Arsenic(V) removal from water using polyelectrolyte enhanced ultrafiltration with poly(dimethyldiallylammonium chloride) (PDADMAC): Ion-selectivity based modeling and electric field influence

Polyelectrolyte enhanced ultrafiltration (PEUF) shows promise for arsenic removal. However, competing ions may serve as potential limiting factors, and membrane fouling caused by aggregation of polyelectrolytes may impact PEUF performance. This study employed poly(dimethyldiallylammonium chloride) (PDADMAC) for arsenate (As(V)) removal via ultrafiltration, and the effect of electric field assistance on PEUF performance was investigated. Ion exchange experiments between Cl- and typical anions were conducted in a binary system to determine the selectivity coefficients (K-sel) of PDADMAC for different anions. The affinity of PDADMAC towards common monovalent anions was found to be Br->NO3->Cl->H2PO4->HCO3->H2AsO4-, while its affinity for divalent anions decreased in the order SO42-> HPO42-> HAsO42-. By determining the selectivity coefficients of various anions with PDADMAC and utilizing mass conservation models, a phase distribution model for anions during PEUF process was developed to predict As(V) removal. Predictions were made regarding the enhanced ultrafiltration efficiency for As(V) under different conditions (pH, ionic strength, and competing anions) in complex water environments. As the dosage of PDADMAC increased, the removal of As(V) from the actual water sample spiked with an initial concentration of 0.2 mM exceeded 90 %, and the experimental results closely matched the model predictions. The impact of electric field on the PEUF process was investigated by placing electrodes on both sides of the ultrafiltration membrane. Results showed that the ultrafiltration membrane, when positively charged by an electric field, repelled cationic PDADMAC, thereby alleviating membrane fouling. However, the cleaner membrane led to increased leakage of PDADMAC molecules, resulting in the co-loss of As with PDADMAC and consequently reducing the overall As removal.