Ground Water Recharge with Sewage Effluent

Abstract

Sewage effluent is an excellent source of water for irrigation, especially in dry areas. Before it can be used for unrestricted irrigation, conventional treatment should be followed by treatment so that the water meets the agronomic, public health, and aesthetic requirements for unrestricted irrigation. This usually means reduction of nitrogen concentration to less than 10 mg/l, complete removal of pathogenic organisms, and essentially complete removal of suspended solids and biodegradable organic carbon. This can often be achieved with a groundwater recharge system, using the soil and aquifer materials as natural filters. Studies on two experimental projects in Phoenix showed that “soil-aquifer treatment” systems can reduce nitrogen concentrations from about 20 mg/l to about 7 mg/l, fecal coliform concentrations from about 3500 per 100 ml (chlorinated secondary effluent) to 0.3 per 100 ml, viruses from 21 plaque-forming units/l to 0, suspended solids from 15 mg/l to 1 mg/l, and total organic carbon from 20 mg/l to 3 mg/l. The latter represents mostly the nondegradable carbon. Hydraulic loading rates for sands to loamy sands were about 300 ft/yr. Thus, 1 acre of infiltration basin can renovate about 300 af/year of sewage effluent. The renovated water should be removed from the aquifer to avoid its spread into high-quality native groundwater.(Please note that af/year stands for acre feet/year.)