Post-treatment of septic tank effluents using intermittent sand filters operating under tropical conditions

Abstract

The objective of this research was to evaluate the performance of intermittent sand filters, septic tank effluent post-treatment operated under tropical conditions. The experimental system comprised a septic tank, subdivided into three chambers with longitudinal baffles incorporated into the first chambers and included an integrated balancing tank. This was followed by two intermittent sand filters which operated in parallel with surface area of 1.94 m2each. The depth of the sand in the filter was 1m and 2 filter, 0.5m. The filters were fed witn septic tank effluent through siphon system for 5 minutes every three hours (i.e. 8 cycles per day. The sanitary quality of final effluents and nitrification efficiency of the filters were monitored over a period of one year. Coliform removal efficiency was 3 thermo-tolerant log filter removal units 1 and 2 in the filter log 2 units, as the eggs of helminths removal was total. Ammonium nitrogen concentrations reduced from 34 mgNNH4+.L-1to 6.3 mg L-1and 5.6 mgN-NH4+ L-1respectively in the effluents of filters 1 and 2. This represented a decrease in ammonia concentration of ~81% for filter 1 effluent and ~83% for filter 2. Mean nitrate concentration in the effluent of filter 1 was approximately 28 mg NNO3-L-1and 35 mg N-NO3-L-1for filter 2.