Commercial Biomass Syngas Fermentation

Abstract

Abstract:The use of gas fermentation for the production of low carbon biofuels such as ethanol or butanol from lignocellulosic biomass is an area currently undergoing intensive research and development, with the first commercial units expected to commence operation in the near future. In this process, biomass is first converted into carbon monoxide (CO) and hydrogen (H 2 )-rich synthesis gas (syngas) via gasification, and subsequently fermented to hydrocarbons by acetogenic bacteria. Several studies have been performed over the last few years to optimise both biomass gasification and syngas fermentation with significant progress being reported in both areas. While challenges associated with the scale-up and operation of this novel process remain, this strategy offers numerous advantages compared with established fermentation and purely thermochemical approaches to biofuel production in terms of feedstock flexibility and production cost. In recent times, metabolic engineering and synthetic biology techniques have been applied to gas fermenting organisms, paving the way for gases to be used as the feedstock for the commercial production of increasingly energy dense fuels and more valuable chemicals.

Trash to treasure: production of biofuels and commodity chemicals via syngas fermenting microorganisms

“…As a proof of concept, the deletion of the bifunctional aldehyde/alcohol dehydrogenase in C. ljungdahlii resulted in increased acetate yield on the expense of ethanol [39 ]. The functionality of a construct harboring the known acetone pathway of C. acetobutylicum was demonstrated in C. aceticum, enabling the latter to produce 8 mg/L of acetone from a mixture of H 2 and CO 2 [11,57]. Similarly, plasmids bearing heterologous genes for the butanol synthesis pathway of C. acetobutylicum were introduced into C. ljungdahlii allowing for low levels of butanol production [21].…”

“…Among these limitations are low syngas kLa, low cell-biomass, sporulation, as well as substrate and product inhibition. Engineering syngas fermenting microorganisms for enhanced biofilm development can help overcome their inherently low biomass yield while enabling the use of reactors with enhanced gas mass transfer rates such as airlift reactors [59] or membrane biofilm reactors [60] as well as other types of biofilm-based reactors suitable for syngas fermentation [15,57]. More effective biofilms can be formed by increased exopolysaccharide production [61] or by manipulating other factors that are known to modulate biofilm formation in Clostridium species [62].…”

Rapid bio-methanation of syngas in a reverse membrane bioreactor: Membrane encased microorganisms

“…Anaerobic microorganisms, primarily acetogencs, carboxytrops, and methanogencs are able to use CO and/or CO 2 sources as carbon sources and use H 2 as an energy source for their metabolism and produce different bio-products (Daniell et al, 2012). Thus, the combination of thermal and biological processes for the conversion of feedstocks into biofuel has been explored.…”

Evidence for a Hexaheteromeric Methylenetetrahydrofolate Reductase in Moorella thermoacetica

“…When CO is used, ethanol and 2.3-butanediol can be major fermentation end products (2,3). Genetically engineered acetogens can also produce acetone, butanol, or other products of industrial interest (4)(5)(6).…”