Removal of pesticides by nanofiltration: effect of the water matrix

This study explores the removal of two pesticides (atrazine and simazine) from different water matrices (distilled water, tap water and river water) by nanofiltration (NF), using four types of nanofiltration membranes (DESAL 51 HL, DESAL 5 DL, UTC-20, UTC-60). Atrazine or simazine was added to the different water matrices at a concentration of 5 mg/l and 100 μg/l. Rejection of pesticides and the water flux were measured. The rejection of atrazine was always higher than the rejection of simazine; the highest rejections were obtained with UTC-20. The rejection of pesticides was higher in river water and tap water than in distilled water, but the water flux was lower. This was mainly explained by ion adsorption inside the membrane pores. Narrower pore size counteracted the effect of presence of natural organic matter (NOM). The NOM was assumed to enhance the adsorption of pesticides onto membranes surface, increased the size exclusion and electrostatic repulsion also appeared during the transport. Additionally, there was a small effect of NOM on rejection and flux. No significant effect of the pesticides concentration was observed. The rejections were the highest at pH 8 and decreased at higher and lower pH. Considerable rejections of nitrate and organic matter (measured as COD and UV absorbance at 254 nm) were observed, in particular for the membrane with the smallest pores (UTC-20). This confirms the assumption that pore narrowing by ion adsorption influences the rejections and water fluxes.