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ation is being used to finance the European war. The telephone company persists in supplying poor service at extortionate rates. The gas company for reasons best known to itself continues to use the expensive and old fashioned process of water gas manufacture, necessitating the use of enormous quantities of gas oil, when other progressive cities are enjoying the benefits of the modern coke oven gas process. These and many other problems are immediately before us; and it is our hope that the members of the next Legislature convening in Springfield will see to it that the proper action is taken to grant Chicago and other municipalities power sufficient in extent and scope to enable us to prosecute our work in a manner that will result in great and lasting benefit to the people.

BY PAUL HANSEN, ENGINEER, STATE WATER SURVEY

Sewage disposal is one of the most complex and at the same time one of the most unwelcome problems with which a municipality must deal. It is complex because there is first a great variety of means and methods from which a choice may be made and, secondly, the influence of local conditions is so great that a rational solution of the problem cannot be reached unless all local conditions are given careful and detailed study. It is unwelcome because the resultant benefits from costly disposal works generally accrue to riparian owners in a downstream direction rather than to the community itself. For this reason inoffensive sewage disposal is rarely taken up until forced upon a community by threatened damage suits or by order of the state board of health or other central authority; and when it is taken up the usual experience is that all funds available have been used for other purposes. About the only hope for speedy relief to and just treatment of aggrieved parties so far as municipal sewage disposal is concerned is the authorization of some state authority by legislative act to permit under proper restrictions and safeguards the issuance of bonds, payable out of the general taxation and in excess of the present limit imposed by law. The cities of Decatur, Bloomington and Galesburg are now facing this situation; and it will be a matter of relatively few years before Springfield, Elgin, Aurora, Danville and many other cities must face it also.

Within the limits of a short paper, no sufficiently comprehensive discussion of sewage disposal methods can be given to enable one to decide what method or methods are best applicable to any given set of local conditions. A brief description of a few of the most important devices

and a few remarks as to the conditions under which they can most advantageously be used may, however, be of in terest.

Disposal of sewage by dilution is by far the most com. monly used and where applicable is a method recognized as an entirely proper one. To certain extremists and idealists, disposal by dilution is regarded rather as an absence of method and a mere crude expedient that should not be tolerated. Those, however, who have given the subject most study and thought believe that streams may be used as drainage courses for sewage and industrial wastes without offense and without injury to public and riparian rights, provided the method is carried out scientifically. Properly to dilute crude sewage, there must be broadly speaking, from four to six cubic feet per second of normal unpolluted flow in the stream receiving the sewage to every 1,000 persons contributing sewage at any one point. The sewer outlets must be so constructed as to secure a rapid and thorough mixture of the sewage with the water of the stream. Frequently it is desirable to screen the sewage before discharging into a stream and this is accomplished by screens varying from very fine to very course, depending on circumstances. Screens are primarily serviceable in removing unsightly floating matters, but the very fine screens are also effective in preventing the formation of sludge banks.

In sluggish streams even where dilution is adequate, it is generally necessary to remove the settleable solids in sedimentation tanks, otherwise sludge banks will form which, when in a state of active decomposition, create foul odors and unsightly conditions.

When disposal by dilution is not permissible because of the absence of a sufficiently large stream or other body of water, it becomes necessary to resort to some form of land treatment. Application of sewage to farm land, or sewage farming as the process is generally called, was the first method of land treatment resorted to. This method which is highly developed in some European countries appeals

to the imagination because of the possibilities which it affords of utilizing the moisture and conserving the manureal value of the sewage. While sewage farming has had a degree of success at Berlin and Paris, where conditions of labor, climate and soil have been especially favoraable, the process broadly speaking has not displayed economic advantages over the more intensive processes that make no attempt at sewage utilization. Particularly in America, sewage farming has not been found economically applicable; and even in the arid west, it has found but very limited adoption. As a method, however, it should be kept in mind because there occur from time to time peculiar conditions under which it may be adopted economically and effectively.

Broad irrigation differs from sewage farming only in that the former places emphasis on disposing of the sewage while the latter places emphasis on growing crops. Areas required for these processes vary from two to ten acres per 1,000 persons contributing sewage.

Intermittent sand filtration represents the first step toward intensive methods and consists in the application of sewage once or twice per day on well underdrained sand beds either natural or especially prepared. With this method an acre of beds can purify the sewage from 300 to 1200 persons, depending on the character of sand, character and strength of sewage and extent of preliminary treatment. For large treatment works, sand filtration has been virtually superseded by more intensive methods; but for small communities, especially where a high degree of purification is necessary, it still affords the best all-round method in a great many cases.

Contact beds consisting of shallow water-tight basins in which sewage is permitted to stand for an hour or two in contact with a relatively coarse material such as broken stone, coke or cinders, are, like intermittent sand filters, practically superseded by still more intensive treatment; but in special cases, particularly where odors near the treatment works must be avoided, they still have a valuable place. Where, for example, a highly purified effluent and

a strict avoidance of odors is demanded, contact beds for preliminary treatment may be effectively combined with intermittent sand filters. Contact beds four feet deep will handle satisfactorily the sewage from a population of 5,000 per acre.

1 Of all devices intended to produce a stable effluent, so-called sprinkling filters are in greatest favor at the present time. This device consists of a thoroughly underdrained bed of coarse material, five to nine feet in thickness, provided with means for spraying the sewage uniformly over the surface. With intelligent care and correct design this method is applicable to any size plant and is generally the cheapest to build for a given population contributing sewage from 15,000 persons in small plants and the sewage from 18,000 persons in large plants. As the effluent from such beds contains suspended matter, it is usually given a brief period of sedimentation before discharge into a water

course.

During recent years much attention has been given to preliminary treatment by screens and sedimentation tanks and to the so-called sludge problem. Fine screening and short periods of sedimentation are favored, as both produce a "fresh" effluent relatively free from odor and necessary for good results in filtration processes, yet they remove a substantial proportion of the suspended matters. Fine screening because of the more or less elaborate machinery required is best applicable to very large installations; while tanks possibly assisted by relatively coarse screening are best adapted to medium sizes and small installations. Where fine screens are used the solids may be pressed to free them of water and then burned under boilers or in specially constructed furnaces or it may be plowed under. Where sedimentation is used, the sludge is digested in separate digestion chambers in which it is permitted to rot thoroughly. The resulting product is relatively small in bulk, not offensive and may be easily dried on thin drainage beds of sand. The dried sludge has much the character of rich garden soil and may be disposed of on dumps or spread on lawns.

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