Inhibition Kinetics of Ammonia Oxidation Influenced by Silver Nanoparticles

Abstract

Silver nanoparticles (AgNPs) have significantly increased in production and use for anti-microbial propose. This agent, after used, is released into sewerage system resulting in possibility to inactivate non-targeted microorganisms in wastewater treatment plants. In this study, the inhibitory effect of AgNPs on ammonia oxidation was investigated using respirometric assay. The initial concentrations of AgNPs and ammonia ranged 0.25–10.00 and 14–280 mg/L, respectively. Half saturation constant (Ks) for ammonia oxidation was found to be 15.9 mg N/L. Under the presence of AgNPs, the maximum oxygen uptake rate and Ks declined. The effect of AgNPs was proved to follow an uncompetitive-like inhibition kinetic type with the inhibition coefficients (Ki) of 5.5 mg/L. Increasing AgNPs from 0.25 to 10.00 mg/L inhibited 4 to 50 % of ammonia-oxidizing activities at the initial ammonia concentrations from 14 to 280 mg/L. Based on transmission electron microscopic observation, AgNPs could damage the microbial cells. All findings indicated that AgNPs substantially reduced ammonia-oxidizing microorganisms and their activities. Thus, special attention should be made to manage discharge of AgNPs into the environment.