N
2O is emitted through the wastewater treatment process, especially through biological nitrification and denitrification. Recently much attention has come to be paid to N
2O emission, because N
2O is one of the greenhouse effect gases, which is causing global warming. In this study, examination on the effectiveness of DO controlled intermittent aeration activated sludge process was made with respect to suppression of N
2O emission and improvement of nitrogen removal. The results obtained were as follows: DO control operation was superior to former timer control operation for the ability of both suppression of N
2O emission and nitrogen removal Judging from ORP in the aeration tank, DO control operation could change the surroundings in it periodically for the effective progress of nitrification and denitrification. At the pilot plant experiments, DO control operation was confirmed to be very effective way to suppress N
2O emission and to enhance nitrogen removal efficiency; The conversion ratio from removed nitrogen to N
2O-N was restrained to 0.05% and nitrogen removal efficiency reached over 80%. It was clarified that coagulant dosed and DO controlled intermittent aeration activated sludge process would be very promising way to prevent global warming and to improve water environment.
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