Exposure dose and temperature of chlorine on deterioration of thin-film composite membranes for reverse osmosis and nanofiltration

Abstract

In this study, the effect of chlorine, which is used as a chemical cleaning agent or disinfection agent on membrane deterioration, was analyzed under various conditions during the membrane process. Reverse osmosis (RO: ESPA2-LD and RE4040-BE) and nanofiltration (NF: NE4040-70) membranes made of polyamide (PA) thin film composite (TFC) were used for evaluation. Chlorine exposure was performed at doses ranging from 1000 ppm h to 10,000 ppm h using 10 ppm and 100 ppm, and temperatures from 10 °C to 30 °C. Raw water containing NaCl, MgSO₄, and dextrose was used to compare the filtration performance after exposure to each of the conditions studied. Reduction in removal performance and enhancement in permeability were observed as chlorine exposure increased. Attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy and scanning electron microscope (SEM) were employed to determine the surface characteristics of the decomposed membranes. ATR-FTIR was used to compare the intensity of the peaks related to the TFC membrane. Based on the analysis, the state of membrane degradation was elucidated. SEM was used to confirm visual degradation of the membrane surface. Permeability and correlation analyses were performed on CⁿT as an index for determining membrane lifetime in order to investigate the power coefficient. The relative influence of the exposure concentration and time on membrane degradation was explored by comparing the power efficiency according to the exposure dose and temperature.

Keywords: Chlorine; CnT parameter; Membrane lifetime; Power coefficient; Reverse osmosis.