Effects of biomass-generated syngas constituents on cell growth, product distribution and hydrogenase activity of clostridium carboxidivorans P7 T

Previous studies have demonstrated the fermentation of biomass-generated syngas produced in a fluidized-bed gasifier to obtain end products such as ethanol and acetic acid. The fermentation system utilized a novel bacterium, Clostridium carboxidivorans P7 T. Several effects of the syngas, as compared to “clean” gases of similar composition, were observed during the fermentation including 1) growth inhibition of cells after 1.5 days, 2) immediate cessation of hydrogen consumption, and 3) a burst of ethanol production and a decrease in acetic acid production.
Syngas typically contains CO, CO2, and H2 (along with N2 and methane in certain cases). The syngas for this study, which was obtained from Switchgrass, also contained other trace species such as ethane, ethylene, acetylene, and nitric oxide (NO). Tars like benzene and toluene (both volatile and particulate) were also identified. Several of these “contaminants” of syngas were tested to determine the cause of cell dormancy. Additional cleaning of the syngas via a 0.025 µm filter negated cell dormancy while studies with other gaseous contaminants showed no effect on cell growth. Analysis of the filter using a scanning electron microscope showed the presence of tar particulates, suggesting that tars inhibited the cell growth. Batch studies in the presence of tars showed a similar growth-inhibition, confirming the above hypothesis.