A novel high-flux, thin-film composite reverse osmosis membrane modified by chitosan for advanced water treatment

Abstract

Membrane-based desalination is a proven and established technology for mitigating increasing water demand. The high-flux membrane will require lower pressure to produce the given quantity of water and therefore will consume less energy. This work demonstrates a novel method to produce a high-flux membrane by surface modification of thin-film composite reverse osmosis (TFC RO) membrane. TFC RO membrane was exposed to a sodium hypochlorite solution of 1250 mg l⁻¹ for 30 minutes and 60 minutes at pH 11.0, followed by 1000 mg l⁻¹ chitosan for 60 minutes at pH 2.5, and the solute rejection/flux were monitored. It was observed that there is up to 2.5 times increment in flux with ca. 3% increase in solute rejection in the case of chitosan-treated membrane. Although the flux increase is more in membrane with longer exposure to sodium hypochlorite, the decline in solute rejection was also significant. The membrane samples were characterized by attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) to understand the chemical structural changes in the membrane, atomic force microscopy to understand the morphological changes on membrane surface, zeta potential for surface charge and contact angle analysis to understand the change in hydrophilicity. The % rise in trans-membrane flux per °C rise in feed water temperature was more in the case of chitosan-modified membrane as compared to virgin TFC RO membrane. The higher temperature sensitivity makes it a good candidate for solar powered reverse osmosis, where low grade thermal energy can be utilized to increase feed water temperature, and higher temperature feed water gives more a pronounced advantage in trans-membrane flux.