Assessing the effect of SiO2 and TiO2 nanoparticles on granule stability and microbial community shift in aerobic granular sludge process

The widely used SiO 2 and TiO 2 nanoparticles (NPs) can accumulate in industrial wastewaters , thereby posing challenge to biological wastewater treatment processes. In this work, the performance of aerobic granular sludge (AGS) reactors fed with wastewater containing 50 mg L −1 SiO 2 and TiO 2 NPs were investigated. The results showed that the granules could resist the NPs in wastewater (no disintegration of granules was observed). SiO 2 NPs had a negative effect on the settleability of granules, with the SVI 30 increased by 64.5% and protein secretion decreased by 29.9%. To the contrary, the settleability of granules was improved in the presence of TiO 2 NPs due to the increase of the protein secretion. Possibly because of the compact and layered structure of granules, in the presence of both types of NPs, no obvious reduction of the overall removal efficiency of organics was found, and nanoparticle-resistant strains were enriched. The overall nitrification and denitrification efficiencies were hardly affected by SiO 2 NPs while significantly inhibited by TiO 2 NPs. Some functional genera, such as Hyphomicrobium and Acidovorax , showed growth inhibition with TiO 2 NPs, which might be responsible for the reduction of nitrification and denitrification efficiencies.