Selective recovery of medium-chain fatty acids from secondary fermentation broth by flow-electrode capacitive deionization

Abstract

Medium-chain fatty acids (MCFAs) can be produced using precursors from anaerobic digestion, which have greater application potential than methane. However, MCFAs recovery is challenged by the high energy and/or reagent consumption. To bridge this gap, in this study, the feasibility was demonstrated using flow-electrode capacitive deionization (FCDI) technology for the recovery of MCFAs from secondary fermentation broth. Results showed that caproate was selectively recovered and adsorbed on the carbon materials, while acetate and butyrate were mainly recovered and dissolved in the anolyte. Under the optimal conditions, a high selectivity (51.6%) and recovery concentrations (9.26 ± 0.37 g/L) of caproate were achieved. Besides, catholyte in FCDI was used as an in-situ generated desorbent for MCFAs recovery, which could guide the process design. In addition, as a technical optimization, nickel foam as an alternative anode decreased Faradaic oxidation of carboxylates. Overall, this study demonstrated that FCDI could be served as a new separation and purification technology to facilitate valuable MCFAs recovery.