초록
Gasification-fermentation is a thermo chemical-biological process for the production of fuels and chemicals. Producer gas cleanup is a major issue that must be addressed for integration of these platforms. Pre-adaptation of producer gas fermenting microbes to gas impurities has improved tolerances to impurities and production of alcohols in certain bacteria. In this research, the effect of switchgrass generated producer gas was studied with adapted and unadapted cultures of C. ragsdalei and compared to fermentations with a control of clean custom producer gas. Results indicated no inhibition to microbial growth with unadapted cells and final cell mass concentrations were 22% higher when cells were exposed to switchgrass-based producer gas compared to control. The ethanol productivity with adapted cells was 1.9 and 2.8 times higher than unadapted and control treatments, respectively. Similarly, the ethanol yield (<TEX>$Y_{ETOH/X}$</TEX>) of C. ragsdalei adapted to producer gas was 119% more than the control and 35% greater than the unadapted cells used in this study. The presence of switchgrass-based producer gas also induced metabolic shifts resulting in reduction of acetic acid to ethanol that increased ethanol to acetate ratios from 0.7 g/g in control to 4.9 g/g with unadapted cells and 13.7 g/g with adapted cells. Isopropanol was also observed as a product when switchgrass generated producer gas was used. We conclude that cultural adaptation of C. ragsdalei to biomass generated producer gas during preculture stages could be used as an important strategy to enhance ethanol yields for integrating gasification and fermentation platforms using C. ragsdalei.