PART II. SEWAGE DISPOSAL

ART. 63.

CHAPTER XIV

DISPOSAL BY DILUTION

"DISPOSAL AND "SEWAGE " DEFINED

THE word disposal is often used where treatment would more properly be employed. As a matter of fact all sewage, dry or water-carried, must be disposed of in some way after having been collected by a sewerage system. But if this disposal consists of anything other than throwing away the sewage this may be properly called a treatment thereof. These words will be used thus in this work-disposal as a general term, treatment as a more specific one.

For a proper consideration of the various methods of disposal it will be necessary to understand the results aimed at and the principles involved. And first we must understand what is implied by the word sewage. Sewage may be found to contain almost every description of waste matter: fæces, house-" slops," manufacturing waste-waters and acids, drainage of stables, piggeries and slaughter-houses, waste paper and rags, and frequently garbage, and numberless matters which should never reach the sewer. This is ordinarily called house sewage. Into combined and storm sewers, besides rainwater, not only horse-droppings and vegetable refuse but sand, clay, gravel, and other heavy matters find admission through the street inlets. These go to make what is called storm sewage. The common impression is that, of these, human excrements alone are dangerous; and this is to a large extent true so far as concerns dissemination of the germs of disease. But it is known

that, aside from this, kitchen-wastes are fully as objectionable, since they contain practically the same putrescible matter, and in a state less easily rendered innocuous by either natural or artificial means. Where storm-water is admitted to the sewers, the large quantities of horse-droppings which are washed in during the first few minutes of each rainstorm render the water during that time nearly as offensive, if not so dangerous, as do human excreta.

Owing to diversity of manufacturing industries, to differences in the characters of the water used by different towns, and to other local peculiarities, the sewage of each town varies from that of almost every other. Therefore the question of the proper disposal of this compound is seen to be a problem of no easy solution. The difficulty of treatment is increased by the exceeding dilution of the sewage, since the sewage of an average American town will contain less than 1 part in 1000 of organic matter, I part of mineral matter, and 998 to 999 parts of water.

ART. 64. AIMS OF DISPOSAL

The first aim is the getting rid of the sewage; the disposing of it in such a way and such a place that it will not create a nuisance. Communities, being even more selfish than individuals, seldom regard the well-being of other communities, but are satisfied if no nuisance is created within their own limits. It is here that the State, by its laws and through its Board of Health, should interfere for the protection of each community against all others. In England this protection is afforded by national laws and a national board. In this country a number of States within the past few years have enacted laws affording a certain amount of such protection. The first of these was Massachusetts, but Pennsylvania, New Jersey, New York, and Ohio now have excellent laws and most of the other States are falling into line. It is a duty which the engineer owes to humanity to educate the people to the importance of this matter; though he will often be compelled to yield, in part at least, to the selfish demands of those for whom he acts that they

be put to no expense for protection of other communities that is not required by State or national laws.

When this protection is afforded through adequate laws properly enforced, the disposal of the sewage must be such that it will "lose permanently its power for evil." How this can best and most economically be done is the question to be solved.

Many attempts have been made at a solution of this question of disposal that shall not only meet the sanitary requirements, but that shall also be financially remunerative. Some reports of success have been heard of, but when investigated the details are found to be disappointing, and the author knows of no case where the disposal of sewage is accomplished at a profit to the city or town. This is not to be wondered at, since the value of the manure contained in one ton of Boston's sewage, for instance, is estimated to be but one cent.

The sewage of several of our Western cities situated in the "desert" region is disposed of for irrigation at a considerable profit. But in general few, if any, farms in districts where irrigation is not necessary, and on which sewage must be turned in rainy as well as in dry weather, will bring any considerable rental; and no other system of treatment is known which will return any net profit above running expenses, although there is a possibility of such result being obtained by the "activated sludge" process. Until a financially profitable process available, the endeavor should be to find for each place that method of disposal which, under the existing conditions of location, character of sewage, etc., will best meet the requirements both of the State laws and of the laws of sanitary science, and which will be least expensive, both first cost and maintenance being considered.

ART. 65. PRINCIPLES INVOLVED

For an exposition of the principles involved we must call upon chemistry, biology, bacteriology, medicine, and kindred sciences. Their teachings, stated generally, are:

That matter in a state of putrescence is harmful to human life if taken into the system.

That volatile emanations from such matter, when breathed continually into the lungs, probably lower the tone of the constitution but do not directly occasion disease.

That many diseases may be contracted by taking into the stomach certain germs which are found to be excreted by those already sick of such a disease, and these germs will exist for days in sewage having any amount of dilution.

That ordinarily excreta do not putresce until from twentyfour to sixty hours after their discharge, or even longer under certain circumstances, such as absence of moisture.

That the only true destruction of the dangerous characteristics of sewage is that effected by oxidation, which transforms the putrescible organic matter into harmless mineral compounds, and by removal of the disease germs.

The legal principles involved vary in different localities and with different interpreters of the law, frequently depending upon the ruling as to what creates a nuisance. A recent ruling in the United States has included in the "creating of a nuisance" the rendering unfit for drinking purposes of water which would otherwise be used thus. Under properly prepared State laws, interference with the health and rights of others should be preventable by injunction, or, in the case of injury to private interests, should subject the city to forfeiture of damages. The Supreme Court of Connecticut has held that: "The discharge of sewage and other noxious matters into an inland stream to the injury of a riparian proprietor below has been held to be an unlawful invasion of the rights of said proprietor, remediable by injunction, by the courts of nearly every State, by the federal courts, and by the courts of England." (Morgan et al. vs. City of Danbury, Conn.)

Most of the states now have laws, more or less rigidly enforced, requiring sewage to be partially purified before being discharged into any stream, provided such treatment is ordered by the State Board of Health or similar state authority; the degree of purification to be satisfactory to such authority. Therefore, in

each case the State laws on this point must be learned, and, when these require it, the state health authority consulted to learn whether treatment will be required.

From a sanitary and engineering, rather than a legal standpoint, it is a mooted question, concerning which sanitarians as well as city officials and engineers disagree, as to how much purification it is proper to require of cities and of private individuals who discharge sewage and other poliuted water into streams. It is theoretically possible, but hardly practicably so, for sewage to be transformed into clear and practically harmless drinking water, but this would be very expensive in the majority of cases. At very much less expense sewage can be so freed of organic matters that there will be little or no danger of its creating a nuisance after being discharged into a stream on tidal water; the amount of purification required depending to a considerable degree upon the amount and character of the water which receives the effluent. It is also possible to almost entirely sterilize a sewage effluent after removing the grosser impurities. In the great majority of cases the effluent should be such as will, after discharge into the steam which receives it, create no nuiWhere it is discharged into a large body of salt water where tides and currents will remove it from the neighborhood of the land, it may be that no purification whatever will be needed. (But in this case the possibility of shoaling of channels by deposits should be borne in mind.) Where there are shellfish reached by the effluent, it is generally considered that practical sterilization is desirable.

sance.

In the case of fresh-water streams, even those which may be drawn upon for water supplies lower down, there is considerable difference of opinion. Some maintain that effluents reaching these should be freed from all putrescible organic matter and also be practically sterile. Others, however, claim that cities or private companies desiring to use the water for drinking supplies can make such supplies safe only by purification, even though it receive no sewage, since other sources of pollution remain which it is almost impracticable to eliminate; and that this being the case, it would cost little if any more to effect the purification