Gas Fermentation—A Flexible Platform for Commercial Scale Production of Low-Carbon-Fuels and Chemicals from Waste and Renewable Feedstocks

Abstract

There is an immediate need to drastically reduce the emissions associated with global fossil fuel consumption in order to limit climate change. However, carbon-based materials, chemicals, and transportation fuels are predominantly made from fossil sources and currently there is no alternative source available to adequately displace them. Gas-fermenting microorganisms that fix carbon dioxide (CO2) and carbon monoxide (CO) can break this dependence as they are capable of converting gaseous carbon to fuels and chemicals. As such, the technology can utilize a wide range of feedstocks including gasified organic matter of any sort (e.g., municipal solid waste, industrial waste, biomass, and agricultural waste residues) or industrial off-gases (e.g., from steel mills or processing plants). Gas fermentation has matured to the point that large-scale production of ethanol from gas has been demonstrated by two companies. This review gives an overview of the gas fermentation process, focusing specifically on anaerobic acetogens. Applications of synthetic biology and coupling gas fermentation to additional processes are discussed in detail. Both of these strategies, demonstrated at bench-scale, have abundant potential to rapidly expand the commercial product spectrum of gas fermentation and further improve efficiencies and yields.

Arginine deiminase pathway provides ATP and boosts growth of the gas-fermenting acetogen Clostridium autoethanogenum

“…industrial waste gases, syngas (CO/CO 2 and H 2 ) and methane (Bertsch and Müller, 2015;Daniell et al, 2012;Dürre and Eikmanns, 2015;Köpke et al, 2011;Latif et al, 2014;Liew et al, 2016b). Production of fuels and chemicals via gas fermentation does not compete for arable land and food resources, in contrast to using farmed sugars as feedstock.…”

“…From the many acetogens, Clostridium autoethanogenum is a promising gas-fermenting biocatalyst used at industrial scale (Liew et al, 2016b). C. autoethanogenum natively produces acetate, ethanol, 2,3-butanediol and lactate as by-products of growth (Abrini et al, 1994;Köpke et al, 2011;Marcellin et al, 2016).…”

Biofuels and Biochemicals Production

“…The lower lignin content increased the cellulose available for subsequent processing and conversion to around 66-69%, allowing to obtain 69% ethanol yields during the fermentation process. Microbial delignification was also studied with P. ostreatus on H 2 O 2 -pretreated rice hull [57]. This pretreatment combination increased the delignification range about two times, leading to 49.6% of glucose yield in the subsequent saccharification step.…”

“…However, the majority of gas consumed provides energy for cell function, resulting in the accumulation of acetic acid and ethanol. The Wood-Ljungdahl pathway for the production of ethanol and acetic acid; THF: tetrahydrofolate; ACS: acetyl CoA synthase; CODH: carbon monoxide dehydrogenase; H 2 ase: hydrogenase; NADPH: reduced nicotinamide adenine dinucleotide phosphate; adapted from [1,57].…”

Syngas Fermentation: A Microbial Conversion Process of Gaseous Substrates to Various Products

“…A positive ΔG° for a Figure 2. The Wood-Ljungdahl pathway for the production of ethanol and acetic acid; THF: tetrahydrofolate; ACS: acetyl CoA synthase; CODH: carbon monoxide dehydrogenase; H 2 ase: hydrogenase; NADPH: reduced nicotinamide adenine dinucleotide phosphate; adapted from [1,57].…”