Conversion of biomass-generated syngas into next-generation liquid transport fuels through microbial intervention: potential and current status

The production of biofuels from synthesis gas that utilizes a wide variety of biomass is an emerging concept, particularly with the focus on biomass-based economy. Biomass is converted to synthesis gas via gasification, which involves partial oxidation of the biomass at high temperature. This route of ethanol or liquid biofuel production has the advantage of utilizing the entire biomass, including the lignin content. Though the technology is yet to be established, there is a major breakthrough in understanding the microbial route of synthesis gas conversion. Acetogenic microorganisms such as Clostridium ljungdahlii, Clostridium aceticum, Acetobacterium woodii, Clostridium carboxidivorans and Clostridium autoethanogenum have already been reported to play a role in the conversion of synthesis gas to ethanol and acetic acid. Poor mass transfer properties of the gaseous substrates and low ethanol yield from these biocatalysts are the major challenges, preventing the commercialization of synthesis gas fermentation technology. This article reviews the existing literature on biomass-derived synthesis gas fermentation into biofuels, specifically ethanol. Special emphasis has been laid on understanding the need of synthesis gas fermentation and its bioconversion into next-generation liquid transport fuels. However, advantages of microbial process over conventional methods and the role of different microorganisms and pathways used have also been described. The article also outlines the challenges and future research directions regarding up scaling and commercialization of synthesis gas fermentation technology.