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 25similar to30 min/65similar to60 min in Tank 1, and 30similar to45 min/60similar to45 min in Tank 2, and a DO control set at 0.6similar to1 mg/L during the aeration period are required for satisfactory treatment performance. Under these conditions, a stable effluent water quality with BOD less than or equal to5 mg/L, CODMn less than or equal to8 mg/L, Nitrogen less than or equal to3 mgN/L, SS less than or equal to5 mg/L and transparency greater than or equal to80 cm can be achieved. The solids retention time in aerobic condition was 10similar to25 d, which is sufficient for nitrification.