Hydroxylamine-based cometabolism of ammonium-oxidizing bacteria: chloroquine biodegradation and associated nitrogen conversions

Despite the well-reported ability of ammonium-oxidizing bacteria (AOB) to cometabolize non-growth substrates, most relevant studies were substantiated with the ammonium oxidation activity as the driving force and didn't further explore/verify/distinguish the contribution of the hydroxylamine oxidation process of AOB. Therefore, using highly enriched AOB-dominated sludge, a series of dedicated batch tests were conducted in this work to investigate the hydroxylamine-based cometabolic degradation of chloroquine (CLQ), a widely applied drug with a significant environmental concern, and its associated impacts on the nitrogen conversions of AOB. The results indicated that the hydroxylamine oxidation process of AOB could trigger the degradation of CLQ which achieved 0.4-1.2 mg/L CLQ removal under the studied conditions, despite the potentially preferred utilization of CLQ degradation products towards mineralization by AOB over CLQ itself. CLQ and its degradation products wouldn't affect the hydroxylamine oxidation process or the associated N2O production through the hydroxylamine oxidation pathway of AOB. We hope this work will not only provide new perspectives for prospective research on the cometabolic capacity and features of AOB but also inspire the revisit of the literature-reported research on such an important topic.