Comparison of ion removal from waste fermentation effluent by nanofiltration, electrodialysis and ion exchange for a subsequent sulfuric acid recovery

Abstract

Nutrient recovery from wastewater in the form of acids/bases by electrodialysis with bipolar membranes or diffusion dialysis facilitates the current demand for a green economy and circular production. However, bipolar membranes are sensitive to scaling, mainly by calcium and magnesium salts, as well as to biofouling caused by microbial growth and linked aspects. This work aimed to reduce divalent cations to a value below 10 ppm and DOC content of a residual liquid waste stream after microbial fermentation and before a bipolar electrodialysis/diffusion dialysis step for nutrient and acid/base recovery. In this context, three pretreatment technologies were analyzed: nanofiltration, electrodialysis with monovalent cation-exchange membranes, and ion-exchange resins. Nanofiltration and electrodialysis with monovalent cation-exchange membrane were demonstrated to be suitable pretreatments with 92–96 % Mg2+ and Ca2+ removal and 86–94 % DOC removal. Ion-exchange resins had excellent divalent cation removal but no DOC removal, therefore requiring additional treatment to remove organic substances and prevent membranes’ biofouling. Electrodialysis with monovalent cation-exchange membranes was preferable over nanofiltration due to the 1.6-fold concentration factor for sulfate ions. In contrast, nanofiltration had lower energy consumption and higher stability in divalent cation rejection. Results obtained in this study are valuable for selecting an appropriate treatment for resource recovery and water reclamation from industrial wastewater and for biotechnological downstream processes.