Volatile fatty acids recovery from the effluent of an acidogenic digestion process fed with grape pomace by adsorption on ion exchange resins

The purpose of this work was to perform the preliminary development and optimization of a volatile fatty acid (VFA) separation process from an actual effluent of grape pomace acidogenic anaerobic digestion by ion exchange (IE) resins. Batch IE and desorption tests were performed with acetic acid, VFA synthetic mixtures and an actual digestate. The comparison of four amino IE resins led to the selection of Amberlyst A21, a tertiary amino resin characterized by a relatively low price and high IE performances. The latter increased by increasing VFA chain length, this suggesting a relevant contribution of physical adsorption for high molecular weight VFAs. The best IE performances were obtained at pH 3-4.5 in the presence of acetic acid alone, and at pH 6.5 with the actual digestate. Basified ethanol allowed a complete desorption of all the adsorbed VFAs. Solvent recovery by evaporation, obtained with negligible losses of the desorbed VFAs, allowed the production of a highly concentrated water solution of the recovered VFAs. This result represents a crucial feature for the development of innovative VFA-fed biotechnological processes such as polyhydroxyalkanoate production ones. A model taking into account VFA IE, the competitive effect exerted by other anions and the HCO3−/CO32− buffering effect that characterizes actual digestates led to a satisfactory prediction of the experimental data, and represents an effective tool to identify the optimal operational conditions. Overall, Amberlyst A21 represents an effective candidate for the development of an adsorption/desorption process for VFA recovery from the effluents of acidogenic fermentations.