Effects of feedwater pretreatment on the removal of organic microconstituents by a low fouling reverse osmosis membrane

The removal of 16 organic microconstituents by a commercially available low-fouling RO membrane was systematically investigated in this study under different feedwater pretreatment conditions, including magnetic ion exchange (MIEX), alum coagulation and ultrafiltration (UF). It was found that organic microconstituents were consistently removed by RO despite noticeable changes in the composition of feedwater natural organic matter (NOM) as determined by size exclusion chromatography. Sequential treatment of the natural water by MIEX, coagulation, UF, and RO revealed that MIEX removed more than 70% of NOM, but less than 40% of the microconstituents while RO was capable of removing more than 90% of the target organics, regardless of their chemical properties. These findings suggest that RO treatment is effective in removing organic microconstituents in natural water that have molecular weights greater than the molecular weight cutoff of the membrane, while MIEX, coagulation, and UF are not effective means for enhancing organic microconstituent removal by RO. Meanwhile, the fouling of the RO membrane by an ultra-filtered natural surface water was minor and not influenced by the variations in organic composition after different pretreatment schemes, indicating the potential of combining membrane modification and UF pretreatment for effective control of RO membrane fouling. ►Impact of magnetic ion exchange (MIEX) on the removal of organic microconstituent by reverse osmosis (RO) was investigated. ►MIEX pretreatment was more effective than coagulation or ultrafiltration in removing organic microconstituents. ►Membrane modification and ultrafiltration effectively controlled membrane fouling, resulting in consistent organic removal. ►RO was the major treatment for organic removal, regardless of pretreatment schemes.