Release And Removal Mechanism Of Nanosilver Particles By Coagulantion Process

Great concerns have been raised about potential adverse effects of silver nanoparticles (AgNPs) on human health and the environment, as the widely use leads to AgNPs release into the environment. It’s necessary to find an effective way to remove nanosilver particles from water solution. In this study, AgNPs were synthesized by liquid phase reducing method and well characterized.The removal of AgNPs by the coagulation processes was investigated. Five common-used coagulations, including four inorganic coagulating agents:aluminum sulfate, polyaluminium chloride (PAC), ferric chloride, polyferric sulfate (PFS), and polymeric flocculant agent:polyacrylamide (PAM) were optimized based on the removal efficiency of AgNPs from a series of jar test experiments. Considering AgNPs would keep releasing dissolved silver in aquatic environment, both AgNPs and dissolved silver concentrations were analyzed to test the removal rate of AgNPs. These results should contribute to, in particular, further studies dealing with the nanoparticles level and risk in the coagulated effluents.AgNPs were synthesized from silver nitrate by adding sodium borohydride with polyvinyl alcohol (PVA) as a capping agent. Nanosliver particles were relatively pure, spherical in shape and well-dispersed with an average diameter of12nm.The concentrations of AgNPs in the wastewater solutions were determined by inductively coupled plasma mass spectrometry (ICP-MS) combined with ultrafiltration, The coagulation conditions, including the dosages of the coagulants and solution pH, were optimized based on the optimal dosages. Results showed that four inorganic coagulants, could provide sufficient AgNPs removal efficiency, with more than95%AgNPs removed, aluminum sulfate, ferric chloride, PAC and PFS, could be removed effectively with495mg/L,400mg/L,30mg/L,47mg/L dosage at pH7.5, and the best removal efficiency was97.3%,96.3%,95.9%,96.0%. However, another tested coagulant, PAM could not achieve the removal of AgNPs from wastewater, as zeta potential analysis showed the stability of AgNPs in the PAM solution.Transmission electron microscope (TEM) image and X-ray diffraction (XRD) spectra showed the formation of AgNPs in the coagulation floes, zeta analyser measured the zeta potential of nanosilver particles, in order to explain the removal mechanism of AgNPs. Meanwhile, the concentrations of dissolved silver ion in the solutions under different given conditions, the presence of coagulations was included, were determined by ICP-MS. The result suggested that one of the AgNPs removal mechanism could be the adsorption and settlement between AgNPs and floccs, the hydrolysis products of coagulation. Furthermore, the silver ion releasing from AgNPs and formed some indissoluble salts, such as AgCl, Ag2SO4, could be the other AgNPs removal mechanism. This study evidenced that coagulation process can assure the limits of nanosilver for municipal wastewater treatment plants if the process is well optimized and operated.Figure [17] table [18] reference [72]...