Response of poly-phosphate accumulating organisms to free nitrous acid inhibition under anoxic and aerobic conditions

► Free nitrous acid-adapted culture is more tolerant to FNA inhibition. ► Anoxic P-uptake is more sensitive to the inhibition compared to aerobic P-uptake. ► Electrons were channeled to nitrite reduction from oxygen reduction under inhibition. ► Anaerobic metabolism of PAO was observed at higher FNA concentrations. ► The anoxic and aerobic growth of PAOs decreased sharply with FNA concentration.