The effect of poly-β-hydroxyalkanoates degradation rate on nitrous oxide production in a denitrifying phosphorus removal system

•N2O production in denitrifying phosphorus removal process was studied.•The decrease of PHAs degradation rate did not cause an increase in N2O production.•The electrons distributed to nitrite reductase were 1.6 times of that to N2O reductase.•Controlling nitrate supply rate via continuous feed could reduce N2O production.

Poly-β-hydroxyalkanoates (PHAs) and free nitrous acid (FNA) have been revealed as significant factors causing nitrous oxide (N2O) production in denitrifying phosphorus removal systems. In this study, the effect of PHA degradation rate on N2O production was studied at low FNA levels. N2O production always maintained at approximately 40% of the amount of nitrite reduced independent of the PHA degradation rate. The electrons distributed to nitrite reduction were 1.6 times that to N2O reduction. This indicated that electron competition between these two steps was not affected by the PHA degradation rate. Continuous feed of nitrate was proposed, and demonstrated to reduce N2O accumulation by 75%. While being kept low, a possible compounding effect of a low-level FNA could not be ruled out. The sludge used likely contained both polyphosphate- and glycogen-accumulating organisms, and the results could not be simply attributed to either group of organisms.