[Size-dependent Effects of Zinc Oxide Nanoparticles on Performance and Microbial Community Structure of a Constructed...

Nanoparticles (NPs) have increasingly been applied in consumer and industrial products because of their magnetic, optical, electronic, sensitive, antibacterial, disinfection, and UV shielding properties. The wide production and application of NPs has inevitably resulted in their release into the ecosystem through various channels and accumulation in organisms. NPs have a small particle size (1-100 nm), which is closely correlated with biotoxicity. To investigate the size-dependent effects of zinc oxide nanoparticles (ZnO NPs) on microbial community structure and diversity, as well as the nitrogen removal performance of a biological treatment system, laboratory scale horizontal subsurface flow constructed wetlands were operated for 28 days under the conditions of COD 200.0 mg·L^-1, NH₄⁺-N 12.5 mg·L^-1, and total dissolved phosphorus 4.0 mg·L^-1. The relationship between microbial community structure and its performance were discussed. The results indicated that three sized ZnO NPs (15, 50, and 90 nm) had no significant effect on COD removal at the concentration of 10 mg·L^-1 but showed obvious particle size effects on nitrogen removal. High throughput sequencing indicated that the abundance of nitrifying bacteria in constructed wetland system was significantly lower than that of denitrifying bacteria, suggesting that the nitrification process was the key factor restricting the denitrification performance of wetlands. After exposure to ZnO NPs, the structure of microbial communities in constructed wetlands changed, and 15 nm ZnO NPs had a stronger inhibitory effect on nitrifying bacteria than those of 50 nm and 90 nm ZnO NPs.