Treatment and reuse of domestic wastewater for irrigation and aquaculture purposes

The feasibility of sewage treatment via combined chemical-biological techniques has been investigated. Two-stages pilot plant were designed for this purpose. The first stage was direct chemical coagulation-sedimentation using ferric chloride in-combination with lime to reduce the organic load and to remove the colloidal and suspended solids. A comparison of two separation techniques namely chemical coagulation conventional sedimention and chemical coagulation tube settler sedimention were investigated. The second stage was either high rate oxidation pond or biological sand-bed to oxidize ammonia to nitrate. The results obtained showed that the effluent produced from the first stage is amaenable for restricted irrigation purposes. The HIROP proved to he satisfactory second treatment method for removal of pollutant. In addition high algal biomass was obtained. However, the use of sand-bed for nitrification proved to be more efficient, complete removal of ammonia was acheived. Average residual COD and BOD values were 66 and 38 mg O-2/L, respectively. Fish toxicity was completely eleminated after the nitrification processes.