In-situ carboxylic acid separation from mixed-acid fermentation of cellulosic substrates in batch culture

Abstract

Using methane-arrested mixed cultures, organic substrates can be fermented to mixed carboxylic acids (i.e., C2 to C8 volatile fatty acids) via the carboxylate platform. A commercial example, the MixAlco® process recovers the carboxylic acids and transforms them to chemicals and fuels. To reduce product inhibition, ion-exchange resin (IR) fermentors used weak-base anion-exchange resins (Amberlite IRA-67) to recover carboxylic acids from fermentation broth and thereby maintain near-neutral pH. Control fermentors used magnesium carbonate (MgCO3) to buffer to near-neutral pH. Compared to the control, the IR fermentors increased acid yields by 2.2, 1.54, and 1.55 times for α-cellulose substrate, paper substrate, and lime-pretreated corn stover, respectively. Furthermore, extraction increased yields of valuable long-chain carboxylic acids. These results suggest further improvements are possible in advanced MixAlco® process configurations, such as countercurrent continuous fermentations.