Sewerage and Sewage Treatment

by Harold E. Babbitt

Irrigation

260. The Process.—Broad irrigation is the discharge of sewage upon the surface of the ground, from which a part of the sewage evaporates and through which the remainder percolates, ultimately to escape in surface drainage channels. Sewage farming is broad irrigation practiced with the object of raising crops. Broad irrigation can be accomplished successfully without the growing of crops, but it is seldom attempted as some return and sometimes even a profit can be obtained from the crops raised. Broad irrigation and sewage farming differ from intermittent sand filtration in the intensity of the application of the sewage, the method of preparing the area on which the sewage is to be treated, and the care in operation. In broad irrigation and intermittent sand filtration the paramount consideration is successful disposal of the sewage. In sewage farming the paramount consideration is the growing of crops. The growing of crops may be combined with irrigation and filtration, however, but the crop should be sacrificed to the successful disposal of the sewage.

The change which occurs in the characteristics of the sewage due to its filtration through the ground is the same as occurs in aërobic filtration. The effect on the crops is mainly that of an irrigant, as the manurial value of the sewage is small.

261. Status.—The disposal of sewage by broad irrigation was practiced in England previous to the development of any of the more intensive biologic methods of treatment. It was considered the only safe and sanitary method for the disposal of sewage, and as a result, areas irrigated by sewage were common throughout England. Crops were grown on these areas as a minor consideration, and sewage farming gained some of its popularity from the apparent success of these disposal areas. The success of sewage farms is due more to generous irrigation in dry years than to fertilization by sewage.

The sewage farms of Paris and Berlin are frequently cited as examples of the successful and remunerative disposal of sewage by farming in connection with broad irrigation. Kinnicutt, Winslow, and Pratt[^[169]] state:

The Berlin Sewage farms offer examples of broad irrigation under better conditions ... of 21,008 acres receiving sewage, 16,657 acres were farmed by the city, 3,956 acres were leased to farmers, and only 395 acres were unproductive. The contributing population at this time was 2,064,000 and the average amount of sewage treated was 77,000,000 gallons, giving a daily rate of treatment of about 3,700 gallons per acre of prepared land. The soil is sandy and of excellent quality. A quarter of the area operated by the authorities is devoted to pasturage, and about a third to the cultivation of cereals, of which winter rye and oats are the most important. Potatoes and beets are grown in considerable amounts and a wide variety of other crops in smaller proportions.... Even fish ponds are made to yield a part of the revenue, and the drains on some of the farms have been successfully stocked with breed trout.

The cost of the Berlin farms to March 31, 1910, was $17,470,000, somewhat more than half being the purchase price of the land. The expenses for this year amounted to $1,300,385 for maintenance, and $741,818 for interest charges. The receipts were $1,240,773 and there was an estimated increase of $122,593 in value of live stock and other property.

The conditions at Berlin are quoted at length to indicate the success which can accompany broad irrigation, and as an example of what is being done abroad, where the rainfall is light and the soil is suitable.

In the United States success in sewage farming has not been marked. This may be due partially to the relative weakness of American sewages, to the cost of labor, to lack of satisfactory irrigation areas, and to inattention to details. An attempt was made to grow crops on the sand filters at Brockton, Mass., but it was finally abandoned as the interests of the crops and the successful treatment of the sewage could not both be satisfied. At Pullman, Illinois,[^[170]] in 1880, there was commenced probably the most extensive attempt at sewage farming in eastern United States. The farm was a failure from the start, because of the clay soil, and it was subsequently abandoned. Sewage farming, mainly as a subsidiary consideration to the filtration of sewage, is practiced in a few cities in the eastern portion of the United States to-day. Among the cities mentioned by Metcalf and Eddy[^[171]] are Danbury, Conn., and Fostoria, Ohio. In the western portion of the United States where water is scarce and the ground is porous, sewage has been used as an irrigant with some success. Such use of sewage cannot be considered as a method of treatment since the prime consideration is the growing of crops. In this process all sewage not used as an irrigant is discharged without treatment into water courses. According to Metcalf and Eddy there were 35 cities in California in 1914 that were operating sewage farms. Among these are Pasadena, Fresno, and Pomona. Other farms, notably the pioneer farm at Cheyenne, Wyo., have been abandoned because of the local nuisance created and the lack of financial success.

262. Preparation and Operation.—A porous sandy soil on a good slope and with good underdrainage is most suitable for broad irrigation. Impervious clay or gumbo soils are unsuitable and should not be used. They become clogged at the surface, forming pools of putrefying sewage, or in hot weather form cracks which may permit untreated sewage to escape into the underdrains.