Testing of water treatment copolymers for compatibility with polyamide reverse osmosis membranes

Abstract

Abstract Cationic polymers used in traditional water and wastewater treatment, in theory, will bind to the partially negatively charged polyamide membrane during reverse osmosis (RO) treatment. This study tested a variety of cationic, anionic, and nonionic polymers in terms of (1) aiding in turbidity removal when used in conjunction with alum coagulation [10 mg/L as Al 2 (SO 4 ) 3 ·14H 2 O], sedimentation, and dual‐media filtration; and (2) their binding affinity toward a polyamide membrane. Binding affinity was tested by exposing polyamide RO membranes to 50 mg/L of each polymer for 48 h and then conducting attenuated total reflectance Fourier transform infrared (FTIR) spectroscopy on the membrane samples and principal‐component analysis (PCA) of the FTIR spectra. Results from the turbidity removal tests showed that cationic polymers provided the lowest median effluent turbidity (0.03–0.11 NTU), followed by anionic polymers (0.06–0.08 NTU), and finally nonionic polymers (0.11–0.17 NTU). Although PCA of the FTIR spectra did detect differences in polymer‐exposed membranes vs. a control, no discernable difference in RO membrane performance was observed. Therefore, under the conditions studied, the issue of “membrane poisoning ” caused by organic polymer absorption onto polyamide membranes was minimal. © 2005 American Institute of Chemical Engineers Environ Prog, 2005