Daily chemical variability of domestic septic tank effluent

Abstract

Effluent from the septic tanks of five households was sampled daily for 15 days. Temperature, redox potential, conductivity and biochemical oxygen demand (BOD5) were measured and samples were analyzed for N, P, Ca, Mg, Na, K, Zu, Zn, Cd, Cr, Pb, Mg, and linear alkylate sulphonate (LAS). Samples from the five households differed in the values obtained but the differences were small. Little daily variation occurred in the effluent from any one household. The effluent was in a reduced and anaerobic condition with almost all the N and P occurring in the inorganic form in solution. The effluent concentration N was about 100 mg l−1 and P concentration about 15 mg l−1. The mean annual N and P loading in the effluent over the five households was 3.8 kg N/head yr and 0.6 kg P/head · yr. Copper and Zn were the only trace metals of any significance and their concentrations were less than in tap water. The chemical composition of the effluent was very similar to that found in New Zealand, Canada, and U.S.A.