A closed-loop integrated process of bipolar membrane electrodialysis and resin adsorption for resource recovery from high-salinity phenolic wastewaters: Salicylic acid manufacturing wastewater as a representative

Phenolic compounds stand as consequential chemical precursors, boasting an extensive array of industrial applications. The worldwide yield of such compounds attained 17 million tons annually, and a substantial volume of effluent characterized by elevated phenolics content along with inorganic salinity was emanated from the manufacturing processes, which would exert profound deleterious impacts upon the ecosystem and aquatic environment. Scant literature was available regarding efficacious treatment of these high-salinity phenolic wastewaters and complete recovery of its constituents currently. In this study, initially, various high-salinity phenolic wastewaters were treated in bipolar membrane electrodialysis (BMED) system, and the migration behavior of constituents was investigated. Drawing upon the migration patterns and the efficacy of BMED, a closed-loop integrated process of BMED and resin adsorption was proposed to thoroughly address this kind of wastewater and attain comprehensive material reclamation. Because of the wide use of salicylic acid (SA) all over the world, the enormous production in China, and the complexity of the sewage which contained rich Na2SO4, phenol, and SA from manufacturing process, SA manufacturing wastewater was selected as the representative sample. For the BMED process, the desalination rate got 99.4 % under the optimum conditions. The concentrations of H2SO4 and NaOH obtained were 0.56 and 0.78 mol/L. The preliminary separation of phenol and SA was realized during desalination. Then, the effluent of BMED feed compartment was injected into two-stage resin unit. The satisfactory regeneration of both spent resins was achieved, and high-purity phenol and SA were obtained. No contaminants were undetected in the effluent, allowing for the reuse of the effluent within BMED. The complete resource utilization of SA manufacturing wastewater was realized, indicating the viability of proposed integrated process for treating and resource recovering of analogous high-salinity industrial phenolic wastewater.