Influence of ZnO nanoparticles on anammox granules: The inhibition kinetics and mechanism analysis by batch assays

The spread application of nanoparticles (NPs) would cause instability on anaerobic ammonium oxidation (anammox) process. The present study focused on the short-term evaluation of ZnO nanoparticles (NPs) on anammox process by batch tests. Results indicated that a significant inhibition occurred under ZnO NPs stress of 5-100 mg gVSS−1. The half inhibitory concentration (IC50) of ZnO NPs was found to be 11.6 mg gVSS−1. The release of zinc ions from ZnO NPs dissolution was confirmed to be the main mechanism of inhibition on anammox activity. Haldane kinetic model simulation results confirmed that ZnO NPs imposed a non-competitive inhibition on nitrite conversion by decreasing maximum nitrogen removal rate (qmax), while they showed a competitive inhibition on ammonium conversion kinetics with affinity constant (Ks) increasing by 6 times. From the competitive inhibition results, it is suggested that the inhibition caused by ZnO NPs could be alleviated and recovered under higher ammonium concentrations.