5-09: Development of novel biofilm-based reactor systems for enhancing mass transfer in syngas fermentation

Syngas fermentation is a promising technology for sustainable fuels and chemicals production. However, syngas conversion efficiency is limited by the low mass transfer efficiency, due to the low water-solubility of carbon monoxide and hydrogen. Bioreactor design plays an important role to enhance the mass transfer efficiency. In this study, we investigated the applicability of two biofilm-based reactor systems, hollow fiber membrane biofilm reactor (HFM-BR) and monolithic biofilm reactor (MBR), for mass transfer enhancement in syngas fermentation.  Clostridium carboxidivorans strain P7 was used as test strain. Both reactor systems were operated under batch condition for 15 days with continuous syngas feed at 200 mL/min so that microbes could attach onto the surface of hollow fiber membrane or monolith channels. The continuous operation was followed after the biofilm was established by continuously feeding liquid media the reactors. For HFM-BR system, the maximum ethanol concentration was found to be 24.3 g/L. For MBR system, two gas-liquid distributors (i.e. bubble column and nozzle spray) were used to obtain the even gas-liquid distribution in the monolith channels. In bubble column design, bubbles were generated from the wood gas-diffuser placed at bottom of the monolith. In nozzle spray design, syngas and liquid media was fed over the top of the monolith in co-current pattern using the packing bed type distributor. A conventional continuous stirred tank reactor (CSTR), which has the same working conditions as the above systems, was used for comparison in terms of cell growth, CO/H₂ consumption rate, and ethanol and acetate productivity.