Comparison of ALD coated nanofiltration membranes to unmodified commercial membranes in mine wastewater treatment

Abstract In this study, commercial nanofiltration (NF270 and NF90, Dow Filmtec) and zinc oxide (ZnO) coated NF270 nanofiltration membranes prepared by atomic layer deposition (ALD) were applied to the purification of mine wastewaters. The characteristics of the coated nanofiltration membranes were evaluated with contact angle, roughness and zeta-potential analyses. Membrane wearing was also studied from microscopic pictures. The waters used were purified process water and mildly contaminated wastewaters from mine sites. The target compounds were sulphate, manganese, nitrate and chloride, the removal efficiencies of which were studied. In addition, membrane fouling was under interest. It was observed that the flux recovery ratio (FRR) after the experiment was 73–85% and 83–93% with the original and the coated membranes, respectively. The relative flux was slightly increased with the coated membrane when testing the membrane efficiency with three different wastewaters. The ZnO layer on the active membrane surface reduced the reversible fouling of the NF270 membrane. Ion removal efficiencies of the coated membranes were in the same level with the uncoated membrane, i.e. removal efficiencies were high.