[Competition and optimization of AOB and NOB for domestic wastewater treatment at normal temperatures]

At normal temperature of 19 degrees C +/- 1 degree C and seed sludge from the system of conventional nitrogen removal via nitrate composed of both ammonia oxidizing bacteria (AOB) and nitrite oxidizing bacteria (NOB), the competition and optimization of AOB and NOB was investigated in a lab-scale SBR treating domestic wastewater. The reactor was operated under the aeration rate of 40 L/h with the average DO concentration below 1.0 mg/L, and combined with the control of aeration time, i.e., aeration was stopped before the pH "ammonia valley" was detected. After AOB became pre-dominant nitrifying bacteria (nitrite accumulation rate NO2(-)-N/NOx(-)-N reached 50%), the aerobic durations were gradually prolonged from 3 h to 4 h and 5 h to improve the ammonia removal efficiencies and enhance AOB dominant. By the above operational pattern, nitrogen removal via nitrite was successfully achieved with NO2(-)-N/NOx(-)-N over 95%. Fluorescence in-situ hybridization (FISH) analysis showed that AOB was accounted for 9.97% of total biomass. The on-line control of aerobic duration was an effective method to maintain the partial nitrification and the NH4(+)-N removal efficiency was above 97%. The research results also proved that at normal temperatures, for the seed sludge from the conventional nitrogen removal via nitrate, AOB would not become dominant nitrifying bacteria only by the aeration time control without the DO restriction.