Effect of dissolved oxygen on removal of nitrogen and phosphorus in Biolak/A~2O process

A full-scale Biolak /A2 O process was studied to treat domestic wastewater.The effect of dissolved oxygen(DO) in oxic zone on removal of nitrogen and phosphorus in the system was investigated.The results indicated that the variation of DO concentration has no significant effect on the removal of COD and NH+4-N.However the nitrogen and phosphorus removal efficiency in the system is significantly affected by the DO concentration.By controlling DO at 0.80 ~ 1.50 mg·L-1,the treatment efficiency of system is near optimal with the total nitrogen efficiency of 69.5%.The simultaneous nitrification and denitrification can be achieved under this condition.Based on the calculation equations and transformation pathways of nutrients,about 23.7% of total nitrogen(TN) was removed by multistage A /O system in the oxic tank.When DO is 1.00 ~ 3.00 mg·L-1,the total phosphorus(TP) removal efficiency reaches the maximum at 74.0%.DO in the range of 1.00 ~ 1.50 mg·L-1is optimal for removal of nutrient in Biolak /A2 O process,with removal efficiency of TN and TP of 68.9% and 73.7%,respectively.TN and TP of the effluent are 12.02 mg·L-1and 0.95 mg·L-1,respectively.