Reverse osmosis concentrate (ROC) produced as the by-product of the reverse osmosis process consists of a high load of organics (macro and micro) that potentially cause eco-toxicological effects in the environment. Previous studies focused on the removal of such compounds using oxidation, adsorption, and membrane-based treatments. However, these methods were not always efficient and formed toxic by-products. The impact of ion-exchange resin (IEX) (Purolite®A502PS) was studied in a micro-filtration-IEX hybrid system to remove organics from ROC for varying doses of Purolite® A502PS (5-20 g/L) at a flux of 36 L/m2h. The purolite particles in the membrane reactor reduced membrane fouling, evidenced by the reduction of transmembrane pressure (TMP), by pre-adsorbing the organics, and by mechanically scouring the membrane. The dissolved organic carbon was reduced by 45-60%, out of which 48-81% of the hydrophilics were removed followed by the hydrophobics and low molecular weight compounds (LMWs). This was based on fluorescence excitation-emission matrix and liquid chromatography-organic carbon detection. Negatively charged and hydrophobic organic compounds were preferentially removed by resin. Long-term experiments with different daily replacements of resin are suggested to minimize the resin requirements and energy consumption.
Keywords: adsorption; dissolved organics; ion-exchange resin; micro-pollutants; reverse osmosis concentrate; submerged membrane system.