The impact of zinc oxide nanoparticles on phosphorus removal and the microbial community in activated sludge in an SBR

Abstract

The impact of zinc oxide nanoparticles (ZnO NPs) on phosphorus removal and the microbial community was investigated after long-term exposure to a simulated SBR. ZnO NPs at low concentrations (1, 5 mg L⁻¹) did not exert an obvious impact on phosphorus removal, but the removal efficiency decreased by 20% and 75%, respectively, in the presence of 10 and 20 mg L⁻¹ ZnO NPs. At these concentrations, ZnO NPs inhibited the activity of exopolyphosphatase (PPX) and polyphosphate kinase (PPK), and extracellular polymeric substance (EPS) production and destroyed the integrity of cell membranes. High-throughput sequencing analysis revealed that 20 mg L⁻¹ ZnO NPs led to an obvious decrease in the community diversity and a shift in the community structure. In addition, the exposure to 10 and 20 mg L⁻¹ ZnO NPs resulted in a decrease in the proportion of Betaproteobacteria and Rhodocyclales (polyphosphate accumulation organisms, PAOs) in the community and led to a promotion in the growth of Alphaproteobacteria and Gammaproteobacteria (glycogen accumulating organisms, GAOs). These findings meaningfully show the adverse effects of NPs on activated sludge in wastewater treatment.