Bacteria can metabolise sugars in milk or wheat into wondrous forms like sourdough bread, sauerkraut, beer and cheese. Modern industrial fermentation uses similar techniques: it cultivates biochemicals in the bodies of microorganisms for drugs, proteins, nutraceuticals, and personal care chemicals.
Already, fermentation technology allows us to replace petrochemical inputs with organic feedstock for a vast range of goods. However, new feedstocks could be about to bolster its sustainability credentials further.
Right now, the fermentation industry feeds microbes on food waste, paper waste, farming waste, or plant crops. The microbes break these organic feedstocks into sugars and the sugars into the target chemical plus carbon.
Another form of fermentation reverses the process: rather than starting with sugars then ending up with high value chemicals, microbes eat carbon dioxide or other gases and turn them into sugars and high value chemicals. This is known as gas fermentation or autotrophic fermentation.
For years, scientists have known that carbon and other gases can offer a cost-effective, abundant feedstock for microbial fermentation but commercialisation is only just starting.
Carbon dioxide has been attracting the most attention as a new generation fermentation feedstock because of its obvious climate mitigation uses but other suitable gases include
methane, formate, methanol, acetate, and ethanol – some of which are eco-toxic, low-value industrial byproducts.
Drawing down environmentally harmful gases for high-value manufacturing could contribute to climate mitigation goals while using gas over biomass could cut back on the need to use resource-intensive crops for chemical raw materials.
Right now, progress in gas fermentation technologies is roughly evenly divided between academia and industry. Commercialisation is just beginning and researchers across both sectors are still finding ways to diversify the suite of functional gas-eating microbes and make them produce chemicals efficiently.
The feedstock problem in fermentation today
Gas fermentation addresses the problems of existing industrial fermentation pathways. Already, fermentation biomanufacturing offers a more sustainable manufacturing route to consumer chemicals but certain issues remain.
Because it avoids petrochemical feedstock or eco-toxic synthetic compounds, fermentation biomanufacturing has been trapped as a way of greening the chemicals industry and reducing its reliance on oil through exploiting renewable inputs and live organisms as the mechanisms to create consumer compounds.
However, one factor that is undercutting the sustainability profile of the fermentation industry as it exists today is the source and nature of its organic feedstock.
Cultivated feedstocks, which are common in the industry today, are the most environmentally problematic aspect of modern fermentation. Most of the industry draws on sugarcane, sugar beet, maize (corn), and sorghum as sugar sources for their process.
These are all human foods and require lots of land, meaning they can reduce the area available to make crops for human food and rack up the carbon intensity of the final product through use of agricultural fertiliser.
There are more sustainable options. Some biorefineries use waste byproducts from farms as microbial feedstocks. These are limited, variable resources and there can be logistical and cost barriers to collecting them.
Lanzatech extends gas fermentation from biofuels to industrial chemicals
Lanzatech is the biggest gas fermentation company, using carbon monoxide to mainly produce ethanol aviation fuels. It styles itself as a carbon recycling technology company which uses bacteria to turn waste gas into fuel.
The Illinois-based company was formed in 2005 and in 2022 announced plans to go public through a deal with AMCI Acquisition Corp, which will unlock $275 million for the company and raise its valuation to $2.2 billion.
The company primarily draws its carbon monoxide gas feedstock from steel mill waste gases, locating their operations at major steel works in New Zealand, China, and Taiwan. The first commercial use of their jet fuel from steel emissions was used in a Virgin Atlantic flight in 2018.
At the moment, only a few chemical products can be obtained efficiently via gas fermentation methods. Microbes that are capable of consuming gases are not particularly fast or efficient at assimilating carbon to make any chemical except biofuels.
Other high value chemicals, such as those used in personal care, are not being produced in large amounts commercially at the moment through gas fermentation.
However, Lanzatech is now branching out beyond the aviation industry. In February 2022, it announced it had conducted a pilot demo on producing waste carbon into either acetone or IPA, basic precursors for thousands of products across multiple industries including fabrics, materials, and cosmetics.
These new gas fermentation products were achieved by rewiring the microbe they use in ethanol fuel production, C. autoethanogenum, to produce acetone and IPA as well.
The demo, published in Nature biotechnology, concluded that the life cycle emissions of Lanztech’s gas gemented acetone and IPA were negative, meaning the whole fermentation process drew down more carbon from the atmosphere than it released it. The study also said that the approach can be “readily adapted to a wide range of commodity chemicals”.
Lanzatech’s feedstock is carbon monoxide, not carbon dioxide. However, the company’s new process for making acetone and IPA could draw on carbon dioxide, said CEO Jennifer Holmgren, is the hydrogen is also given to the microbes to consume.
The company is now expanding its partners in the consumer-facing chemicals industry. Its gas fermentation process was the technology behind Swiss sports brand’s Cloudprime shoe containing a foam made from carbon emissions.
The company’ previous partnerships will also open doors for the consumer industrial chemicals market, like the supply partnership it has had with L’Oreal since 2020 supplying ethanol-based polyethylene.
Other gas fermentation players today
Lanzatech is the biggest gas fermenting company in the world, producing 90, 000 tonnes a year but smaller players are now targeting the technology.
Nottingham University’s Synthetic Biology Research Centre (SBRC), a centre of gas fermentation research, has given rise to two startups in gas fermentation bio-manufacturing: Deep Branch and PhaseBio.
Deep Branch was founded by three former SBRC PhD students and makes sustainable animal feed from waste carbon dioxide gas, raising over €8m to build a pilot plant for FishKind single-celled protein.
Unlike gas fermentation giant Lanzatech, this startup uses carbon dioxide rather than monoxide, in conjunction with hydrogen and oxygen. The microbes feed on these gases plus electrolyte, dried, and then processed into a single cell protein.
PhaseBio was founded in 2020 and is converting industrial waste carbon dioxide into chemicals and fuels. Like Deep Branch, their feedstock is carbon dioxide and hydrogen, as opposed to the carbon monoxide used by Lanzatech.
Like Lanzatech, PhaseBio’s approach is to set up their fermentation technology on the site of polluting industries, capturing their waste and turning it into high value goods.
There are a few challenges before more wide scale commercialisation can happen. The biggest issue in the way of scaling is how to make carbon-eating microbes and yeasts consume and process the gas more quickly. Gene editing is now helping push higher productivity in acetogen microbes(#1).
Like all industrial fermentation, the practical challenges are immense: the manufacturers have to consider feedstock cost versus the market value of the eventual biochemical and how to make adverse products from a single process.
Reactor design is important in viability. Optimising Mass transfer, the movement of gases into the liquid, is one of the biggest limiting factors in upping productivity in gas fermentation. To keep overall costs down, means of achieving mass transfer will have to be energy efficient.
The uses and abuses of gas fermentation
If gas fermentation technology is improved, it would open up a vast new resource pool for the fermentation industry. Cheap carbon dioxide could be taken from steel and cement production to create industrially valuable chemicals. The next step for the industry will be making governments aware of the potential for gas fermentation to replace petrochemical industry and heighten its profile as a potential geren industry.
A close eye should be kept on the uses to which gas fermentation is put so that it does not become a tool to justify the continuation of a carbon-based economy. There is a disquieting possibility that this technology may give licence to carbon fuel-reliant industries to continue using petrochemicals if they use biobased carbon capture in some of their operations.
The carbon mitigating power of gas fermentation may also be enhanced if it is focused on making industrial chemicals rather than car fuels. Cars need repeated stocks of fuel, extending the carbon emissions through its whole operating life. Chemicals and materials are better ways to exploit the sustainability potential of gas fermentation technology as there are no operating emissions once these goods have been made.
#1. (1)Jia D., He M., Tian Y., Shen S., Zhu X., Wang Y., Zhuang Y., Jiang W., Gu Y. Metabolic engineering of gas-fermenting Clostridium ljungdahlii for efficient co-production of isopropanol, 3-hydroxybutyrate, and ethanol. ACS Synth. Biol. 2021;10:2628–2638. doi: 10.1021/acssynbio.1c00235. [PubMed] [CrossRef] [Google Scholar](2) Liew F.E., Nogle R., Abdalla T., Rasor B.J., Canter C., Jensen R.O., Wang L., Strutz J., Chirania P., de Tissera S., et al. Carbon-negative production of acetone and isopropanol by gas fermentation at industrial pilot scale. Nat. Biotechnol. 2022;40:335–344. doi: 10.1038/s41587-021-01195-w.