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

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.