Simultaneous regeneration of inorganic acid and base from a metal washing step wastewater by bipolar membrane electrodialysis after pretreatment by crystallization in a fluidized pellet reactor

This study aims to investigate the feasibility of an integrated system consisting of a fluidized pellet reactor and bipolar membrane electrodialysis (EDBM) for regeneration of acid and base from wastewater with a high concentration of calcium and nickel ions. The fluidized pellet reactor was used to reduce the potential of scaling on the membranes by crystallization. EDBM was applied to regenerate acid/base from this pretreated wastewater. The results show that calcium and nickel can be removed by the fluidized pellet reactor with sufficient efficiency (74% and 73% without filtration, 74% and 94.4% with filtration, respectively). After pretreatment, it was feasible to regenerate mixed acid and base using EDBM. The current efficiency was 69% for the acid, 80% for the base; the energy consumption was 5.5 kW h/kg acid and 4.8 kW h/kg base at a current density of 60 mA/cm2 and an initial concentration of 0.2 N. In a long-term experiment, the pretreatment increased cation exchange membrane performance and a high concentration of acid and base up to 1.76 N and 2.41 N was produced with only slight scaling on the cation exchange membrane surface. This integrated process is not only technically but also environmentally feasible, reducing water pollution and yielding valuable products to achieve sustainable development.