Elucidation of the stress mechanisms on activated sludge stability induced by yttrium oxide nanoparticles with cytotoxicity: Performance deterioration, biointerface variation and microbial response.

As technoscience advances, widespread use of nanoparticles (NPs) has resulted in environmental risks. This study focuses on the potential stress of 0-200 mg/L yttrium oxide (YO) NPs on the activated sludge stability. YO NPs progressively suppressed nitrification, caused significant NO accumulation (200 mg/L) and diminished activities of key functional enzymes. Deteriorated flocculation corroborates the YO NPs' destruction. Extracellular polymeric substances were lessened, yet amplified microbial metabolites prove the microbial counteraction coping with YO NPs' cytotoxicity. Plausible blockage of different protein channels contributed to the wane in biological nitrogen-removal capacity. Plus, 50 mg/L YO NPs stimulated the β-glucan production. When exceeding 100 mg/L, plentiful YO NPs aggregate on sludge-surface, which inhibits nutrients transfer and metabolism. Furthermore, ammonia-oxidizing bacteria shifted from Nitrosomonas to Nitrosospira with YO NPs increase. Reduction in Nitrospira, Saccharimonada-genera, and Microlunatus further corroborates the impairment of pollutants removal. PICRUSt2 prediction demonstrates YO NPs impedes nitrogen and glycolytic metabolic pathway.