Removal of Emerging Wastewater Organic Contaminants by Polyelectrolyte Multilayer Nanofiltration Membranes with Tailored Selectivity

Emerging organic contaminants (EOCs) discharged from wastewater effluents into drinking water resources are of growing concern for human health and the environment. In this study, we demonstrate the fabrication and application of polyelectrolyte multilayer (PEM) nanofiltration (NF) membranes with tailored selectivity for effective removal of EOCs from saline wastewaters. The PEM NF membranes were prepared via layer-by-layer (LbL) assembly of a cationic polymer, i.e., poly(diallyl dimethylammonium chloride), and anionic polymer, i.e., poly(sodium styrenesulfonate). Extensive surface characterization verifies that the fabricated PEM membranes have different pore sizes and surface charge properties depending on the LbL deposition cycle. We evaluated the performance of the PEM NF membranes for the rejection of different salts as well as the retention of representative EOCs, including perfluoroalkyl substances (perfluorooctanoic acid and perfluorooctanesulfonic acid) and antibiotics (amoxicillin trihydrate and tetracycline hydrochloride). Importantly, the PEM NF membrane coated with four bilayers showed as high as 90% EOC retention, comparable to the widely used commercial NF270 membrane, while allowing high passage of salt, including scale-forming divalent cations (<20% rejections of NaCl and CaCl₂). This tailored selectivity of the four-bilayer PEM membrane enables high water flux and reduced inorganic (gypsum) scaling potential compared to the NF270 membrane during treatment of EOC-contaminated wastewaters.