Long-term impacts of titanium dioxide nanoparticles (TiO2 NPs) on performance and microbial community of activated sludge

•SAOR and SNOR reduced with an increase in TiO2 NPs concentration from 0 to 60mg/L.•SPUR and SPRR decreased at 0–5mg/L TiO2 NPs and increased at 10–60mg/L TiO2 NPs.•TiO2 NPs affected the microbial enzymatic activity of activated sludge.•High TiO2 NPs concentration could promote the ROS production and LDH release.•TiO2 NPs exerted obvious impacts on the microbial richness and diversity of SBR. The long-term impacts of titanium dioxide nanoparticles (TiO2 NPs) on the performance and microbial community of activated sludge were evaluated in a sequencing batch reactor (SBR). TiO2 NPs impacted the COD and phosphorus removals of activated sludge, whereas the NH4+-N removal efficiency had no distinct change at 0–60mg/L TiO2 NPs. The presence of TiO2 NPs obviously inhibited the organic matter and nitrogen removal rates of activated sludge. The phosphorus removal rate gradually reduced at 0–5mg/L TiO2 NPs and then increased at 10–60mg/L TiO2 NPs. The removal rates of organic matter, nitrogen and phosphorus had the similar varying trends to the corresponding microbial enzymatic activities. High TiO2 NPs concentration promoted more reactive oxygen species (ROS) production and lactate dehydrogenase (LDH) release of activated sludge. The microbial richness and diversity of activated sludge were obviously affected at the phyla, class and genus levels.