Co-fermenting lactic acid and glucose towards caproic acid production.

The functional role of lactate (H), as a co-substrate along with glucose (Glu) as well as an electron donor for the synthesis of caproic acid (H), a medium chain fatty acid (MCFAs) was studied. A varied H and Glu ratios were thus investigated in fed-batch anaerobic reactors (R1-R5) operated at pH 6 with a heat-treated anaerobic consortium. R1 and R5 were noted as controls and operated with sole Glu and H, respectively. Strategically, ethanol (H) was additionally supplemented as co-electron donor after the production of short chain carboxylic acids (SCCAs) for chain elongation in all the reactors. The reactor operated with H and Glu in a ratio of 0.25:0.75 (1.25 g/L (H) and 3.75 g/L (Glu)) showed the highest H production of 1.86 g/L. R5 operated with solely H yielded propionic acid (H) as the major product which further led to the higher valeric acid (H) production of 1.1 g/L within the reactor. Butyric acid (H) was observed in R1, which used Glu as carbon source alone indicating the importance of H as electron co-donor. Clostridium observed as the most dominant genera in shotgun metagenome sequencing in R2 and R3, the reactors that produced the highest H in comparison to other studied reactors. The study thus provided insight into the importance of substrate and electron donor and their supplementation strategies during the production of MCFAs.