Evaluation of bipolar membrane electrodialysis for desalination of simulated salicylic acid wastewater

Salicylic acid (SA) is an important chemical raw material, but its production process generates large amounts of phenol-containing hypersaline wastewater. Bipolar membrane electrodialysis (BMED) technology was proposed to remove Na2SO4 from this wastewater and generate NaOH and H2SO4. The influences of initial pH in feed solution, current density, flow velocity, initial Na2SO4 concentration and volume ratio on the BMED process were investigated. These findings revealed that pH had no significant effect on the desalination rate, but affected the migration of organics including phenol and SA. When the input current density was 40 mA/cm2, flow velocity was 4.0 cm/s and the volume ratio was 2:1, the concentrations of H2SO4 and NaOH could reach the maximum at 0.97 mol/L and 1.56 mol/L respectively, with initial Na2SO4 concentration of 80 g/L and corresponding to a desalination rate of 96.3%. The current efficiency of acid was 55.2% and that of base was 50.2%, and energy consumption was 2.89 kWh/kg H2SO4 and 3.98 kWh/kg NaOH. These results confirmed BMED technology could treat simulated SA wastewater effectively and produce H2SO4 and NaOH. It provides a theoretical basis and guidance for the practical treatment of this type of wastewater.