| Summary: | Bioprocesses carried out for the production of fuels and other value-added co-products require effective process control strategies. The objective of this research is to apply Titrimetric Off-Gas Analysis (TOGA) for the on-line estimation of fermentation end products using Clostridium thermocellum. The hydrogen ion production, gaseous H2 and CO2, soluble H2 and CO2, as well as ethanol in the liquid phase and vapour phase, were monitored. All parameters, except the dissolved gases, showed good correlation with concurrent off-line analysis. The resulting mass and electron balances were close to theoretical values, and not significantly different from those determined using off-line analysis. Liquid-to-gas mass transfer limitations caused supersaturation of H2(aq) for a wide-range of operating conditions, and on average, ranged between 8-14 times the expected value at thermodynamic equilibrium. The supersaturation of CO2(aq) was conditional, and could be alleviated by increased sparging at agitation such that no significant mass transfer limitation was present. Simultaneous data on ethanol, CO2, and H2 could be obtained with the MIMS probe placed adjacent to the liquid surface in the reactor headspace. From this data, a metabolic model was proposed for the on-line estimation of formate and acetate using a mass balance and an electron balance. The model estimated formate concentrations with reasonable accuracy. Acetate predictions agreed with the qualitative trends, but the concentrations were inaccurate in comparison with off-line analysis. It was demonstrated that the sensor could provide on-line information on all major end-products synthesized by C. thermocellum. In conclusion, TOGA is a valuable instrument for the on-line monitoring and study of fermentation processes for cellulosic biofuels production
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