Bioremediation of pit toilet sewage

Abstract

The paper examines the efficacy of anaerobic, aerobic and denitrification reactions in reducing organic carbon (C), ammonium and nitrate concentrations in pit toilet sewage. The anaerobic character of pit toilet sewage causes nitrogen (N) to prevail as ammonium rather than as nitrate ions. Anaerobic decomposition of organic carbon is initially resorted to reduce competition for ammonium oxidation during subsequent aerobic treatment of sewage. A mixture of air-dried cattle manure, sand and gravel is used as a biobarrier medium for nitrate reduction. Cattle manure serves as an affordable organic carbon source; sand particles act as a medium for attached bacterial growth, while gravel improves the permeability of the barrier. Batch tests showed that anaerobic reactions reduce chemical oxygen demand (COD) concentration in pit toilet sewage by 85%. Comparatively, aerobic reactions reduce ammonium concentration in sewage by 77% through assimilation, nitrification and adsorption; 6–10 h of contact between the biobarrier mix and nitrate leads to acceptable levels of denitrification (residual nitrate concentration < 45 mg/l). A modified twin-pit toilet that facilitates anaerobic decomposition of sewage in the first pit and aerobic treatment and denitrification of sewage in the second pit is constructed at Mulbagal town, Karnataka, India.