Complete treatment of domestic sewage with a successive system of activated sludge and algal cultivation process

Abstract

The rice-washing water discharged from an institutional food service kitchen was found to show total COD of 7000-14000 mg/l, total kjeldahl-N of 400-600 mg/l, and total phosphorus of 200-300 mg/l. The high level pollutants were tried to remove by an activated sludge process in conjunction with an algal cultivation both in a bench-scale. The activated sludge process alone could reduce the initial COD of 1000 mg/l to 100mg/l, the initial nitrogen of 40 mg/l to 20 mg/l and the initial phosphate of 20 mg/l to 14 mg/l. Further reduction of these components in the activated sludge process effluent could be accomplished by culturing Chlorella cells in a specially designed cultivation chamber. Fortification of the effluent with a part of the activated sludge, a by-product of the previous stage, could enhance the reduction of nitrogen and phosphorus levels. The terminal effluent of the combined treatment system showed 120 mg/l COD, 15 mg/l Kjeldahl-N and 10 mg/l phosphate, which indicate 85.5\% reduction of initial COD, 70\% of nitrogen and 60\% of phosphorus in a continuous treatment. Easier system operation and less excess sludge volume, which have been thought as disadvantageous wastage in the secondary treatment process, were found in the system.