Separation of NaCl and humic substances in anion exchange spent brine with electrodialysis

The advanced treatment process of anion exchange can be an effective approach for removing dissolved organic matter in the drinking water, but the production of anion exchange spent brine is a main drawback. Herein, electrodialysis (ED) was used to separate high-concentration NaCl and humic substances (HSs) from anion exchange spent brine. The composition and characteristics of anion exchange spent brine were systematically studied, and the impacts of ion exchange membrane type, volume ratio of initial concentrate to dilute (Vc,0/Vd,0) and flow rate on the performance of lab-scale and pilot-scale ED were investigated. Our results demonstrated the cost-effective membrane pair was TWEDC1/TWEDA1 to treat anion exchange spent brine with high degree of aromaticity and plentiful oxygen-containing functional groups, because of its special membrane structure and membrane properties. High current efficiency of 90.60% and low energy consumption of 0.91 kW h/kg NaCl were achieved by ED with TWEDC1/TWEDA1. When Vc,0/Vd,0 was 1:4, 15% (w/w) recovery NaCl solution concentrated by lab-scale first-stage ED could be used as resin regeneration agent. Furthermore, lab-scale and pilot-scale two-stage ED were simultaneously verified to effectively separate NaCl and HSs in the anion exchange spent brine.