The behavior of the DNPAOs at the anaerobic-anoxic process according to the change of the influent NO3−−N loading

Abstract

This study was conducted to investigate the ratios of phosphorus release to COD uptake, phosphorus release to nitrate removaland phosphorus uptake to phosphorus release by denitrifying phosphate accumulating organisms in the system composed of an anaerobic reactor and an anoxic reactor as the change of the influent nitrate loading. The influent concentrations of COD, NH4+−N and PO4−P were 300, 20 and 6 mg/L, respectively, whereas the influent nitrate concentrations were varied at 10, 15, 20 and 30 mg/L. As aresult, the ratio of phosphorus release to carbon uptake was increased in accordance with nitrate supply. The denitrifying phosphate accumulating organisms simultaneously took up phosphate and removed nitrate from the anoxic reactor. With above 20 mg/L of sufficient NO3−−N supply, phosphate was taken up excessively by the DNPAOs in anoxic condition, resulting in the ratio of phosphorus uptake to nitrate removal to be 1.97. The large amount of both uptake and release of phosphorus occurred above 20 mg/L of nitrate supply, achieving the ratio of phosphorus uptake to phosphorus release to be 1.05. Conversely, if nitrate as the electron acceptor was limited, the ratio was found to be low.