Enhancement of solute removal efficiency of polyamide reverse osmosis membrane without water permeability loss

This study investigates the enhancement of the solute removal efficiency of reverse osmosis (RO) membranes without water permeability loss during the treatment of secondary wastewater effluent (SWE). First, filtration experiments were performed using a synthetic SWE containing three types of solutes with different membrane transport properties, namely arsenious acid (H3AsO3), electrolyte, and rhodamine-WT (R-WT), and alginate as a representative biopolymer foulant. The flux of R-WT at 2.0 MPa decreased by up to 45% in the presence of alginate without decreasing water permeability; this trend was not observed for H3AsO3 and the electrolyte, indicating that nanoscale imperfections that allow unselective solute transport were plugged by alginate. Second, H3AsO3 and R-WT were spiked into a real SWE that was pretreated using 0.1 mu m microfiltration, and the enhancement of solute removal efficiency was investigated. Membrane performance after 14 days of operation revealed that the flux of R-WT at 2.0 MPa decreased by up to 44% in the presence of the biopolymer. These results demonstrated that nanoscale imperfections in the RO membrane were plugged by the biopolymer contained in SWE and that the removal of large solutes was enhanced without forfeiting water permeability.