Treatment of Brackish Water RO Brine via Bipolar Membrane Electrodialysis
Chunliang Du, Jennifer Runhong Du, Xiangshan Zhao, Fang Cheng, Mohamed E.A. Ali, Xianshe Feng
Abstract
Due to the demand for acid and base in brackish water reverse osmosis (RO) desalination plants located in remote areas and the difficulty of transporting acid and base, bipolar membrane electrodialysis (BMED) was employed to convert brackish water RO brine into acid and base on site. The effects of operating parameters (i.e., initial salt content, current density, content of electrode solution, and initial HCl and NaOH contents) on the BMED performance for batch processing of brackish water RO brine were investigated with NaCl solutions. The operating conditions were optimized via the response surface methodology. Using the actual RO concentrate from a brackish water desalination plant as the feed solution for BMED after softening pretreatment, an acid of 0.7 mol/L and a base of 0.6 mol/L were produced in three BMED cycles, and the salt content in the feed compartment decreased from 19.8 to 4.1 g/L in each cycle. While the acid and base produced on site can be used for membrane cleaning and pH adjustment of the RO influent water, the residual salt solution from the BMED can be pumped to the RO system to maximize utilization of the water resources. The purities of the acid and base produced were 91.1 and 97.2%, respectively, and the total process cost was estimated at $1.69/kg NaOH.