Recovery of Acid and Alkaline from Industrial Saline Wastewater by Bipolar Membrane Electrodialysis under High-Chemical Oxygen Demand Concentration

Abstract

Actual high saline wastewater containing concentrated organics and sodium chloride is a bioenergy and renewable resource. This study compared two different bipolar membrane electrodialysis membranes from two companies' stacks to recover HCl and NaOH from sodium chloride solution and actual chemical wastewater. The results demonstrated that the electrolysis rates were around 1.5 kg/m2h, the HCl and NaOH production rates were about 0.9 kg/m2h, energy consumption was in the range of 1.05-1.27 kWh/kg, and the economic benefits were above 1 yuan/h in BMED systems. From analyzing the performance of seven different BMED membrane stacks, the B2 stack was chosen for electrolyzing actual high salt wastewater to observe the effect of chemical oxygen demand on BMED systems, where electrolytic salt performance, HCl-NaOH alkali production rates, and energy consumption show linear dependence on time for 5000 mg/L chemical oxygen demand wastewater. It illustrated chemical oxygen demand can enhance energy consumption and reduce electrolytic salt performance and the acid and alkali production rates, due to improving the membrane area resistance. In this study, the effect of high COD saline wastewater on the performance of a BMED membrane stack was clarified and the mechanism was analyzed for its practical application in treating chemical high salt wastewater.