To obtain high-quality treated water without bulking activated sludge in the continuous or batchwise activated sludge process by stopping the treatment while leaving a specific amt. of BOD.
Most of the BOD(biochemical oxygen demand) related components easy to remove are removed by using a standard, completely-mixed, partition wall-provided, batchwise, air-diffused or mechanically-agitated activated sludge process device. In this case, to prevent bulking, i.e., to suppress the propagation of microorganisms in the filamentous form, the dissolved oxygen and nutrition are sufficiently balanced in an aeration tank, the excessive lowering of BOD in the supernatant which has been appropriately controlled in the aeration tank is avoided, and the treatment is stopped while leaving 60ppm BOD. Consequently, a high-quality treated water is obtained without bulking.
