ステップ流入二段嫌気好気活性汚泥法の最適運転方法に関する考察

Abstract

The four-stage denitrification-nitrification system with step-inlet was developed in order to prevent operational troubles in activated sludge plants, such as filamentous bulking, pH drop of the effluent because of advanced nitrification, and so on. Pilot-scale treatment experiments using municipal wastewater were conducted to clear the treatment characteristic and the optimum operating condition of this process.The equations were introduced to simulate microbial behavior in this process based on population dynamics. Then, the coefficients of these equations were determined by the results of pilot-scale treatment experiments and some reference, and it was revealed that the simulated water qualities in the reactor agreed with the results of pilot-scale treatment experiments. The simulation results suggested that this process is more suitable than the conventional activated sludge process to prevent the filamentous bulking and pH drop of the effluent because of advanced nitrification, within wide operation range of primary settling tanks. The nitrification-suppressed operation was more effective than the nitrification-enhanced operation to prevent the filamentous bulking, also, the shorter solids retention time (SRT) was effective to prevent it.The four-stage denitrification-nitrification process with step-inlet can also prevent the filamentous bulking, if nitrification-suppressed or nitrification-enhanced operation was switched according to the nitrification activity with wide range of water temperature.