Abstract
Reduction of activated sludge by using Aqua-ball, which was made from oyster shell powder and harden to 4cm ball type by incineration, was examined. The 4－l scale activated sludge treatment system set up using artificial sewage was used for experiment under completely mixed condition. When 8 pieces of Aqua-ball was added into the aeration vessel, about 25％ reduction of MLSS was observed at steady state of continuous treatment compared with that of control experiments. At this time, respiration quotient of sludge increased and proportion of aerobically grown bacteria increased. Same phenomena were observed when oyster shell powder or and oyster shell extract was added. Therefore, it was suggested that some component(s) of oyster shell promoted the growth of aerobically grown bacteria. As a result, CO2 exhaust is expected to increase followed by the reduction of activated sludge.
