| Scope and method of study. The purpose of this study was to investigate the performance of a microbial process to convert synthetic blends of syngas to ethanol using a recently discovered bacterium, P7. In view of the limited knowledge available in syngas fermentations, the research was targeted on investigating some of the critical engineering issues. The characteristics of the process, such as cell stability, intrinsic kinetic parameters, overall limiting mechanism, response to process perturbations, process enhancement methods were studied using several bioreactor configurations.; Findings and conclusions. Maintaining sodium sulfide concentration (0.1–1 ppm) was essential for cell stability of P7 in the bioreactor. The controlling step for the overall process was the availability of liquid nutrients to the bacterial cells. Intrinsic kinetic parameters for the bacterium were determined. The effects of various process conditions, such as, dilution rate of liquid nutrients, concentrations of trace metal solution, pH and temperature, gas phase compositions of CO2 on P7 were determined. Process enhancement techniques, such as, introduction of Hs in the feed gas, cell recycle, and screening of nutrients were performed to improve the cell and ethanol productions in the bioreactor. Future works required to improve the process performance were identified. |
