Fate and behaviour of ZnO engineered nanoparticles in a simulated domestic wastewater treatment plant

Abstract

Wastewater treatment plants (WWTPs) employ activated sludge processes to treat domestic wastewater using a consortium of bacteria essentially to degrade organic matter. However, bacteria activity is inhibited by toxic substances; thus, potentially adversely impacting on the wastewater biological treatment processes. Among the increasing emerging contaminants into wastewater are engineered nanoparticles (ENPs). However, the impacts of these contaminants including metal oxides ENPs on the treatment efficiency of WWTPs are largely non-quantified. In addition, the fate and behaviour of ENPs from influent point to the effluent discharge point is not well established. Therefore, here findings on the fate and behaviour of ZnO ENPs derived using simulated (model) wastewater treatment plant developed following prescribed Organization for Economic Co-operation and Development (OECD) specifications are described. Preliminary results from our study using ICP-OES – for the analysis of zinc – suggest the release of low levels of zinc (about 50–200 ppb) in the effluent compared to concentrations in the sludge (about 2000 ppb). Our findings indicate efficiency removal of ZnO ENPs from domestic wastewater exceeding 90%. The findings suggest ZnO ENPs were removed from influent through abiotic, biosorption, and biosolid settling mechanisms. This phenomenon was confirmed using X-ray fluorescence spectroscopy (XRF) analysis showing the presence of zinc on the surface of the sludge. Overall, our results indicate that, after release of ENPs, for example ZnO, into WWTPs only low levels are likely to be released into the environment, but the sludge may require additional treatment steps due to elevated metallic concentrations.