We have developed a new intermittently aerated anaerobic-aerobic activated sludge process. This process employs 2 reactors connected in series, and is capable of controlling the duration of aerobic, anoxic and anaerobic conditions in both reactors by utilizing the ORP bending point, which corresponds to the termination of denitrification. One cycle of aeration and agitation takes approximately 120 minutes. In the 1st reactor, nitrification and phosphorus uptake occur in the aeration period, followed by denitrification and phosphorus release in the agitation period. In the 2nd reactor, nitrification and phosphorus uptake are conducted during aeration, and denitrification and weak phosphorus uptake during agitation. A one-year pilot plant experiment using sewage (22 m3/day) showed stable and high removal ratios of 98% for BOD, 92% for T-N, and 85% for T-P under conditions of HRT 20 hours and water temperature 9∼33°C.

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