Flux balance analysis of mixed anaerobic microbial communities: Effects of linoleic acid (LA) and pH on biohydrogen production

The internal fluxes of mixed anaerobic cultures fed 2000 mg l⁻¹ linoleic acid (LA) plus glucose at 6 initial pH conditions and maintained at 37 °C were estimated using a flux balanced analysis (FBA). In cultures fed LA at pH 7, less than 8% of the flux was diverted to CH₄. At an initial pH ≥ 5.5, the quantity of glucose removed was greater than 95%; however, at pH 4.5 and 5.0 the quantity consumed were 38% and 75%, respectively. The FBA output showed that the acetogenic H₂-consumers were responsible for more than 20% of the H₂ consumed. Adding LA and decreasing the pH was ineffective in reducing the activity of acetogenic H₂-consumers. As the initial pH decreased, the acetogenic H₂-consuming flux decreased in the presence of 2000 mg l⁻¹ LA. A maximum H₂ yield of 1.55 mol mol⁻¹ glucose consumed (peak hydrogenase flux (R12)) was attained when the acetogenic H₂-consuming flux reached 0.42 mol at a pH of 5.5.