Rural Hygiene

by Henry N. Ogden

CHAPTER X

SEWAGE DISPOSAL

The subject of sewage disposal for a single house in the country does not at all present the elaborate problem that is suggested when the disposal of sewage of a city is under discussion. In the first place, the amount of sewage to be dealt with is moderate in quantity; and in the second place the area available on which the sewage may be treated is in almost all cases more than ample for the purpose. Nor is there the complication that arises with city sewage, due to the admixture of manufacturing wastes. The material to be handled is entirely domestic sewage and varies only according to the amount of water used in the house, making the sewage of greater or less strength according as less or more water is used. Sewage from a single house differs only in one respect disadvantageously from city sewage, namely, in the fact that the sewage, not having to pass through a long length of pipe, comes to the place of disposal in what is known as a fresh condition; that is, no organic changes have taken place in the material of which the sewage is composed.

Definition of sewage.

The great bulk of sewage is water, and, in quantity, the amount of sewage to be cared for is about equal to the amount of water consumed in the household, although this will depend somewhat on the habits of the family. If, for example, part of the water-supply is used for an ornamental fountain in the front yard, or if in the summer time a large amount of water is used for sprinkling the lawns, that water is not converted into sewage, and the amount of the latter is thereby diminished; but, ordinarily, it is safe to say that the quantity of water supplied to the house and the quantity of sewage taken away from the house is identical, and since it is much easier to measure the water-supply than the sewage flow, the former is taken as the quantity of sewage to be treated.

In the course of its passage through the house, however, the water has added to it a certain amount of polluting substances, largely derived from the kitchen sink, where dirt from vegetables and particles of vegetable material, together with more or less soap, are carried by the waste water from the sink into the drain. In the bath-room, also, some small amount of organic matter is added to the water, but the proportion of such matter to the total volume of water used is very small, probably not exceeding one tenth of one per cent. This small proportion is nevertheless sufficient to become very objectionable if allowed to decompose, and the problem of sewage disposal for a single house is to drain away the water, leaving behind the solids so disposed that they shall not subsequently cause offense by their putrefaction.

The process of decay is normal for all organic matter and is due to the agency of certain bacteria whose duty it is, providentially, to eliminate from the surface of the earth organic matter which otherwise would remain useless, if not destructive, to man. It is impossible to leave any vegetable or animal matter exposed to the air without this process of decay at once setting in. Apples left in the orchard at the end of the season inevitably are reduced and disappear in a short time. Dead animals, whether large or small, in the same way succumb to the same process of nature, and it has been pointed out that, unless this provision did exist, the accumulation of such organic wastes since the settlement of this country would be so great as to make the country uninhabitable. Fortunately, however, this inevitable process breaks down the structure of all organic material, partly converting fiber and pulp into gas, partly liquefying the material and converting the remainder into inorganic matter which is of vast importance as food for plant life. A cycle is thus formed which may be best illustrated in the case of cows which feed on the herbage of a meadow, the manure from the cows furnishing food for the grass which otherwise would soon exhaust the nutriment of the soil.

Stream pollution.

The first fundamental principle of sewage disposal, therefore, is to distribute the organic matter in the sewage so that these beneficent bacteria may most rapidly and thoroughly accomplish their purpose. During the last fifty years, a great deal of study has been expended on this problem, and while it has not as yet been entirely solved, certain essential features have been well established.

The most important factor promoting the activity of these agents of decay is the presence of air, since in many ways it has been proved that without air their action is impossible. Thus it has been shown that discharging sewage into a stream, whether the stream be a slow and sluggish one or whether it be a mountain stream churned into foam by repeated waterfalls, has little other power to act on organic matter than to hold it for transportation down stream, or to allow it to settle in slower reaches until mud banks have been accumulated which will be washed out again at the first freshet. Experiments have shown that the agencies to which certain diseases are attributed, commonly known as pathogenic bacteria, are frequently, if not always, found in sewage, and that when these bacteria are discharged into streams they may be carried with the stream hundreds of miles and retain all their power for evil, in case the water is used for drinking purposes. No right-minded person to-day will so abuse the rights of his fellow-citizens as deliberately to pour into a stream such unmistakable poison as sewage has proved itself to be. The fact is so well known that it is not worth while pointing out examples. It is enough to say that some of the worst epidemics of typhoid fever which this country has known have been traced to the agency of drinking water, polluted miles away by a relatively small amount of sewage.