(593h) Medium Design for Ethanol Production Through Syngas Fermentation

Biomass derived syngas (CO, H₂ and CO₂) can be fermented into ethanol using Clostridium ragsdalei.  The use of low cost medium is critical to make syngas fermentation commercially viable.  Elimination and reduction in concentrations of expensive nutrients such as morpholinoethane sulfonic acid (MES) buffer and yeast extract (YE) from the medium were examined.  Syngas fermentations were done in 250 ml bottles at 37^oC using 20 CO: 15 CO₂: 5 H₂ mol% syngas mixture.  The syngas was supplied to cells every 24 h for 15 days.  Samples were collected every 24 h and analyzed for pH, cell mass, product concentrations and gas utilization.  Results showed that MES buffer can be completely removed from the medium and pH can be maintained at desired values using sodium bicarbonate.  YE was necessary for C. ragsdalei cell growth; however, lower YE concentrations preferentially generated more ethanol.  A defined medium was designed in which YE and MES were eliminated and concentrations of minerals and trace metals were adjusted.  Cell growth was slow in the defined medium without YE; however, ethanol production was comparable in both media.  The cost of the defined medium was less than one third that of the YE medium.  The feasibility of alternative nutrients to replace YE will be presented.  The cost of the developed defined medium was reduced by 97% compared to the standard YE medium with MES, offering significant cost benefits for potential industrial ethanol production.