Effect of silver nanoparticles on an integrated fixed-film activated sludge-sequencing batch reactor: Performance and...

The effects of silver nanoparticles (AgNPs) on reactor performance, extracellular polymeric substances composition and microbial community structure and function in integrated fixed-film activated sludge-sequencing batch reactors (IFAS-SBRs) were investigated. Results showed that the addition of AgNPs from 0.1 to 10 mg/L exhibited no significant effects on nutrient removal. The average overall removal of COD, NH₄⁺-N and PO₄^3--P was 96.6%, 99.9% and 98.8%, respectively. The introduction of AgNPs caused an increase in extracellular polymeric substances content for the sludge and biofilm of IFAS-SBRs. The release of Ag⁺ from AgNPs and lactate dehydrogenase test implied the low toxicity of AgNPs to IFAS-SBRs. High-throughput sequencing revealed that microbial community structure showed significant shifts at phylum and genus levels after long-term exposure to AgNPs, but core functional groups responsible for nutrient removal remained at high abundance. Bacterial function prediction indicated that the metabolic categories showed no significant shifts under AgNPs stress, therefore good process performance could still be achieved.