A team of chemical engineers in Korea has developed a new system that could help tackle two global problems: plastic waste and rising levels of carbon dioxide. The system uses a bacterium called Cupriavidus necator to transform carbon dioxide from the air into a bioplastic. While plastic-munching bacteria have gained attention for breaking down plastic waste, this new approach focuses on finding new ways to make plastics from sources other than crude oil and its derivatives. The rising levels of carbon dioxide in the Earth’s atmosphere could be an untapped resource for making plastics or other carbon-based products, such as jet fuel or concrete. However, converting CO2 gas into other useful carbon-containing compounds is a challenging and inefficient task.
The System
The two-part system created by the team of chemical engineers at the Korea Advanced Institute of Science and Technology (KAIST) involves an electrolyzer and a fermentation tank. The electrolyzer converts gaseous CO2 into formate, which is then fed into the fermentation tank. C. necator then synthesizes carbon compounds such as poly-3-hydroxybutyrate (PHB) from the formate feedstock. PHB is a type of biodegradable and compostable polyester that can be extracted from harvested cells. The same solution circulates between the electrolysis reaction and the fermentation tank, with a membrane separating the two chambers so that the bacteria are isolated from the by-products of the electrolysis reaction.
The Results
Lab experiments showed that C. necator cells in the hybrid system could synthesize so much PHB that after 120 hours or 5 days of operation, the polyester product represented up to 83 percent of the bacteria’s dry cell weight. The researchers claim that their set-up is 20 times more productive than similar systems tested previously. The team also reports that their system can operate continuously as long as the bacterial cells are replenished each day and the plastic product is removed to keep the reactions going. Continuous production would be key to making the system work at industrial scales.
The Future
If the system is powered by renewable energy, then it could be a fossil-fuel-free way of generating bioplastics that simultaneously makes use of CO2. Hyunjoo Lee and Sang Yup Lee, two biomolecular engineers at KAIST who led the study, are optimistic that their approach is scalable and could transform the way plastics get made. The researchers say that their integrated system is an improvement on previous batch reactors or other set-ups that can only operate one phase of the reaction at a time and require additional separation and purification steps. While the researchers have only tested the system for 18 days and produced 1.45 grams worth of polyester, they believe their approach is worth pursuing as an option to help achieve carbon neutrality in the future. Meanwhile, other biochemical engineers are trying to enhance C. necator’s natural ability to produce PHB from CO2 with a few genetic tweaks because the amount of polymer produced by C. necator is still too low for commercialization.
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