Bacteria can metabolize the sugars in milk or wheat into wonderful forms such as yeast bread, sauerkraut, beer and cheese. Modern industrial fermentation uses a similar technology: it cultivates biochemicals in microorganisms for use in drugs, proteins, nutraceuticals and personal care chemicals.
Fermentation technology has already enabled us to replace petrochemical feedstocks with organic feedstocks for a wide range of products. However, new feedstocks may further enhance their sustainability credentials.
Currently, the fermentation industry uses food waste, waste paper, agricultural waste or plant crops as microbial feed. Microorganisms break down these organic feedstocks into sugars, which are broken down into target chemicals and carbon. Another form of fermentation reverses the process: instead of starting with sugar and ending with a high-value chemical, the microorganisms eat carbon dioxide or other gases and then convert them into sugar and high-value chemicals. This is called gaseous or autotrophic fermentation.
For years, scientists have known that carbon and other gases can provide cost-effective and abundant feedstocks for microbial fermentation, but commercialization is just beginning.
Carbon dioxide is attracting attention as a next-generation fermentation feedstock for its obvious climate mitigation uses, but other suitable gases include methane, formate, methanol, acetate, and ethanol-some of which are low-value industrial byproducts that are ecotoxic.
Reducing environmentally harmful gases for high-value manufacturing industries may contribute to climate mitigation goals, while using natural gas rather than biomass could reduce the need to use resource-intensive crops to produce chemical raw materials.
Currently, advances in gas fermentation technology are roughly equally divided between academia and industry. Commercialization is just beginning, and researchers in both fields are still searching for ways to diversify functional gas-feeding microorganisms and make them effective in the production of chemicals.
Feedstock issues in today's fermentation
Gas fermentation solves the problems of existing industrial fermentation pathways. Fermentative biomanufacturing has provided a more sustainable manufacturing pathway for consumer chemicals, but certain problems remain.
Because fermentative biomanufacturing avoids the use of petrochemical feedstocks or ecotoxic synthetic compounds, it has emerged as a way to green the chemical industry and reduce dependence on petroleum by utilizing renewable feedstocks and living organisms as a mechanism for producing consumer compounds.
However, one factor that undermines the sustainability of today's fermentation industry is the source and nature of its organic feedstock.
Commonly cultured feedstocks in today's industry are the most environmentally problematic aspect of modern fermentation. Most industries utilize sugarcane, sugar beets, corn, and sorghum as sources of sugar for their processes.
These are human foods and require large amounts of land, which means they can reduce the area available for growing human food crops and increase the carbon intensity of the final product through the use of agricultural fertilizers. There are more sustainable options. Some biorefineries use waste by-products from farms as microbial feedstock. These resources are limited and variable, and there may be logistical and cost barriers to collecting them.
Lanzatech Expands Gas Fermentation from Biofuels to Industrial Chemicals
Lanzatech is the largest gas fermentation company that produces ethanol jet fuel primarily from carbon monoxide. The company has positioned itself as a carbon recovery technology company, utilizing bacteria to convert exhaust gases into fuel.
The Illinois-based company was founded in 2005 and in 2022 announced plans to go public through a deal with AMCI Acquisition Corp that would unlock $275 million and increase its valuation to $2.2 billion. The company focuses on extracting carbon monoxide gas feedstock from steel mill exhaust, with operations at major steel mills in New Zealand, China. 2018 saw the first commercial use of jet fuel from steel emissions on a Virgin Atlantic flight.
Currently, only a few chemical products can be obtained efficiently by gas fermentation methods. Microorganisms capable of consuming gases are not particularly fast or efficient at absorbing carbon to make any chemicals other than biofuels. Other high-value chemicals, such as those used in personal care, are not yet commercially produced in significant quantities through gas fermentation. However, Lanzatech is now expanding beyond the aerospace industry. in February 2022, the company announced a pilot demonstration to produce waste carbon as acetone or isopropanol, the basic precursor for thousands of products in a number of industries, including fabrics, materials, and cosmetics. the company is now expanding beyond the aerospace industry, and in February 2022, it announced a pilot demonstration to produce waste carbon as acetone or isopropanol.
These new gaseous fermentation products were realized by reconnecting the microorganism C. autoethanogenum used in ethanol fuel production to produce acetone and isopropanol. The demonstration, published in Nature Biotechnology, concluded that Lanztech's gas gelatinization of acetone and isopropanol had negative life-cycle emissions, meaning that the entire fermentation process absorbed more carbon from the atmosphere than it released. The study also said that the method can be "easily adapted to a wide range of commodity chemicals."
Lanzatech's feedstock is carbon monoxide, not carbon dioxide. However, the company's new process for producing acetone and isopropyl alcohol may consume carbon dioxide, says CEO Jennifer Holmgren, and hydrogen is also being supplied for microbial consumption.
The company is currently expanding its partners in the consumer-facing chemicals industry. Its gas fermentation process is the technology behind Swiss sports brand Cloudprime shoes, which contain foam made from carbon emissions. The company's previous partnerships will also open doors to the consumer industrial chemicals market, such as its supply partnership with L'Oréal to supply ethanol-based polyethylene from 2020.
Other gas fermentation participants today
Lanzatech is the world's largest gas fermentation company, producing 90,000 tons per year, but smaller companies are now targeting the technology.
The University of Nottingham's Synthetic Biology Research Centre (SBRC), a center for gas fermentation research, has spawned two gas-fermented biomanufacturing startups, Deep Branch and PhaseBio.Founded by three former SBRC PhD students, Deep Branch produces sustainable animal feed from waste CO2 gas, raising over €8 million to build the FishKind single-cell protein pilot plant.
Unlike gas fermentation giant Lanzatech, the startup uses carbon dioxide instead of carbon monoxide, as well as hydrogen and oxygen. Microbes feed on these gases and electrolytes, which are dried and processed into single-cell proteins.
PhaseBio was founded in 2020 to convert industrial waste CO2 into chemicals and fuels. Like Deep Branch, their feedstock is carbon dioxide and hydrogen, rather than the carbon monoxide used by Lanzatech. Like Lanzatech, PhaseBio's approach is to set up fermentation technology at polluted industrial sites to collect waste and convert it into high-value commodities.
Commercialization challenges
There are a number of challenges before wider commercialization can be achieved. The biggest issue in the fouling approach is how to get carbon-eating microbes and yeast to consume and process the gas faster. Gene editing is now helping to improve the productivity of acetic acid-producing microbes.
As with all industrial fermentations, the practical challenges are enormous: manufacturers must consider the cost of raw materials versus the market value of the final biochemical product, and how to make a bad product by a single process.
Reactor design is important for viability. Optimizing mass transfer, i.e., the movement of the gas into the liquid, is one of the greatest limiting factors in increasing the productivity of gas fermentation. In order to reduce overall costs, the means of achieving mass transfer must be energy efficient.
