Experimental Study On Two-stage A/O Process For Domestic Sewage Treatment

Presently, the A2/O (Anaerobic-Anoxic-Oxic) process is one of the mainstream processes of biological nitrogen and phosphorus removal. This process is widely applied in wastewater treatment for simple flow, easy operation and management. However, there are contradictions of carbon resource, nitrate, SRT and so on, the effect of the nitrogen and phosphorus removal is difficult to be raised in the same time.Two different types of microbe fulfill the nitrogen and phosphorus removal, and the microbe requirements of environmental factors are different. The two-stage A/O process is presented from the aspect of solving the SRT contradict to improve the traditional A2/O process. The character of this process is to divide the nitrogen and phosphorus removal process into two fore-and-aft A/O processes, respectively. Phosporus is removed in the first A/O process, which the activated sludge method is used. Nitrogen is removed in the second A/O process, which bio-film method is used. The space division of PAOs, denitrifying bacteria and nitrifying bacteria is realized, and the SRT contradict is solved. Therefore the nitrate by nitrification in the second stage A/O does not flow into the first stage and influence phosphorus removal process, the problem of the nitrate disturbance is solved.The two-stage A/O process apparatus is operated in six working conditions, and researches on phosphorus removal in normal temperature and nitrate removal in low temperature using the domestic sewage.When the SRT is 6 days and the water temperature is 22~28℃, the average concentration of ammonic nitrogen in the effluent is 5.9 mg/L, and the removal rate is 82.5%. The concentration of TP is 1.0 mg/L, and the removal rate is 69.7%. COD is 40mg/L, and the removal rate is 83.1%, which meets the first class in national effluent standard GB18918-2002. When the wastewater is lower temperature condition, such as in winter, the system is effective in removal COD and TP.The total nitrogen removal rate is only 30.4%, because the C/N rate is low in the raw water. However, the first stage A/O process consumes the large part of carbon resource, leading to the lack of denitrifying carbon resource in the second stage A/O process. In winter, the nitrifying rate is lower than summer. Ammonic nitrogen in the effluent is 30.4mg/L, and the average removal rate is 11.8%. It indicates that the lower temperature can apparently retrain nitrifying process.Based on the two-stage A/O process, the bio-film methed is used in the second stage A/O, which is the character of this experiment process. This research is profitable on the biological nitrogen and phosphorus removal for domestic sewage, and provides a new idea of raising the effect of the biological nitrogen and phosphorus removal.