(621f) Biological Alcohol Production from CO2 using Novel Acetogens

The conversion of CO₂ to valuable products such as alcohols can create additional revenues from industrial waste streams, while reducing greenhouse gas emissions. Acetogens such as Clostridium ragsdalei, C. carboxydivorans and C. ljundahlii have been used to convert syngas components (CO, CO₂ and H₂) into alcohols and organic acids via the acetyl-CoA pathway. However, few studies have focused on the use of these microorganisms to convert CO₂ to various products. In order to use CO₂ as a carbon source, an energy source such as H₂ must be present to allow the microorganism to reduce CO₂ into products. In the current study, C. ragsdalei strain P11, C. carboxidivorans strain P7A and three new clostridial strains A, B and C were used to convert CO₂ and H₂ into carboxylic acids and alcohols. Fermentations were performed in 250-mL bottle assays with 50 mL working volume at 37°C and 150 rpm. A gas mix containing H₂:CO₂:N₂ (60:20:20) was fed daily for 360 h. Results showed that all strains grew on CO₂ and produced alcohols and organic acids. However, strains P11 and P7A grew faster and consumed more CO₂ and H₂ compared to the other new strains. There was a lag phase of 48 to 72 h for strains A, B and C. Strains P11 and P7A produced more organic acids than the new strains. However, preliminary results showed that the new strains appear to make more C4 and C6 products compared to strains P11 and P7A. The effects of fermentation parameters such as gas composition and pressure will be presented. Further adaption and improvement of the five strains to reduce lag phase and improve CO₂ and H₂ conversion to alcohols are needed to enhance their potential use in the conversion of CO₂ containing waste streams to biofuels.