Mitigation of nitrification inhibition by silver nanoparticles using cell entrapment technique

Abstract

Effects of silver nanoparticles (AgNPs) on nitrification activities of free and entrapped nitrifying activated sludge (NAS) were investigated using a respirometric assay. Initial concentrations of ammonia and AgNPs, and entrapment materials and matrix sizes were the variables. Scanning and transmission electron microscopic analyses of the microbial cells and entrapment matrices were also performed. Results showed that AgNPs (0.05–5.00 mg/L) decreased nitrification activity down to only 2 % compared to the control (free NAS without AgNP exposure). Calcium alginate and polyvinyl alcohol-entrapped cells could mitigate inhibition of nitrification activity up to 100 % (no inhibition observed) and 88 % compared to the controls (entrapped NAS without AgNP exposure), respectively. Cells entrapped in a larger matrix size (both with and without AgNP exposure) performed nitrification better. Silver nanoparticles caused damages to cell membrane and cytoplasm, which likely led to a decrease of nitrification activity. The entrapment matrices successfully reduced the adverse effects of AgNPs on nitrification activity.