Effects of CeO2 nanoparticles on bacterial community and molecular ecological network in activated sludge system

Highlights: • CeO₂ NPs induced serious deterioration of denitrification. • CeO₂ NPs inhibited the activities of NAR and NIR. • CeO₂ NPs altered the overall structure of bacterial communities. • CeO₂ NPs decreased the denitrifying genera of Flexibacter and Acinetobacter. • CeO₂ NPs promoted the completion in the network of microbial communities. The increasing use of cerium oxide nanoparticles (CeO₂ NPs) has caused concerns regarding their potential environmental risks. However, their effects on bacterial communities and network interactions in activated sludge process are still unclear. In this study, we carried out long-term exposure experiments (210 d) to investigate the influence of CeO₂ NPs on wastewater treatment performance, bacterial community structure and network interactions in activated sludge systems. The results showed that long-term exposure to 1 mg/L CeO₂ NPs induced the deterioration of denitrifying process, which was consistent with the inhibition of enzyme activities of nitrite oxidoreductase and nitrate reductase under CeO₂ NPs. CeO₂ NPs decreased the bacterial diversity and altered the overall bacterial community structure in activated sludge. Some dominant denitrifying bacteria, such as Flexibacter and Acinetobacter decreased significantly. Molecular ecological network analysis showed that CeO₂ NPs decreased the network complexity of bacterial community, and probably promoted the competition in bacterial communities of activated sludge. These changes of denitrifying bacteria and the bacterial network may be relevant to the deterioration of denitrifying process. This study provides insights into how the bacteria community and their molecular ecological network respond to CeO₂ NPs in activated sludge systems.