Abstract
This study was carried out to investigate change in influent concentration of domestic wastewater flowed from a newly constructed separate sewer system (SSS) and biological nutrients removal efficiency of a full scale Air-vent sequential batch reactor (SBR, $600m^3/d$). The average concentration of $BOD_5$, SS, T-N and T-P from SSS were 246.5 mg/L, 231.6 mg/L, 42.974 mg/L, 5.360 mg/L, respectively which corresponds to 2.2times, 1.2times, 1.8times and 2.1times higher than those from the conventional combined sewer system (CSS). The removal efficiency of $BOD_5$, SS, T-N, and T-P for the Air-vent SBR operated with influent from SSS averaged 99.1%, 99.0%, 91.2%, and 93.5%, respectively. Especially the respective nitrogen and phosphorus removal was 15% greater than that of the SBR operated with influent from CSS. Simultaneous nitrification and denitrification (SND) was observed in an aerobic reactor(II) as a result of DO concentration gradient developed along the depth by the Air-vent system. In order to achieve T-N removal greater than 90%, the C/N ratio should be over 6.0 and the difference between $BOD_5$ loading and nitrogen loading rate be over 100 kg/day (0.130 kg $T-N/m^3{\cdot}d$). Even with high influent T-P concentration of 5.360 mg/L from SSS (compared with 2.465 mg/L from CSS) T-P removal achieved 93.5% which was 15.5% higher than that of the SBR with influent from CSS. This is probably due to high influent $BOD_5$ concentration from SSS that could provide soluble carbon source to release phosphorus at anaerobic condition. In order to achieve T-P removal greater than 90%, the difference between $BOD_5$ loading and phosphorus loading rate should be over 100 kg /day (0.130 kg $T-N/m^3{\cdot}d$).
