Using domestic sewage with low C/N as treatment objective

the performance of modified A2/O process for denitrification and phosphorus removal was investigated.In order to suitable allocation of carbon sources required by anaerobic phosphorus release and anoxic denitrification

raw water was distributed into anaerobic tank and anoxic tank according to different proportion.To stabilize nitrification and denitrification processes and improve their efficiency some packing was filled in aerobic and anoxic tanks whose effluent flowed into aerobic tank to reduce the sludge flow path.Under the optimal conditions:average influent COD/TN ratio 5.54

HRT 11 h

SRT 15 d

MLSS 3000—4000 mg·L-1

sludge reflux ratio 50%

the effect of inflow distribution ratio and internal reflux ratio on denitrification and phosphorus removal was investigated.The results showed that the optimal inflow distribution ratio was 5:5

at which iallocation of carbon source was reasonable for denitrification and phosphorous removal.And the optimal reflux ratio was 200%

if it is too high DO environment in anaerobic tank could be damaged and if it is too low the efficiency of denitrification in anoxic tank could not be full played.Under these optimal operating conditions

COD

NH3-N

TN and TP in effluent were 29.7 mg·L-1

0.1 mg·L-1

11.8 mg·L-1 and 0.42 mg·L-1 respectively

the average removal efficiency reached 87.8%

99.7%

72.4% and 91.3% respectively.The effluent could be better than the first level A of the discharging standard of pollutants for municipal wastewater treatment plant(WWTP)(GB 18918—2002).At the same time

in anoxic tank noteworthy denitrification and phosphorus removal were observed.