Nightsoil treatment plant converted into a sequencing batch reactor to improve removal of pollutants and nutrients

An existing 2 stage aerobic nightsoil treatment plant (25m(3)/d capacity) was converted (modified) from a conventional continuous flow system to a single stage SBR unit for nutrient removal. 10 months study indicated organic and nutrient removal drastically improved. Heat released from decomposition of high strength influent kept liquid temperature above 15 degrees C for a complete nitrification even during winter period. Nutrient removal efficiencies were found to be greatly affected by pH changes due to denitrification and nitrification. Increased pH due to denitrification stimulated chemical precipitation as struvite and hydroxyapatite. In contrast, decreased pH in aerobic stage due to nitrification dissolved the previously formed precipitates resulting in increase of PO4-P. Sludge fractionation indicated phosphorus was removed about 42% chemically and about 36% biologically. Piping changes and timer installations were the major capital investments in this modification, but energy savings were estimated to be about 40 to 53%. Additional savings in O&M could be expected from the improved effluent quality. Copyright (C) 1996 IAWQ.