Practical Methods of Sewage Disposal for Residences, Hotels and Institutions

by Henry N. Ogden; H. Burdett Cleveland

For many years it has seemed to thoughtful persons that permitting sewage, either from single houses or from larger communities, to be turned into streams was a mistaken policy because of the waste of manurial elements involved. It has long been understood that, in order to maintain the fertility of the soil, a constant application of fertilizers was necessary, and, while undoubtedly many farms are managed without any such repeated applications, the more scientific and modern farmer believes to-day that the frequent and abundant use of fertilizer is the foundation of his success.

In ordinary sewage there exists a certain amount of fertilizing elements. Two prominent English chemists, not many years ago, proved by their analyses that in ordinary sewage there existed the essential elements of a good fertilizer to the value of $2 per year for each person contributing to that sewage. Other chemists, working at the problem in other ways, have reached about the same result, and there can be little doubt of their accuracy if the fertilizing elements alone are considered. In applying these figures to the sewage of a city the difficulty has always been that the fertilizing elements have been so thoroughly covered up with the large volume of water present in the sewage that it has been practically impossible to separate them from the water. Thus, in a city of 100,000 persons, the fertilizer in the sewage might, indeed, be worth $200,000, but to realize this amount it must be separated from the 10,000,000 gallons of water—a task which is so tremendous, if not impossible, as to make the value of the fertilizer of no account. In those parts of the country where the water itself has a value, as in the irrigated lands of the West, the fertilizing elements of the sewage would be added to the value of the water, so that sewage used for irrigation would be worth not merely the value of the water alone, but also the value of the fertilizer present in that water.

Another difficulty in making use of the combined water and fertilizer is that the large amount of water involves a large area of land and suitable soil, on which irrigation may be practised, in the immediate vicinity of the city. This combination of agricultural soil of suitable texture at a suitable price for farming operations is so seldom found that this in itself usually precludes any application of the use of sewage for irrigation.

In the case of the sewage from a single house, however, the possibility of making use both of the water and the fertilizer in sewage is not so difficult. Recent writers on irrigation have pointed out that, while irrigation of late years has made most headway in the semi-arid districts of the West, there are many opportunities for its successful and profitable utilization in the East, and Mr. Lute Wilcox, in a recent book on irrigation, says: “The farmer who has a soil containing an abundance of all the needed elements in a proper state of fineness cannot but deem himself happy if he have always ready at hand the means of readily and cheaply supplying all the water needed by his soil and growing crops, just when and in just such quantities as are needed. Happier still may he be when he realizes that he need have no ‘off years’, and he knows that the waters he admits to his fields at will are freighted with rich fertilizing elements usually far more valuable to the growing crops than any that he can purchase and apply at a costly rate—a cost that makes serious inroads upon the profits of the majority of farmers cultivating the worn-out or deteriorated soils in the older States year by year. Fertilizers are already needed for the most profitable culture on many farms in Iowa, Minnesota, Eastern Kansas, and Nebraska, in Missouri, and in all States east of those named.”

Perhaps the greatest uncertainty in the matter of farming is the available water coming from the clouds. In one year the rainfall may come at the proper time to moisten the seed and to insure a rapid germination. These early rains may be followed by showers at proper intervals to supply the little rootlets with the necessary moisture so that the growth of the plant may be constant and vigorous. During the ripening season the rains may be withheld so that the harvest is insured under the most favorable conditions. In other years, however, the spring rains may be so continuous as to cause the seeds to rot, requiring a second sowing. Then the rains may fail so that the seeds either fail to germinate, or at best produce scattered and imperfect growths. At the time of harvest storm may follow storm, so that the harvesting of those plants which have developed is made almost impossible.

Irrigation tends in part to correct these difficulties, since it furnishes the soil with the needed water at times when the lack of rain would cause an entire failure in future growth. Irrigation, of course, cannot prevent rainfall, and it may be that after a copious soaking of the ground with the irrigating water a heavy rain may follow, resulting in an excess of moisture as bad for the ground as none at all. The possibility of irrigation cannot prevent excessive rains at the time of harvest, but the advantages of being able to control the soil moisture during the period of growth are more than enough to counterbalance any possible disadvantages. During the summer months evaporation is very high, the dryness of the air and the high temperature combining to draw moisture from the soil in considerable quantity. Then, too, the plants themselves, while absorbing moisture from their roots, evaporate moisture through their leaves, and agricultural stations have made extensive studies on the amount of this evaporation from different plants. The teaching of it all is that the amount of water which can be utilized by the soil, not merely for the sake of the growth of the plants themselves, but to make up for the demands of evaporation, is very high.

Mr. Newell, of the United States Geological Survey, points out that while the amount of water required for raising crops varies according to soil and other conditions, yet a large quantity is required to maintain the soil in such a degree of saturation as to best promote the vitality of the plant life. He shows that for each ton of hay raised upon an acre, from three hundred to five hundred tons of water must be furnished either by rainfall or by artificial means. In other words, since water covering an acre to a depth of one inch weighs about one hundred and thirteen tons, it would be necessary to cover an acre to a depth of from three to five inches if that acre produced one ton of hay. From actual conditions, he shows that it has been necessary, in order to produce five tons of barley hay per acre, to provide an amount of water which would cover the acre to a depth of twenty inches. Although his figures have special reference to the semi-arid regions of the West they furnish a guide for the amount of water which may profitably be used in addition to the rainfall, which, in the summer months, may be practically nothing even in the East. From three to six inches in depth each month is his estimate of the needed water for successful crop growing, the difference depending upon the character of the soil, more being required in sandy soils and less where the texture is finer.

The sewage from an ordinary household, on the basis of 30 gallons per head per day, amounts to 180 gallons per day, or about 5,400 gallons per month, or 720 cubic feet. This amount of water would cover an acre of ground to a depth of a little less than one-fourth of an inch, and it is plain that in order to have the sewage of a single house furnish the necessary amount of water for successful crop growing, the area required is only about one-twelfth of an acre, or an area about 60 feet square.

In the early days of the English experiments with the disposal of sewage, great stress was laid on the value of the manurial elements in sewage, and many tests were made as to the capacity of various soils for absorbing the moisture present in sewage. One of the most enthusiastic advocates of this method of disposing of sewage was Mr. J. Bailey Denton, who was able to act as engineer for many installations of various sorts. As a result of his experience he came to the conclusion that while the area depended upon the character of the soil, and while with the most suitable soil a very large amount of water might be taken care of, under ordinary conditions it was safest to so design the works that no possibility of overloading the soil with water could exist. He places the limits of population, the sewage from whom would be cared for on an acre, between 1,000 persons per acre and 100 persons per acre. More recent experience, together with constant observation of farms established in the early period of the practice, indicates that the higher value is too great, and that where agricultural processes alone are considered, 100 persons per acre is a suitable maximum value for irrigation on sandy loam, and that 40 persons per acre is a suitable number where the soil is inclined toward density and fine texture. Six persons in a household would, according to Mr. Denton, require from one-seventh to one-seventeenth of an acre. The amount, indicated by the computations made earlier, indicated one-twelfth of an acre for the same number of persons. The practical agreement of the two methods of computing the area necessary thus makes it possible to determine in either way the amount of land needed on a given farm for disposing of the household sewage.

The effect of sewage irrigation has been found to be most astonishing so far as the increased yield of the soil goes. Some years ago, in order to determine just the effect of the addition of sewage to ordinary farm land, a certain field of five acres was divided into four equal parts. The four fields were treated as follows: Field No. 1 received no sewage. Field No. 2 received six inches of sewage over its entire area on each of five successive months. Field No. 3 received twelve inches of sewage on each of five successive months. Field No. 4 received eighteen inches of sewage on each of five successive months. The following table shows the results of three successive years’ experiments at the sewage farm referred to at Rugby, England, the figures being the number of pounds of green grass cut from the fields.