For similar, related concepts, see the Mitigating Environmental Pollution theme in this roadmap.
While greenhouse gas (GHG) emissions from the production of chemicals, including plastics, is not as significant as some other sectors and industries, it is still hugely impactful on the climate. Chemical manufacturing, excluding ammonia production, directly emits about half a gigatonne of CO2 globally each year, which is less than 2% of the global GHG emissions, but is the single largest industrial consumer of oil and gas.1International Energy Agency. (2021). Chemicals – Analysis. IEA. View Publication. One area of research and development that has progressed rapidly, especially within the last 5-10 years, is bioprocesses for chemical production. Microbial engineering has the capacity to enable the production of a wide array of diverse chemicals and compounds, reducing the amount of resources and toxins that might otherwise be consumed or produced, respectively. Today, most molecules produced commercially with microbes are high-value specialty chemicals such as flavors and fragrances, cosmetic additives and pharmaceuticals with only a handful of examples of commodity chemicals including ethanol, 1,3-propanediol, 1,4-butanediol, isobutanol, farnesene, lactic acid and succinic.2Jullesson, D., David, F., Pfleger, B., & Nielsen, J. (2015). Impact of synthetic biology and metabolic engineering on industrial production of fine chemicals. Biotechnology Advances, 33(7), 1395–1402. View Publication. If the thousands of chemicals derived from petroleum and natural gas could be produced instead with microbes, the annual savings in GHG emissions would be substantial. Most products manufactured through engineering biology approaches today generally have lower emissions than conventional petrochemical counterparts3Adom, F., Dunn, J. B., Han, J., & Sather, N. (2014). Life-Cycle Fossil Energy Consumption and Greenhouse Gas Emissions of Bioderived Chemicals and Their Conventional Counterparts. Environmental Science & Technology, 48(24), 14624–14631. View Publication. but are not been fully carbon neutral, in part because they rely on yeast or E. coli and yeast that emit substantial amounts of CO2 waste in order to generate highly reduced products from oxidized starting materials, namely, sugars. They must be engineered to be circular or, for example, combined into distributed metabolism systems with autotrophic bacteria.4Scown, C. D., & Keasling, J. D. (2022). Sustainable manufacturing with synthetic biology. Nature Biotechnology, 40(3), 304–307. View Publication.
Once the feedstock, whether it is sugars or a gaseous input, is converted to a product, the ultimate use and disposal (or recycling) of that product is the key to whether it will sequester carbon or simply release CO2 back to the atmosphere. Certain bioproducts do have greater potential to lock carbon away in a stable form in particular polymer materials. Additionally, the persistence of materials such as plastics in the environment, they result in significant contribution to pollution, environmental damage, and worsening climate change. Millions of metric tons of plastics are created each year and that production is expected to continue, if not grow. However, some sources suggest that up to 90% of plastics could come from plant-derived alternatives.5Hottle, T., Gorman, M.R., & Frischmann, C. (2020). Bioplastics @ProjectDrawdown #ClimateSolutions. Project Drawdown. View Publication. Biobased alternatives, and chemicals and “plastic” materials produced through bioprocesses (biobased methods), can significantly reduce this impact.
Not only would this reduce the amount of petrochemicals that go into plastic production, but would enable greater flexibility for biodegradation, including into other value-added compounds (see Washington, 20216Washington. (2021). Genetically engineered microbes convert waste plastic into vanillin. Chemistry World. View Publication. in example). One of the biggest current technical challenges to bioplastics is attaining the strength and other physical and mechanical properties of plastics already on the market. While processes exist to create polylactic acid (PLA) from corn and sugarcane, and polyhydroxyalkanoate (PHA) from algae, these polymers and subsequent compounds aren’t sufficiently tunable, or capable of being produced at economically-advantageous scales and prices.7Robbins. (2020). Why Bioplastics Will Not Solve the World’s Plastics Problem. Yale E360. View Publication. These bioplastic materials also need to have controlled biodegradation pathways engineered and adapted to the appropriate conditions and environments.
One area of research and development that has progressed rapidly, especially within the last 5-10 years, is bioprocesses for commodity chemical production. Microbial engineering has the capacity to enable the production of a wide array of diverse, high-value chemicals and compounds,8Jullesson, D., David, F., Pfleger, B., & Nielsen, J. (2015). Impact of synthetic biology and metabolic engineering on industrial production of fine chemicals. Biotechnology Advances, 33(7), 1395–1402. View Publication. reducing the amount of resources and toxins that might otherwise be consumed or produced, respectively. However, these processes still produce significant amounts of CO2, so to be efficient and sustainable, they must be engineered to be circular or engineered for distributed metabolism.
In addition to removing pollutants from the environment, engineering biology could go one step further and upcycle pollutants by converting them into useful products.9Cornwall. (2021). Could plastic-eating microbes take a bite out of the recycling problem? Science. View Publication. For example, by using bacteria to recycle electronic waste, convert plastic waste into other, value-added compounds, sustainably remediate and extract heavy metals from waste waters, and more.10Kwok, R. (2019). How bacteria could help recycle electronic waste. Proceedings of the National Academy of Sciences, 116(3), 711–713. View Publication., 11Washington. (2021). Genetically engineered microbes convert waste plastic into vanillin. Chemistry World. View Publication., 12Sun, G. L., Reynolds, E. E., & Belcher, A. M. (2020). Using yeast to sustainably remediate and extract heavy metals from waste waters. Nature Sustainability, 3(4), 303–311. View Publication., 13Yang, G., Tan, H., Li, S., Zhang, M., Che, J., Li, K., Chen, W., & Yin, H. (2020). Application of engineered yeast strain fermentation for oligogalacturonides production from pectin-rich waste biomass. Bioresource Technology, 300, 122645. View Publication. Key challenges to this are complex and compound metabolic engineering, such as engineering microbiomes capable of distributed metabolism, and attaining circular, closed-loop bioprocessing.