Nanocomposite cation-exchange membranes for wastewater electrodialysis: organic fouling, desalination performance, and toxicity testing

Abstract

Abstract Organic fouling hinders the application of membrane treatment of alternative water. In this study, polyethyleneimine (PEI), titanium dioxide (TiO2) nanoparticles, and graphene oxide (GO) nanosheets were used for modifying cation-exchange membranes to enhance anti-organic fouling and desalination performance during electrodialysis of synthetical water and municipal wastewater. Fouling propensity of the unmodified and modified membranes was quantitatively evaluated by measuring organic accumulation on membrane surface using humic acid (HA, simulating natural organic matter) and bovine serum albumin (BSA, simulating organic matter in municipal wastewater effluent) as model foulants. Significant surface deposition of HA was observed on the unmodified, PEI-TiO2, and PEI-modified membrane surfaces while trivial HA fouling was detected on the PEI-GO membrane. BSA fouling was minor for all the modified membranes compared to the unmodified membrane. Desalination efficiency of electrodialysis with the modified membranes, except the PEI-modified membrane, was significantly improved in treating synthetical water with HA foulant compared to the electrodialysis with the unmodified membrane (20%~40% reduction of normalized salt removal). Relatively stable desalination behaviors were observed for each membrane system in treating BSA-containing synthetical water, and enhanced desalination was demonstrated with the modified membranes. Subsequent long-term fouling experiments with wastewater effluent revealed the superior antifouling capacity of the nanocomposite membranes (especially for the PEI-GO membrane) over 100-hour operation, while the unmodified membranes exhibited severe fouling (with total more than 60% decline of normalized salt removal) after approximately 50-hour treating wastewater. In a standard Microtox® acute toxicity assay, the nanocomposite membranes did not show any acute toxicity towards Vibrio fischeri due to potential leaching of PEI and nanomaterials, indicating safe utilization of the modified membranes for water treatment.