Scientists have developed a new enzyme variant that can completely break down waste plastic in under 24 hours, raising hopes that biological processes could provide a route to addressing perhaps part of the world’s mounting plastic crisis.
Researchers at the University of Texas at Austin announced Thursday that they had used artificial intelligence to successfully engineer a type of enzyme, called a hydrolase, that can break down PET plastic into its component molecules. These materials can then be reformed into new products.
“The possibilities are endless across industries to leverage this leading-edge recycling process,” said Hal Alper, one of the lead researchers and a professor in the McKetta Department of Chemical Engineering at UT Austin. “Beyond the obvious waste management industry, this also provides corporations from every sector the opportunity to take a lead in recycling their products. Through these more sustainable enzyme approaches, we can begin to envision a true circular plastics economy.”
PET—full name polyethylene terephthalate—is one of the most common plastics and accounts for some 12% of the manmade solid waste in the world, being used to make products such as soda bottles and disposal food trays.
The researchers demonstrated a whole circular recycling process, using the enzyme to completely break down plastic samples into materials that they then used to generate entirely new pieces of PET. Notably, the process worked just as well with mixed-colour PET as it did with clear products.
Previous attempts to use enzymes to break down PET have been constrained by a range of factors, from the enzymes’ vulnerability to temperature and pH ranges, to their sluggish reaction rates. But this “robust” enzyme, the researchers believe, will be able to handle temperature variations in non-laboratory conditions.
“When considering environmental cleanup applications, you need an enzyme that can work in the environment at ambient temperature,” Alper said. “This requirement is where our tech has a huge advantage in the future.”
In sufficient quantities, the enzyme could be use to clean up plastic-strewn landfills and waste plants, or simply sites that have been polluted by plastics.
With 400 million tons of plastic being disposed of every year, new solutions to the plastic waste crisis are badly needed. Less than 10% of the world’s plastic trash is recycled; the rest breaks down in the environment, polluting the water, the food chain and even the air. As a result, plastic has now been found everywhere on Earth, from the atmosphere to human blood.
The health consequences of this for humans are, for the time being, largely unknown, but they are unlikely to be beneficial. Research so far has shown that microplastics in humans can cause cell damage.
In March, 175 members of the United Nations agreed for the first time to forge an international plastics treaty to tackle plastic pollution. Crucially, such a treaty will be expected to address the upstream problem of the oversupply of plastics, which is being driven principally by the oil and gas industry.
The paper “Machine learning-aided engineering of hydrolases for PET depolymerization” can be viewed at Nature. A subscription is required to view the full article.