Critical review and comprehensive analysis of trace organic compound (TOrC) removal with polyamide RO/NF membranes: Mechanisms and materials

Trace organic compounds (TOrCs) have emerged as a critical concern for securing high-quality and safe water resources. Advanced water treatment using reverse osmosis (RO) and nanofiltration (NF) membranes has proven to be a promising technology for removing TOrCs. In this context, identifying the TOrC rejection mechanisms of RO/NF membranes is of paramount importance for the effective design of membrane processes and materials to improve the efficiency of TOrC treatment. However, the characteristic TOrC removal mechanisms of RO/NF membranes remain unclear, presumably due to the vast differences in the membrane structures and the limited number of TOrCs that have been investigated in past studies. Hence, the present article comprehensively reviews, analyzes and elucidates TOrC rejection mechanisms by characterizing key rejection-governing solute parameters for fully-aromatic polyamide-based tight RO/NF membranes (MWCO ≤ 200 Da) using the published rejection data for a large number of TOrCs (>300). We found that size exclusion and adsorption (and subsequent partitioning) via specific interactions play a dominant role in TOrC rejection by elucidating the key rejection-governing solute characteristics. In addition, this paper outlines up-to-date research on the fabrication of advanced membranes designed to improve TOrC removal performance. Based on this review, we propose future directions for reliably predicting and effectively enhancing the TOrC separation performance of RO/NF membranes.