Treatment of low turbidity micro-polluted water by combination process of preoxidation and sludge return

A process of potassium permanganate preoxidation combined with sludge return was applied to treat the low turbidity,micro-polluted raw water.The results showed that the turbidity of settled water could effectively be improved when the optimal sludge return ratio was 60%,and the turbidity of settled water decreased from 1.91 NTU to 1.51 NTU with the sludge return.Meanwhile the removal of organic matters could be improved by return of powdered activated carbon with sludge.The efficiency could be further improved by dosing potassium permanganate.The efficiency of coagulation and turbidity removal could be enhanced by sludge return,therefore the removal of organic matters was significant.