Biological conversion of carbon monoxide to ethanol: Effect of pH, gas pressure, reducing agent and yeast extract

A two-level full factorial design was carried out in order to investigate the effect of four factors on the bioconversion of carbon monoxide to ethanol and acetic acid by Clostridium autoethanogenum: initial pH (4.75–5.75), initial total pressure (0.8–1.6 bar), cysteine–HCl·H2O concentration (0.5–1.2 g/L) and yeast extract concentration (0.6–1.6 g/L). The maximum ethanol production was enhanced up to 200% when lowering the pH and amount yeast extract from 5.75 to 4.75 g/L and 1.6 to 0.6 g/L, respectively. The regression coefficient, regression model and analysis of variance (ANOVA) were obtained using MINITAB 16 software for ethanol, acetic acid and biomass. For ethanol, it was observed that all the main effects and the interaction effects were found statistically significant (p < 0.05). The comparison between the experimental and the predicted values was found to be very satisfactory, indicating the suitability of the predicted model.