MITIGATION OF ADVERSE EFFECTS OF ZINC OXIDE NANOPARTICLES ON ENHANCED BIOLOGICAL PHOSPHORUS REMOVAL: ROLE OF CARBON SOURCE CONCENTRATION

The potential risks of zinc oxide nanoparticles (ZnO NPs) to wastewater treatment processes have received much attention due to their large-scale production and application. However, little information is available regarding the mitigation of nanomaterials-induced negative effects on biological nutrient removal. In this study, an effective method, i.e., by increasing carbon source concentration, for mitigating ZnO NPs-induced toxicity to the performance of enhanced biological phosphorus removal (EBPR) was reported. When the microorganisms of a lab-scale EBPR were exposed to ZnO NPs of 5 mg/L, the effluent soluble ortho-phosphorus (SOP) concentration could be remarkably decreased from 13.2 to 0.7 mg/L by the increase of influent carbon concentration from 100 to 300 mg chemical oxygen demand (COD)/L. The mechanism investigation showed that the increase in carbon source concentration enhanced the viability of activated sludge and the metabolism of phosphorus-accumulating organisms. Further enzyme assays revealed that the activities of key enzymes (exopolyphosphatase and polyphosphate kinase) related to phosphorus removal were improved by the increase in carbon source concentration.