Low-Carbon Fuel and Chemical Production by Anaerobic Gas Fermentation

Abstract

World energy demand is expected to increase by up to 40% by 2035. Over this period, the global population is also expected to increase by a billion people. A challenge facing the global community is not only to increase the supply of fuel, but also to minimize fossil carbon emissions to safeguard the environment, at the same time as ensuring that food production and supply is not detrimentally impacted. Gas fermentation is a rapidly maturing technology which allows low carbon fuel and commodity chemical synthesis. Unlike traditional biofuel technologies, gas fermentation avoids the use of sugars, relying instead on gas streams rich in carbon monoxide and/or hydrogen and carbon dioxide as sources of carbon and energy for product synthesis by specialized bacteria collectively known as acetogens. Thus, gas fermentation enables access to a diverse array of novel, large volume, and globally available feedstocks including industrial waste gases and syngas produced, for example, via the gasification of municipal waste and biomass. Through the efforts of academic labs and early stage ventures, process scale-up challenges have been surmounted through the development of specialized bioreactors. Furthermore, tools for the genetic improvement of the acetogenic bacteria have been reported, paving the way for the production of a spectrum of ever-more valuable products via this process. As a result of these developments, interest in gas fermentation among both researchers and legislators has grown significantly in the past 5 years to the point that this approach is now considered amongst the mainstream of emerging technology solutions for near-term low-carbon fuel and chemical synthesis.

Anaerobes in Industrial- and Environmental Biotechnology

“…Fermentation of syngas (containing CO, CO 2 , and H 2 ), produced from biomass or fossil feedstocks, described in [9], is an important example of the microbial route for conversion of gas mixtures to a variety of products. Several strictly anaerobic acetogenic bacteria belonging to Proteobacteria, Planctomycetes, Spirochaetes, and Euryarchaeota (e.g., certain Acetobacterium spp., Clostridium spp., Desulfobacterium spp., Eubacterium spp., and Moorella spp.)…”

“…Several strictly anaerobic acetogenic bacteria belonging to Proteobacteria, Planctomycetes, Spirochaetes, and Euryarchaeota (e.g., certain Acetobacterium spp., Clostridium spp., Desulfobacterium spp., Eubacterium spp., and Moorella spp.) are capable of syngas/CO 2 fermentation using the reductive acetyl-CoA pathway or Wood-Ljungdahl (WL) metabolic pathway to acetate [9,73,74]. Electrons required for the metabolic process are obtained from H 2 via the hydrogenase enzyme and/or from CO via the CO dehydrogenase enzyme:…”

“…Although Lanza Tech has developed syngas fermentation based on the WL pathway for commercial scale production of ethanol [9], Evonik uses a CO 2 -based acetone fermentation process in which the acetogens are genetically modified to divert the acetyl-CoA from the WL pathway to acetone via acetoacetyl-CoA and acetoacetate [75]. Recently, Moorella thermoacetica, a thermophilic acetogenic bacterium which produces acetic acid as the only end product of the WL pathway, was used in a bubble column reactor for conversion of syngas to acetic acid with improved productivity [76].…”

“…In the current trend in shift from fossil-based to biobased economy, anaerobes are attracting increasing interest as tools for transformation of renewable resources such as biomass and gases (e.g., synthesis gas [9] into diverse chemicals and both liquid (this chapter and [9]) and gaseous biofuels [3,4]. They serve as sources for enzymes catalyzing the degradation of complex biomass or the uptake of gases such as CO, CO 2 , and H 2 , and of metabolic pathways for different products in both wild type and engineered microbial hosts.…”

A Prospective Study on the Fermentation Landscape of Gaseous Substrates to Biorenewables Using Methanosarcina acetivorans Metabolic Model

“…Acetogens has been the workhouse for gas fermentation in industry for over two decades. Anaerobic conversion of carbon monoxide into valuable products such as ethanol, acetate, and 2,3-butanediol at industrial scale has been pursued using different strains of Clostridium (Simpson et al, 2010; Köpke et al, 2011a,b; Tran and Simpson, 2015; Daniell et al, 2016; Martin et al, 2016). A recent study on the co-utilization of carbon dioxide and carbon monoxide or hydrogen to produce acetate using Moorella thermoacetica (Hu et al, 2016) further demonstrates the need for systematic study of co-utilization of various C 1 gases in other potential microbial hosts.…”