Metal oxide nanoparticles resonate to ammonium removal through influencing Mg absorption by Pseudomonas putida Y-9.

Most metal oxide nanoparticles (NPs) can impact ammonium removal, but the underlying mechanism remains unclear. In this study, high doses of NiO, CuO, ZnO and TiO (>1 mg/L) inhibited the ammonium removal performance of Pseudomonas putida Y-9. Interestingly, low levels of CuO NPs (0.1, 0.5 mg/L) and NiO NPs (0.1 mg/L) enhanced ammonium removal efficiency. Moreover, a decrease in Mg levels was significantly positively correlated with ammonium removal efficiency, while negatively correlated with the Ti, Zn, and Cu release of NPs. Further research on effect of NPs and their corresponding cations on ammonium removal revealed that four NPs affected Mg absorption in Y-9 via different routes, thus impacting NH removal efficiency, i.e., the effect of NiO NPs was caused by itself, TiO NPs' impact was solely due to the release Ti, while the influence of CuO NPs and ZnO NPs was based on both the particles and released ions.