Targeted Regulation of Partial Nitrification/Anammox via Hydroxylamine Dosing: Performance, Measures, Microbial Community Changes, and Inhibition Mechanisms

Stringent effluent nitrogen limits often force over-aeration at the tail end of single-stage partial nitrification/anammox (PN/A) reactors, inadvertently reactivating nitrite oxidizing bacteria (NOB) and destabilising partial nitritation. This study explores the regulatory measures for PN and changes in microbial community structure in PN/A systems under excessive aeration conditions. The research results indicate that 5.00 mg/L hydroxylamine (NH2OH) successfully maintained PN in over-aeration PN/A, achieving NH4+-N and TN removal efficiencies of 99.94% and 96.02%, respectively. NH2OH selectively inhibited Nitrobacter, concomitantly increasing overall community diversity and total microbial abundance. Intermittent NH2OH addition upregulated the expression of amo and hao genes by 1.59 and 1.56 times, while reducing the expression of nxr gene by 23.70%. In addition, the abundance of Nicotinamide Adenine Dinucleotide Hydride (NADH) related genes decreased (0.56% to 0.47%) while Adenosine Triphosphate (ATP) synthesis related genes increased (0.20% to 0.22%), optimizing energy metabolism efficiency. Concurrently, the abundance of quorum sensing (QS) related genera Nitrosomonas and Nitrospira increased from 1.86% and 1.64% to 2.93% and 1.92%, respectively. These findings elucidate the inhibition mechanism of NH2OH and provide practical guidance for implementing robust PN/A in mainstream wastewater treatment.