Short-term effects of excessive anaerobic reaction time on anaerobic metabolism of denitrifying polyphosphate-accumulating organisms linked to phosphorus removal and N2O production

Abstract

The short-term effect of anaerobic reaction time (AnRT) (i.e., 90, 120 and 150 min) on the denitrifying phosphorus (P) removal performance and N2O production was examined using a denitrifying enhanced biologic phosphorus removal (EBPR) sludge acclimatized with mixed acetate (HAc) and propionate (Pro) (in the molar ratio 3:1) as carbon sources. The results showed that when the AnRT was prolonged from 90 to 150 min, the anaerobic polyhydroxyalkanoate (PHA) synthesis was decreased by 15.3%. Moreover, the ineffective PHA consumption occurred in anaerobic phases and contributed to an increased NO2−-N accumulation and higher free nitrous acid (FNA) concentrations (⩾0.001–0.0011 mg HNO2-N/L) in the subsequent anoxic phases, causing a severe inhibition on anoxic P-uptake and denitrification. Accordingly, the total nitrogen (TN) and total phosphorus (TP) removal efficiencies dropped by approximately 6.3% and 85.5%, respectively; and the ratio of anoxic N2O-N production to TN removal increased by approximately 3.8%. The fluorescence in situ hybridization (FISH) analysis revealed that the sludge was mainly dominated by Accumulibacter (62.0% (SEmean = 1.5%)). In conclusion, the short-term excessive anaerobic reaction time negatively impacted denitrifying P removal performance and stimulated more N2O production, and its effect on P removal was more obvious than that on nitrogen removal.