Near-zero liquid discharge and reclamation process based on electrodialysis metathesis for high-salinity wastewater with high scaling potential

This study describes an emerging technology for near-zero liquid discharge desalination (ZDD) and salt reclamation using electrodialysis metathesis (EDM) to treat high-salinity wastewater with high scaling potential. Response surface methodology was employed to determine the optimal conditions for EDM-based ZDD process, and Box-Behnken center-united experimental design was used to quantify the effects of superficial velocity, applied voltage, and volume ratio of diluate/concentrate streams (Vc/Vd) on the salt removal ratio and current efficiency. These parameters influenced the outcome with the impacts following: voltage > superficial velocity > Vc/Vd, and the interactions were generally weak. The concentration of Na- and Cl-type liquid salts reached 200 and 170 g/L, respectively, after seven batch operations without scaling risks. Moreover, the two concentrate streams could be combined to precipitate CaSO4 with about 60% removal of Ca2+ via production of a solid byproduct. Alkali-assisted precipitation of the residual stream demonstrated efficient recovery of Mg2+ resources. Additionally, the purified solution could be further utilized to recover chemical resources (NaCl and Na2SO4) through a partial crystallization process. This work thus provides an applicable approach for the ZDD and reclamation of high-salinity wastewater with high scaling potential, which exist widely in seawater desalination engineering and industrial wastewater treatment.