The tolerance of a thin-film composite polyamide reverse osmosis membrane to hydrogen peroxide exposure

Abstract

Understanding the tolerance of thin-film composite (TFC) polyamide (PA) membranes to hydrogen peroxide (H2O2) is prerequisite to evaluate its use as biofouling control agent in reverse osmosis (RO) systems. H2O2 is potentially an alternative to the commonly applied chlorine-based disinfectants hypochlorous acid (HOCl) and monochloramine (MCA) that degrade PA membranes and form disinfection byproducts. The tolerance of the PA separation layer of a commercial RO membrane (ESPA2, Nitto Denko Hydranautics, Oceanside, USA) to H2O2 exposure was evaluated using a recirculating flat-sheet RO test system under corrosion-suppressed conditions. Membrane samples were exposed to 2.0mM (68mg/L), 10mM (340mg/L), 25mM (850mg/L) and 50mM (1,700mg/L) H2O2 for up to 24 days at 25°C in phosphate buffer at pH 7.2 without and with methanol present. Membrane performance was evaluated by measuring water flux and rejection of phosphate buffer and acesulfame (ACE), a common organic wastewater indicator compound. Membrane breakdown was assessed by water flux increase and loss of solute rejection. Without methanol, the membrane was stable in 1,700mg/L for at least 18 d, corresponding to a maximum tolerated dose (Dmax) of >744,000ppm-h. At initial concentrations of 20mM methanol and exposure to 850mg/L and 1,700mg/L H2O2, membrane breakdown occurred after approximately 18 days and 10 days, corresponding to Dmax of 367,200ppm-h and 408,000ppm-h, respectively. The time to membrane breakdown was defined as decrease of salt rejection of at least 0.5% within 24h. Membrane characterization employing X-ray photoelectron spectroscopy (XPS), Fourier Transform Infrared Spectroscopy (FTIR) and Scanning Electron Microscopy with Energy Disperse X-ray spectroscopy (SEM-EDS) failed to reveal membrane oxidation.