INFLUENCE OF MIXED LIQUOR RETURN RATIO ON DENITRIFYING PHOSPHORUS REMOVAL IN MODIFIED OXIDATION DITCH

Based on a laboratory scale oxidation ditch process acclimated with domestic wastewater as carbon source，the effect of mixed liquor reflux ratio on denitrifying phosphorus removal in the system was investigated at the mixed liquor reflux ratio of 100%，200% and 300%，respectively． The results showed that mixed liquor reflux ratio did not affect removal effect of TP， but affected the removal mode of TP under the experimental conditions． When the mixed liquid return ratio was 200% and 300%，most of the TP was removed in anoxic zone through the denitrifying phosphorus removal mode，and the mixed liquid return ratio was 100%，most of the TP was removed in aerobic zone． In general，with mixed liquid return ratio increasing，the removal rate of NH + 4 －N and TN were also increased． While the mixed liquid return ratio was 200%，the system obtained the highest nutrient removal efficiency with the removal rate of TP and TN reaching to 93. 9% and 82. 6% respectively，and NO－ 3 －N was sufficient in the anoxic zone as electron acceptor for denitrifying phosphorus removal． Taking both energy consumption and denitrifying phosphorus removal into consideration，the optimized mixed liquor return ratio of the process was 200%．