Recovery and fractionation of volatile fatty acids from fermented solutions by electrodialysis: electrochemical characterization of anion-exchange membranes

Electrodialysis can be used to recover charged precursors, such as volatile fatty acids (VFAs), of the biopolymers polyhydroxyalkanoates (PHAs). In general, all VFAs are recovered in a receiver solution, despite their advantageous partial fractionation. Herein, the separation of acetic, propionic, butyric, and valeric acids by electrodialysis was evaluated using three anion-exchange membranes (namely, Ralex AMH-PES, Fumasep FAS-PET-130 and PC200D) applying cell voltages from 0 V to 2.88 V. The mass transfer mechanisms were evaluated by linear sweep voltammetry and chronopotentiometry. Fumasep showed a slightly greater VFAs fractionation capacity than Ralex, while it was much greater for PC200D due to the presence of tertiary amines in its fixed functional groups. Overall, increasing the operating voltage and/or time reduced the degree of VFAs fractionation with all membranes. The higher percent extraction values and greater VFAs fractionation degrees obtained with the PC200D membrane could enhance PHAs storage efficiency.