Enhanced biological phosphate removal from wastewater and clade-level population dynamics of “Candidatus Accumulibacter phosphatis” under free nitrous acid inhibition: Linked with detoxication

“Candidatus Accumulibacter” are the dominant polyphosphate-accumulating organism (PAOs) to perform enhanced biological phosphate removal (EBPR) from wastewater. Free nitrous acid (FNA) as inhibitor is an intermediate of nitrification and denitrification commonly present in wastewater treatment plants (WWTPs) and lab-scale reactors. Impact of FNA on EBPR and community structures of Accumulibacter in domestic wastewater treatment was investigated. FNA complete inhibit concentration on aerobic P uptake at pH 6.5 was 6.85 × 10−3 mg HNO2-N/L, higher than that at pH 7.0. Under complete inhibition, poly-β-hydroxyalkanoates degradation was used for nitrite reduction and detoxication rather than P-uptake. The P fraction existed in the forms of complex-P, interstitial-P, chemical participated-P and ortho-P at the end of aerobic phase, and complex-P proportion declined in comparison to non-inhibition. Dominant Accumulibacter clade was IIC, accounting for 70% of total Accumulibacter. Decline of IIF proportion indicated its sensitivity to FNA. Increase of IID percentage implied its strong tolerance to FNA. Under inhibition, Shannon index decreased from 3.45 of seed sludge to 1.92 at pH 7.0, indicating decline of biodiversity. Therefore, FNA inhibition weakened EBPR performance, and remarkably changed clade-level community structures of Accumulibacter.