By adjusting the distribution ratio of influent flow into anaerobic and anoxic zones

the removal efficiency of pollutants in low C/N(COD/total nitrogen)<3.5 municipal sewage using modified step feed process was analyzed. Keeping the following conditions unchanged: hydraulic retention time (HRT) 10 h

sludge retention time (SRT) 10—15 d

volume of anaerobic zone:volume of total anoxic zones:volume of total aerobic zones 4:9:9

when the actual efficiency obtained and material balance calculation results were utilized to increase gradually the water ratio distributing to the first stage i.e. anaerobic zone

the best operating conditions could be found and 4 kinds of operating conditions determined. The results show that

at given C/N ratio

concentration of nitrogen oxides in anaerobic zone does not decrease with the increase of the water ratio entered into anaerobic zone

even appears the opposite situation. The simultaneous nitrification and denitrification(SND)and microbial assimilation effect intensity play crucial role in TN removal. The rise of water ratio entered into anaerobic zone improves the removal rate of phosphate due to the phosphorus release effect of phosphorus-accumulating bacteria is enhanced in anaerobic zone. Both nitrogen and phosphorus removals as well as subsequent optimization space are considered

one of optimized water distribution ratio is 6:3:1

and at this condition

the effluent concentration of COD

ammonia nitrogen

TN

phosphate is 45.98

0.04

17.47 and 2.43 mg·L-1 respectively.