Researchers hope the enzymes could create a truly circular system for the PET plastics that are still manufactured.
Of the 10 billion metric tons of plastic that humans have produced so far, only a small fraction has been recycled. Most of it sits in landfills or in the environment, where it could take centuries to degrade. But new plastic-eating enzymes could help begin to clean it up—and make recycling greener.
At the University of Texas at Austin, researchers created a new enzyme that can efficiently break down PET (a type of plastic commonly used in packaging and in materials like polyester) in days, even hours. Other scientists, including a team at the France-based startup Carbios, have worked with another version of the same enzyme; they recently built a pilot plant to biologically break down plastic to the molecular level so it can be remade into new products.
But the research from UT Austin, published in Nature, shows how it could happen at low temperatures, making the process more sustainable. “It means you have a much greener process, less energy intensive, and quicker,” says Hal Alper, a chemical engineering professor at UT Austin and one of the authors of the study. It also means that the enzyme could potentially be used for environmental remediation. “You can’t take plastic around the planet and heat it to hundreds of degrees Celsius at will,” he says. “But you can use something that works at ambient temperatures and pressure.”
The researchers started with an enzyme called PETase, which naturally evolved to make bacteria degrade PET plastic. Then they used machine learning to discover which mutations would make it possible for the process to happen faster and at relatively low temperatures. They tested the mutated enzyme on dozens of single-use plastic containers and several different polyester fabrics to demonstrate that it worked. In some cases, the enzymes fully degraded the plastic down to the monomer level—the basic building blocks of plastic—in less than a day.
In a recycling system, plastic that’s broken down in this way can be remade into new plastic that’s identical to the virgin material. “At traditional recycling plants, you’re essentially melting things down and then reforming [them],” Alper says. “Here, we’re actually breaking it back down to the original monomers, and then having the ability to rebuild it from there. So it has a huge advantage in that you don’t have the challenges that you have with normal recycling, where you lose some of the integrity of the plastic each time you go through a recycling process.” Unlike some other “advanced” recycling technology, it can happen with relatively little use of energy.
Solving the plastic waste problem will involve finding real alternatives to single-use plastic, like reusable packaging, so that plastic production dramatically drops. But the enzymes could potentially begin to tackle the huge volume of plastic that already exists and to theoretically create a truly circular system for the plastics that are still made. That will be a challenge, as it would involve building new infrastructure. (Because the first enzyme only works with one type of plastic, others will also have to be developed.) But the researchers hope to commercialize their enzyme technology, which has been patented. They’re in talks now with potential corporate partners. “I think this is a multi-industry problem,” Alper says.”And it’s gonna require a pretty large alliance and consortia to be able to solve this.”