Plastics and climate change an inextricably linked. Plastics are made from petroleum, and nearly every stage of their production creates greenhouse gas emissions. If plastic production and use grow as usual, by 2030 the emissions could reach 1.34 gigatons per year, equivalent to emissions from nearly 300 large coal-fired power plants, according to the Center for International Environmental Law.
In an effort to close the carbon cycle, chemical engineers in Korea have harnessed bacteria to efficiently turn carbon dioxide into a biodegradable plastic. This could be “an exceptional strategy for lowering CO2 emission and producing environmentally friendly bioplastics,” they write in Proceedings of the National Academy of Sciences.
Many innovators have been looking at producing useful chemicals, fuels and plastics from captured carbon dioxide emissions.The most extensive research efforts focus on using catalysts together with heat or electricity to turn carbon dioxide captured from industrial sources into plastics.
A newer route being pursued by researchers and some startups is to use bacteria that can capture carbon dioxide from the air and turn it into polyester. Over a decade ago, scientists found that a bacteria called Cupriavidus necator can ferment carbon sources and produce a degradable plastic called polyhydroxybutyrate (PHB). PHB is a biodegradable plastic that is considered, albeit questionably, an environmentally-friendly alternative to petroleum-derived plastics used to make food packaging, beverage bottles and disposable cutlery.
But the microbial fermentation process could only be done in small batches. That’s because it needed electricity to kick off, and the eventual buildup of toxic byproducts killed the microbes.
The team of chemical and biomolecular engineers at Korea Advanced Institute of Science and Technology have found a scalable solution. They came up with a biohybrid setup that combines electricity, catalysts and bacteria. They built a reactor with two chambers with a membrane separating them.
On one side, a tin catalyst spurs a chemical reaction that converts carbon dioxide gas into a formate chemical. The formate flows through the membrane to the other side, where C. necator ferments it, producing granules of the PHB plastic. The membrane keeps the bacteria away from the toxic byproducts.
In the paper, they report being able to operate the reactor continuously for 18 days by adding fresh bacterial cells and removing the polyester-containing cells. The system produced 11.5 mg of polyester per hour, about a hundred times more than reported numbers for similar systems, they report.
And while it still needs electricity, the team says that it could run on renewable electricity and should be easy and cost-effective to scale up.
Source: Jinkyu Lim et al, Biohybrid CO 2 electrolysis for the direct synthesis of polyesters from CO2, Proceedings of the National Academy of Sciences, 2023.