Transformation and metabolism impact of ZnO-NPs on microalgal-bacterial granular sludge

Although the hazards of zinc oxide particles (ZnO-NPs) in the field of wastewater treatment are receiving more and more attention, the responses of metabolism and migration pathways of microalgal-bacterial symbiosis to ZnO-NPs have not been well understood. Here, the distribution of ZnO-NPs along with its impact on metabolism in microalgal-bacterial granular sludge (MBGS) was studied. The results showed that over 95% of ZnO-NPs in the MBGS system were absorbed by sludge or enriched in the sludge layer in the form of zinc oxide, while releasing a small amount of Zn2+. The adsorption of ZnO-NPs by MBGS mainly relied on the –OH functional groups and protein structures. After ZnO-NPs adsorption, the cell membrane could be destroyed, resulting in the release of lactate dehydrogenase. At the genetic level, ZnO-NPs promoted gene abundance levels related to biological processes and enzyme glycosyl transferase synthesis, but inhibited intracellular biosynthesis and metabolism of genetic material, especially glutathione synthesis. Key functional and biosynthetic genes involved in metabolic processes were also inhibited, such as acs and glnA. This study explained in detail how ZnO-NPs altered and impacted on MBGS, which provided a reference for future practical applications of MBGS for wastewater treatment containing nanoparticles.