undoubtedly been the chief reason for the non-introduction of sewage purification works. people are apparently waiting until something valuable can be obtained from the sewage; until the income from the sewage plant shall exceed the outlay, which, as far as known today, is a result that cannot in most cases be secured.

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It is well known, however, that sewage can be treated in several ways on a large scale so that an inoffensive and harmless effluent is the result, and, in the following pages, after a short description of what sewage actually is, some of these methods of sewage purification will be described and discussed.

SEWAGE ITS NATURE AND COMPOSITION

Sewage is the matter which passes through sewers: excreted and waste matter, solid and liquid, carried off in sewers and drains."" It is the "drainage water, together with the solid refuse conveyed in it." Ordinarily sewage is made up of a large number of constituents. It contains the waste water from the kitchens, bath rooms and laundries; the urine, faeces, etc., from the water closets, and, in many cities the surface water that is collected in the street drains. As a result of this mixture we have an opalescent, more or less watery liquid, with considerable sediment, a disagreeable odor, and unpleasant and dirty appearance. Its color depends largely on the nature of the industries that are located in the community, certain establishments, such as dye-works, giving a variety of colors at different times.

American sewage is much more watery in appearance than foreign because it is so dilute. We have seen in a previous bulletin how our cities use much more water than foreign cities, and analysis shows that American sewage contains on an average about 99 per cent water and the rest mineral and organic matter. But sewage differs from water very materially in one respect, as it contains no free oxygen. This has all been used up in the oxidation of the organic matter present. It is not a simple chemical oxidation, however, the bacteria being most active agents in carrying on the decomposition. The more oxygen supplied in one way or another to the sewage, the more rapid and complete will be the decomposition of the organic matter. On account of this scarcity of oxygen, the organic nitrogen is only partially oxydized. In other words, we find this nitrogen as tree and a bumenoid ammonia, nitrites in small quantities, but none as nitrates. This process of nitrification, carried on largely by micro-organisms, has a most important bearing upon our modern ideas of sewage disposal, particularly upon the results obtained by discharging the sewage upon the soil, or upon sand filters.

1 Century Dictionary.

2 Standard Dictionary.

An average sample of American sewage contains about one million bacteria per cubic centimetre, and it is because some of these may be the germs of disease that sewage is, from the sanitary standpoint, such a dangerous material. Sewage may contain the bowel discharges of persons suffering with some infectious disease; it may contain the water in which the clothing of diseased persons has been washed, and in numerous other ways it can receive material which contains the living germs of various diseases. Although, owing to the lack of oxygen, these bacteria do not as a rule multiply very rapidly in sewage, nevertheless they are there and the sewage is dangerous. They may even decrease in numbers, and yet their presence, even in very small numbers, is an indication that the danger is still there.

OLD METHODS OF SEWAGE DISPOSAL

The most common method of getting rid of city or town sewage has been and is to simply discharge the contents of the sewers directly into some body of water, as a river, or a lake, and then allow it to take care of itself. If discharged into the sea, the salt water has a decided precipitative action upon the sewage, rendering it much less offensive. But when this is done, it is of the utmost importance that all such refuse be discharged at such a time of tide that none shall be carried back to the beaches, where it would become a nuisance. But there are numerous cases in the United States where the raw, unpurified sewage of good sized cities is discharged into bodies of fresh water. The self-purifying power, a more or less uncertain factor, is depended upon to convert this dangerous, filth-polluted water into a safe and inoffensive liquid. Under favorable conditions, such as enormous dilution and swift currents, it is undoubtedly purified to a large degree, but even then the water could hardly be considered an absolutely safe drinking water.

This system of simply discharging the sewage into fresh water we will not regard as a method of purification. It is one which has caused a great deal of legislation in foreign countries as well as at home. It gave rise in England to the Rivers Pollution Commission. It is going to be given an extraordinarily good trial at Chicago, where the sewage is to be washed down the drainage canal by means of the lake water into the Illinois River. The authorities claim that the dilution will be so great that no disagreeable or dangerous effects will result to those living down the river.

MODERN METHODS OF SEWAGE PURIFICATION

The old theory that filth, containing pathogenic or disease-producing organisms, would, when exposed to the sun, propagate contagious diseases, has been entirely overthrown. Experimentally and practically, sewage has been discharged upon the land, which may or may not have been especially prepared to receive it, with the result that the pathogenic organisms and the offensive nature of the material are most effectively destroyed.

If the sewage be discharged on to a piece of land for the purpose of enriching the soil for raising crops, it is known as irrigation; if over a large area, broad irrigation. When it is poured upon the land, usually especially prepared, with no idea of raising crops, it is known as filtration; and as the best results are obtained by not pouring the sewage on such beds continuously, it is then spoken of as intermittent filtration. It is quite common to have a combination of the two methods, broad irrigation and intermittent filtration, which has given very good results.

The following description of a broad irrigation plant is given by Palmburg.'

BROAD IRRIGATION

The fields should be divided into sections 30 to 50 feet square, raised in the middle and having an equal slope. The sewage is conveyed by a culvert to the middle of the section. At certain distances in this culvert dykes are placed, causing the water to overflow on the slopes of the section.

The suspended matters in sewage tend to become deposited on the surface, forming a layer almost like a bed of felt. It may entirely cover the soil and choke the vegetation. In England its formation is prevented by means of reservoirs, in which the sewage stands, to allow of suspended matters being deposited. Solid matters may also be separated by a grating or precipitated by means of preliminary chemical treatment.

Winter, especially in cold countries, causes some difficulties in the application of irriga. tion. The absorptive power of the earth is feeble with a low temperature; there is no active growth of vegetation. Under these circumstances the system becomes one of simple filtration. * ** From a sanitary standpoint, the system of irrigation has had a most satisfactory effect. Numerous critical observations, especially in England, have failed to show the origin of any case of contagious disease from it.

Since 1870, when the Rivers Pollution Commission proposed in their report the purification of sewage by irrigation of cultivated land, the system has been introduced into over 145 English towns. Other European towns, including Berlin, Breslau, and Dantzig have also adopted it.

In America there are several good examples, among which are Wayne, Pa.; Pullman, Ill.; Berlin, Ont.; and Greenfield, Mass. Farther west, where water is scarce, sewage has been utilized for irrigation with considerable success. In California: Fresno, Pasadena, Redding, Los Angeles, Santa Rosa, and Stockton, all irrigate with sewage. In Colorado: Colorado Springs and Trinadad do the same; as do Helena, Mont., and Cheyenne, Wyo.

INTERMITTENT FILTRATION

The word filtration, as used now in connection with water and sewage purification, has come to mean much more than the simple mechanical removal of particles of mud, filth, etc., from the material being filtered. Certain chemical changes take place which can be accounted for only by the presence in the filter of living micro-organisms. Remove these soil bacteria by sterilization, and the filter loses for a time its power of purification. Furthermore, the filter is much more effective when air is present, and thus came the process of intermittent filtration, in which the sewage is poured upon the especially prepared filter bed for a definite time and then the filter is allowed to rest. The sewage, as it sinks into the soil, drags or sucks air after it, which apparently adds greatly to the vitality of the organisms in the filth. This, then, is the theory of intermittent filtration, that beside the actual sifting process of the sand, the filter itself has a vital action that is dependent more or less upon the air which the intermittent discharge of the sewage gives access to the interior of the filter. Thus the presence of the air increases the nitrifying or oxydizing power of the filter, both by virtue of the oxygen present in the air and by the additional activity which its presence lends to the micro-organisms.

Experimentally, much work has been done at the Lawrence (Mass.) experiment station upon intermittent filtration, where sewage was passed I A Treatise on Public Health and Its Applications. Albert Palmburg, p. 140. 2 Public Health and Its Application. Palmburg, p. 138.

through various thicknesses of various soils. It was found, among other results, that some forms of bacteria would pass through certain filters more readily than others; that in certain cases where the numbers of sewage bacteria had increased while the sewage was passing through the filter, the kinds of bacteria had greatly diminished, and so on.

Practically intermittent filtration has for some time been in operation at Gardner, Mass., Marlborough, Mass., Summit, N. J., Medfield, Mass., South Framingham, Mass., Brockton, Mass., and Hastings, Neb. The latter city being situated, as a good many western cities are, with no available outlet for their raw sewage, will be a good one to describe here in some detail as an example of considerable value. The facts are taken from Baker's Sewage Purification in America, in which the description was prepared by the engineer, Mr. J. M. Wilson of Omaha, Neb. As Mr. Baker1 says: "One feature of the design and management of the Hastings plant is worthy of special notice and commendation. Purification is recognized as the first object to be obtained in disposing of the sewage, the raising of crops for revenue being made the second."

The land upon which the sewage is disposed is one and one-half miles from the city. It was graded into ten areas about two acres in extent, each area having its own level and separated from the adjacent areas by a low ridge of earth. These areas were brought to a uniform grade, except at the points where the sewage is received from the distributing gutters. Here the surface was slightly elevated to secure a better distribution of the sewage. The sewage is brought from the city by gravity to a settling and distributing tank, which is provided with cast iron gates for controlling the flow. Each area receives the sewage for a day or two at a time, followed by a rest until the sewage has been applied in succession to the other areas. The application of the sewage to the land creates no nuisance and causes but very little odor.

Brockton, Mass., has one of the most recently completed systems of sewage disposal and seems to promise the very best of results. Here again is the combination of filtration and irrigation. Vassar College, at Poughkeepsie, N. Y., has recently adopted the purification by irrigation and filtration with remarkable success.

To give the reader an idea of how complete the purification of the sewage is by this combined irrigation and filtration method, the writer describes the following occurrance during a visit to the South Framingham, Mass., plant in July, 1896, and while being shown around by the man in charge, all of the party, three in number, drank the water from the effluent underdrains. The water in no way indicated its origin by temperature or smell, although, it did taste quite soft. It might easily be mistaken for spring water as it came out of the pipe into the ditch, clear aud sparkling. The principal crop on these sewage beds was corn, which was growing most luxuriantly.

SEDIMENTATION

In Amherst, Mass., the sewage is collected in a stone tank 15x20x6 feet, divided into two equal compartments, in which the sewage is allowed to settle. This division into two compartments enables one to be cleaned of its sludge while the other may be receiving the sewage. The sludge is

1 Sewage Purification in America. M. N. Baker, p. 49.