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 capaci ty) was converted (modified) from a conventional continuous flow syste m to a single stage SBR unit for nutrient removal. 10 months study ind icated organic and nutrient removal drastically improved. Heat release d from decomposition of high strength influent kept liquid temperature above 15 degrees C for a complete nitrification even during winter pe riod. Nutrient removal efficiencies were found to be greatly affected by pH changes due to denitrification and nitrification. Increased pH d ue to denitrification stimulated chemical precipitation as struvite an d hydroxyapatite. In contrast, decreased pH in aerobic stage due to ni trification dissolved the previously formed precipitates resulting in increase of PO4-P. Sludge fractionation indicated phosphorus was remov ed about 42% chemically and about 36% biologically. Piping changes and timer installations were the major capital investments in this modifi cation, but energy savings were estimated to be about 40 to 53%. Addit ional savings in O&M could be expected from the improved effluent qual ity. Copyright (C) 1996 IAWQ.