Diverting Electron Fluxes to Hydrogen in Mixed Anaerobic Communities Fed with Glucose and Unsaturated C18 Long Chain Fatty Acids

Hydrogen $\left({\text{H}}_2\right)$ production was maximized and methane $\left({\text{CH}}_4\right)$ formation was minimized in a mixed anaerobic culture which was maintained at $21°\text{C}$ and fed glucose plus unsaturated long chain fatty acids (LCFAs). The initial pH in the batch reactors was $7.8\pm 0.2$ . The two LCFAs under consideration included linoleic acid (LA) (two $\text{C}\text{C}$ bonds) and oleic acid (OA) (one $\text{C}\text{C}$ bond). Hydrogen production was observed when glucose was injected on Day 0 and again after Day 4. The ${\text{H}}_2$ yield in cultures fed LA was less than those receiving OA. The ${\text{H}}_2$ yield reached a maximum of approximately $1.1\text{mol}{\text{H}}_2{\text{mol}}^{-1}$ glucose when the LA level was $2,000\text{mg}{\text{L}}^{-1}$ . In the case of OA, a maximum yield of $1.3\text{mol}{\text{H}}_2{\text{mol}}^{-1}$ glucose was attained with $2,000\text{mg}{\text{L}}^{-1}$ . The inhibition caused by the addition of LA or OA diverted a fraction of electrons toward proton reduction. Under maximum ${\text{H}}_2$ production conditions in the LA fed cultures the acetate production pathway was repressed, while in cultures fed OA the acetate pathway was dominant. The amount of ${\text{CH}}_4$ produced decreased with increasing ${\text{H}}_2$ production and the major volatile fatty acids detected were acetate, propionate and butyrate. Small quantities of formate were detected only in cultures fed LA after the first glucose injection. As the LCFA concentration increased, the initial glucose degradation rate decreased.