Effect of dissolved oxygen conditions on nitrogen removal in continuously fed intermittent-aeration process with two tanks.

In this study, an intermittent aeration type activated sludge process that is fed continuously is evaluated for nitrogen and organic carbon for facilities in rural areas, which are characterized by small scale, low loading rate and automatic operation. Anoxic and aerobic conditions can be regulated alternatively by intermittent aeration for biological nitrogen removal. It is proved that an intermittent aeration cycle of 90 min, with aeration/anoxic mixing periods of 25-30 min/65-60 min in Tank 1, and 30-45 min/60-45 min in Tank 2, and a DO control set at 0.6-1 mg/L during the aeration period are required for satisfactory treatment performance. Under these conditions, a stable effluent water quality with BOD < or = 5 mg/L, CODMn < or = 8 mg/L, Nitrogen < or = 3 mgN/L, SS < or = 5 mg/L and transparency > or = 80 cm can be achieved. The solids retention time in aerobic condition was 10-25 d, which is sufficient for nitrification.