One of the reasons for the rapid changes in climatic conditions is an increase in the number of greenhouse gases in the atmosphere. Conventional methods used to decrease the level of carbon dioxide (CO2) are often inefficient and result in secondary pollution of the environment.
Greenhouse Gas Concept. Image Credit: Tatiana Grozetskaya/Shutterstock.com
Researchers have developed new technologies using microorganisms that can convert carbon dioxide into various valuable products. These technologies are highly beneficial as they not only reduce greenhouse gases but also produce value-added products.
Petrochemicals are extremely essential in our day to day lives. They constitute many objects such as electronics, paints, floors, clothing, cosmetics, furniture, packaging, cars, etc. Many of these products are not eco-friendly as they are non-biodegradable and non-recyclable. Another problem associated with the manufacturing of these products is the release of greenhouse gases that are detrimental to the environment.
Gas Fermentation
Gas fermentation is a microbial process that converts greenhouse gases into commodity products (chemicals and fuels). Bacteria can produce gases (syngas) via various microbial fermentation processes. These microbial processes can convert greenhouse gases such as carbon monoxide (CO) and CO2 to value-added chemicals or fuels using biocatalysts. This technology utilizes autotrophic, acetogenic bacteria as a biocatalyst. Examples of some acetogens are Clostridium ljungdahlii, Clostridium autoethanogenum, and Clostridium carboxidivorans.
These biocatalysts use the reductive acetyl-CoA pathway to fix CO2 and CO and subsequently produce biofuels such as ethanol, butanol, etc. They are also involved in the production of other bio-commodities, for example, acetate, butyrate, acetone, lactate, hexanoate, etc. In the syngas fermentation process, the use of thermophilic acetogenic biocatalyst is highly advantageous because of the following reasons:
- Reduces the risk of contamination
- Possesses superior metabolic and diffusion rates
- Reduces processing costs
Hence, syngas fermentation technology, if applied at an industrial-scale that emits a large amount of greenhouse gas on their manufacturing processes, has the potential to reduce environmental pollution and significantly impact climate change. In 2015, companies such as ArcelorMittal, LanzaTech, and Primetals Technologies, in collaboration with each other, have built a large-scale ethanol production facility in Ghent, Belgium. Scientists believe that the successful implementation of this technology at the large-scale industrial level would aid in promoting it globally.
Transformation of Greenhouse Gases to Usable Biodegradable Products
Scientists from the Wyss Institute for Biologically Inspired Engineering, Harvard University, have developed a new technology that uses engineered microbes for the production of synthetic polymers. The project is named Circe (Circular industries with cellular factories). Circe’s proprietary microbes utilize CO2 and hydrogen (H2) gases and subsequently produce polyhydroxyalkanoates (PHA), a class of biodegradable fatty acid polymers, via the process of gas fermentation. These polymers can be used to produce bioplastics, biodegradable polyesters, etc.
Circe envisions incorporation of their technology to an industrial process that emits greenhouse gases, and produce valuable polymers. This technology involves the installation of a carbon harvester at a CO2 or methane emission source. The carbon is combined with hydrogen and is supplied to microbes. Subsequently, the microbes are cultured and processed. Thereby, the polymers are purified and converted into a dried material so that they can be easily stored and shipped. These polymers are eco-friendly, non-toxic, and are biodegradable in nature.
Researchers at the project Circe are optimistic that their technology could be effectively utilized for the production of animal-free food products. The team at Circe is also optimistic that their technology could be implemented in the production of biodegradable products (smaller carbon footprints) related to single-use plastics, footwear, personal care products, packaging, electronics, and agriculture.
Transformation of Greenhouse Gases into Usable Chemical Compounds
Researchers at the University of South Florida are working on the development of technology that could convert greenhouse gases into usable chemical compounds. This technology would in turn help in reducing the use of petroleum in industries and thereby aid in lowering the carbon footprint.
Ramon Gonzalez, a Professor at the University of South Florida, and his research team have used the human enzyme, 2-hydroxyacyl-coenzyme A lyase (HACL), to convert specific one-carbon (C1) compound into more complex compounds. These complex compounds are commonly used in the development of various consumer and industrial products.
Gonzalez explained that in the human body HACL breaks down branched-chain fatty acids. Hence, this enzyme can degrade long carbon chains to smaller carbon chains. The focus of their research was just the opposite, i.e., conversion of smaller carbon compounds to larger carbon compounds. The team of researchers modified the DNA encoding the enzyme and inserted it into E. coli microorganisms.
When these E. coli are introduced to the C1 group, for example, formaldehyde, methanol, methane, carbon dioxide, etc., a metabolic bioconversion process takes place. This process converts the C1 compound to more complex compounds. Gonzalez stated that, currently, in the majority of oil production processes, gases like methane are burned-off. This method is not only wasteful but it also releases carbon dioxide and unburned methane into the atmosphere.
He said that their technology would be immensely beneficial to oil producers as it will have a lesser impact on the environment. In addition to environmental benefits, this technology is also involved in the production of valuable chemical compounds such as ethylene glycol and glycolic acid. These substances are used in the production of cosmetics, plastics, polymers, cleaning solutions, etc. Their research has the potential to decrease the number of greenhouse gases released into the atmosphere during crude oil production.
References and Further Readings
- Salehizadeh, H. et al. (2020). Recent advances in microbial CO2 fixation and conversion to value-added products. Chemical Engineering Journal. 390,124584. https://doi.org/10.1016/j.cej.2020.124584.
- Circe: Transforming Greenhouse Gases into Biodegradable Products. (2020). Wyss Institute at Harvard University.
- University of South Florida (USF Innovation). "Making microbes that transform greenhouse gases." ScienceDaily. ScienceDaily, 13 August 2019.
- Chou, A. et al. (2019). 2-Hydroxyacyl-CoA lyase catalyzes acyloin condensation for one-carbon bioconversion. Nature Chemical Biology. 15, 900-906. DOI: 10.1038/s41589-019-0328-0
- Bengelsdorf, R.F., and Durre, P. (2017). Gas fermentation for commodity chemicals and fuels. Microbial Biotechnology published by John Wiley & Sons Ltd and Society for Applied Microbiology, Microbial Biotechnology, 10, 1167–1170. https://sfamjournals.onlinelibrary.wiley.com/doi/pdf/10.1111/1751-7915.12763
Further Reading