1.1. Bioreactor design

An optimum gas fermentation system requires efficient mass transfer of gaseous substrates to the culture medium (liquid phase) and microbial catalysts (solid phase). Gas-to-liquid mass transfer has been identified as the rate-limiting step and bottleneck for gas fermenta­tion because of the low aqueous solubility of CO and H2 respectively at only 77% and 68% of that of oxygen (on molar basis) at 35oC [185]. Hence, a bioreactor design that delivers suf­ficient gas-to-liquid mass transfer in an energy-efficient manner at commercial scale for gas fermentation represents a significant engineering challenge. A brief overview of reactor con­figurations reported in gas fermentation operations is given below.