Inhibition of Nitrospira and Nitrotoga by paracetamol achieved the rapid start-up and long-term stable operation of partial nitrification for low-strength ammonium wastewater

Achieving stable partial nitrification (PN) are the basic guarantee of anaerobic ammonia oxidation (anammox) process. However, there is no recognized feasible method for rapidly achieving stable PN in municipal wastewater, and further research is necessary. In this study, paracetamol was proved as an effective nitrite oxidation inhibitor through long-term experiment lasting 392 days in three systems (floc sludge, granular sludge, biofilm). PN of low-strength ammonium wastewater was rapidly achieved within 28 days and maintained for about 80 days after paracetamol dose, whereas PN recovered again within 10 days and sustained over 150 days under paracetamol dose combined with low dissolved oxygen strategy. The inhibition effect of paracetamol on NOB was almost not affected by biomass growth modes. QPCR and high-throughput sequencing showed that Nitrospira (Oligotype 1) was inhibited by paracetamol, and PICURSt2 analysis indicated its key enzyme NXR was significantly downregulated after paracetamol treatment, which were the key reasons of PN start-up in three systems. The emergence and adaptation of Nitrotoga was the main reason for the instability of PN. This study proved that paracetamol could be used as a novel nitrite oxidation inhibitor, and provided a possibility to achieve the mainstream PN and anammox for treating wastewater with low-strength ammonium.