A critical review on biofilm-based reactor systems for enhanced syngas fermentation processes

For encouraging industrial growth based on sustainability, renewable energy sources as replacement of fossil fuels have gained a great importance worldwide. Syngas fermentation fulfills the requirements for sustainable bioenergy and biochemical productions. In comparison to other gas to biofuel conversion methods such as Fischer-Tropsch synthesis, it not only requires less energy owing to its low operating temperature and pressure, it also offers greater flexibility in terms of feedstock composition as well as variety of the end products. In addition, biological catalysts are capable of adopting presence of impurities in syngas whereas metal catalysts get deactivated. Lanzatech has successful commercial plants in operation utilising the CO rich off gas from the steel industry. However, low mass transfer rate in the gas-liquid interface is the major obstacle which renders widespread adoption and industrial applications of the process limited. Recent research data indicates the capability of the biofilm reactors on improving mass transfer rates as well as achieving greater process stability. This review collates the literature on impact of biofilm technology to provide new insights in syngas fermentation to guide future research towards commercialisation of renewable sustainable biofuels and biochemicals. In this regard, operation principles, economic perspectives and mass transfer mechanisms of various biofilm reactors are compared among each other as well as with the conventional reactor configurations. Current commercialisation stage of syngas fermentation is summarised along with pilot scale patent as the initiatives of future plants. Overall, operation challenges from both microbial and bioprocessing standpoint are highlighted, and potential solutions are provided.