Rejection behaviors of N-nitrosamines by initially fouled ultrafiltration and reverse osmosis membranes for municipal wastewater reclamation: A pilot study

Abstract

This study investigated the mechanisms underlying the removal of N-nitrosamines, an emerging class of trace organic contaminants, within a pilot system integrating combined coagulation and disk filtration (CC-DF), ultrafiltration (UF) and reverse osmosis (RO) membranes where membrane fouling occurred already during the long-term operation. Despite the limitations of CC-DF and UF processes in effectively rejecting N-nitrosamines, RO membranes are notable for their significant removal efficiencies (51.2 %-64.1 %). This study highlights the importance of N-nitrosamine hydrophilicity and its role in removal through complex water molecule mediated intermolecular hydrogen-bonding interactions with the fouling layers on membrane surfaces. The strong correlation between the N-nitrosamine hydrophilicity and removal efficiency emphasizes the critical importance of understanding the physicochemical properties of the fouling layers (% rejection: R2 = 0.96; solute permeability:R2 = 0.95). Hydrophilic N-nitrosamines are more likely to interact with water molecules, which results in the formation of intermolecular hydrogen bonds with the functional groups of humic-like substances (such as -COOH and -OH). By examining the rejection behaviors of N-nitrosamines within integrated UF and RO systems, this study enhances the understanding of the removal mechanisms not only for N-nitrosamines but also for neutral low-molecular-weight organic substances in the real RO process operations, providing crucial insights to bolster the sustainability of municipal wastewater reclamation.