A Pilot Study on the Volume Ratio of Anaerobic / Anoxic / Aerobic in A<sup>2</sup>/O Process Influence on Nitrogen and Phosphorus Removal

The volume ratio of anaerobic/anoxic/aerobic was an important factor for the removal of nitrogen and phosphorus in the A 2 /O process. A pilot plant of A 2 /O process was built in Xi’an to do the research about the influence on nitrogen and phosphorus removal when the volume ratio of anaerobic/anoxic/aerobic was changed. When the HRT was 10.1h and the volume rate of anaerobic/anoxic/aerobic was 1/1.7/2.4, the removal rate of COD didn’t raise substantially than that of normal volume ratio A 2 /O process, the removal rate average value of TN and phosphorus were 61.5% and 85.4% respectively. On this condition, the HRT in aerobic zone shorted to 4.7h, energy was saved about 33.8% in comparing with that of conventional volume ratio A 2 /O process.