Performance evaluation and microbial community shift of a sequencing batch reactor under silica nanoparticles stress

•SiO2 NPs inhibited nitrifying rate and nitrite reduction rate of activated sludge.•SPUR and SPRR decreased with the increase of SiO2 NPs from 0 to 30 mg/L.•Nitrogen and phosphorus removal rates were related to microbial enzymatic activity.•SiO2 NPs promoted the ROS production and LDH release of activated sludge.•SiO2 NPs affected the microbial richness and diversity of activated sludge.

The performance, microbial community and enzymatic activity of a sequencing batch reactor (SBR) were evaluated at different silica nanoparticles (SiO2 NPs) concentrations. SiO2 NPs concentration at 5-30 mg/L had a slight inhibitory impact on the nitrogen and COD removals, whereas the phosphorus removal was obviously inhibited at 30 mg/L SiO2 NPs. The rates of nitrification, nitrite reduction and phosphorus removal decreased with the increase of SiO2 NPs concentration. The nitrate reduction rate decreased at less than 5 mg/L SiO2 NPs and subsequently showed an increase at 10-30 mg/L SiO2 NPs. The organic matter, nitrogen and phosphorus removal rates had similar varying tendencies to the corresponding microbial enzymatic activities under SiO2 NPs stress. Some SiO2 NPs were firstly absorbed on sludge surface and subsequently entered the interior of the microbial cells, which could exert the biological toxicity to activated sludge. The microbial community showed some obvious variations under SiO2 NPs stress.