Design and Management of Sewage Farms | Sewage Disposal | Sanitary Engineering

In this article we will discuss about the design and management of sewage farms.  

The sewage should be used to its optimum limit for the irrigation purpose. Optimum utilisation means full and judicious use of sewage components viz., water, plant and nutrients and organic matter in the sewage farms.

Following points must be kept in view while utilizing the sewage for farming:

(a) The pathogenic infection should not spread among the farm workers nor the consumers of sewage farm products.

(b) The ground water should not be contaminated.

(c) None of the three main components of sewage are wasted.

(d) There should not be any deterioration of the soil properties.

The main principle of the irrigation management to irrigate the fields only when it is required by the crop. The water requirement of the crops depends on the type of soil, the crop and the climate of the area. Table 11.9 gives the water requirement of some soils to wet them to a depth of 30 cm.

Table 11.10 gives the water requirement of various crops. Water requirements of crops vary with the duration of their growing season and the amount of growth in unit time.

The irrigation requirement of any crop is not uniform throughout its growing period. It varies with the stage of growth. Water requirement of crop at different growth stages can be determined either directly or indirectly by use of Tensiometers or Irrometers or gypsum blocks.

Usually when there is about 50% depletion of available moisture in the soil, irrigation should be done. As the crop plants themselves show sign of moisture stress, one should look out for such first symptoms requiring irrigation. The extent of irrigation depends on the depth of irrigation to be provided and volume of water required for wetting the soil up to required depth.

Table 11.11 gives the recommended hydraulic loadings of settled sewage for different types of soils.

If the farms are using settled sewage, the sludge from the sedimentation tanks should be mixed with manure or peat and composted for which adequate land should be provided. The duration of composting should be so chosen as to ensure complete dehelminthization of the sludge. The composted material is applied on fallen fields or in the farm itself.