Formation of microbial products by activated sludge in the presence of sulfamethoxazole (SMZ) and zinc oxide nanoparticles (ZnO NPs) in long-term operated sequencing batch reactors

Emerging contaminants, sulfamethoxazole (SMZ) and zinc oxide nanoparticles (ZnO NPs), were selected as the target pollutants for this study and using a sequencing batch reactor (SBR), the coexistence effect of antibiotics and nanomaterials on the activated sludge system was investigated. The results showed that the average total nitrogen (TN) removal rates during long-term operation (60 days) for the blank group, the reactor with SMZ, ZnO NPs, and SMZ combined with ZnO NPs were 80.47 %, 78.22 %, 73.77 %, and 72.52 %, respectively, and the average total phosphorous (TP) removal rates were 84.17 %, 82.48 %, 74.69 %, and 76.20 %, respectively. This indicates that ZnO NPs, rather than SMZ, have a negative effect on the treatment efficiency of the system, whereas the coexistence of the two has not yet had a higher effect. Both SMZ and ZnO NPs caused an increase in soluble microbial products (SMP) and extracellular polymers (EPS). High-throughput sequencing results showed that the relative abundance of nitrifying, denitrifying, and phosphorus-polymerizing bacteria was the highest in reactor R1, and the long-term stress of either SMZ or ZnO NPs caused a decrease in these functional bacteria. Finally, the comprehensive mechanism of SMZ and ZnO NPs in activated sludge is discussed.