Effect of Functional Chemistry on the Rejection of Low-Molecular Weight Neutral Organics through Reverse Osmosis Membranes for Potable Reuse

Potable reuse facilities must be designed and operated to minimize the presence of contaminants of emerging concern (CECs) and other trace organics in the product water. Reverse osmosis (RO) is incorporated into the process train of many potable reuse facilities and has been demonstrated to achieve excellent removal of many, but not all, organic compounds. Organics that may be poorly removed by RO include low-molecular weight (MW) neutral compounds. This laboratory study examined the rejection of 73 low-MW neutral organics through a commercial RO membrane that is commonly used in potable reuse applications. The organics were selected using a reductionist approach so that the effect of individual functional groups on rejection could be ascertained. The research demonstrated that halogens, carbonyl functional groups, C═C double bonds, and aromaticity decrease rejection, that methyl and hydroxyl functional groups increase rejection, and that the position of functional groups in structural isomers has a significant effect on rejection. The results help explain the discrepancies and inconsistencies in RO rejection of neutral organics that are observed when considered from the conventional perspective of molecular size and hydrophobicity.