A nanofiltration and electrocatalytic membrane reactor with ozone oxidation integrated system for dyeing wastewater treatment and Na2SO4 recovery

Removal of organic pollutants while recovering Na2SO4 is crucial for the dyeing wastewater resourcefulness. In this study, nanofiltration (NF) was used for the treatment of industrial dyeing wastewater (COD=294.2 mg L- 1, the concentration of Na2SO4 = 3.8 g L- 1). An electrochemical membrane reactor (ECMR) was then constructed with conductive carbon membrane (CM) as cathode and graphite as anode for the organic removal from the NF concentrate with high concentration of Na2SO4 for reuse. Meanwhile, ECMR was also coupled with ozone (O3) to enhance its performance. Electron spin resonance (ESR) was employed to investigate the generation of active species during the ECMR-O3 system. The organics were analyzed by excitation-emission matrix (EEM). The results show that Na2SO4 concentration of 18.4 g L- 1and purity of 92.4 % were achieved from the NF concentrate. After the NF concentrate was treated by ECMR-O3 system, the COD reduced to 48.6 mg L- 1 with a removal rate of 92.7 %, which was higher than that of O3 oxidation (57.7 %) and ECMR (13.9 %) alone. It was ascribed to the electrolysis of O3 flowed through the cathodic CM, leading to more HO center dot produced. Certainly, the high concentration of Na2SO4 in the NF concentrate provided a high conductivity environment for the optimal operating of ECMR and the CM promoted the enhanced mass transfer under the diffusive conditions of O3. The NF concentrate treated could be directly reused for dyeing fabrics, making a profit of 0.25 $ m- 3 and reducing a carbon emission of 46.81 %. (2.79 kg CO2 m- 3). In a word, this study offers a viable approach for dyeing wastewater treatment and Na2SO4 resources recover.