Plastic-eating enzyme tackles landfill waste
An enzyme variant created by engineers and scientists at the University of Texas (UT) in Austin can break down plastics that typically take centuries to degrade in just a matter of hours to days.
The enzyme, details of which have been published in Nature, could help solve one of the world’s most pressing environmental problems: what to do with the billions of tons of plastic waste piling up in landfills and polluting the land and water. It has the potential to significantly boost recycling on a large scale and allow major industries to reduce their environmental impact by recovering and reusing plastics at the molecular level.
However, it’s not all plastic. The focus, for now, is on polyethylene terephthalate (PET), a significant polymer found in most consumer packaging, including biscuit containers, water and soft drink bottles, fruit and salad packaging, and certain fibres and textiles — about 12% of all global plastic waste.
The enzyme can break the plastic down into smaller parts (depolymerisation) and then chemically put it back together (repolymerisation). In some cases, these plastics can be fully broken down to monomers — which can then be bonded to form polymers — in as little as 24 hours.
Researchers at the Cockrell School of Engineering and College of Natural Sciences used machine learning to generate novel mutations to a natural enzyme called PETase that allows bacteria to degrade PET. The model predicts which mutations in these enzymes would quickly depolymerise post-consumer waste plastic at low temperatures.
“This work really demonstrates the power of bringing together different disciplines, from synthetic biology to chemical engineering to artificial intelligence,” says Andrew Ellington, professor in the Centre for Systems and Synthetic Biology, whose team led the development of the machine learning model.
Globally, less than 10% of all plastic has been recycled. The most common method for disposing of plastic — besides dumping it in landfill — is to burn it, which is costly, energy-intensive and highly-pollutive. There are other industrial processes — glycolysis, pyrolysis, and/or methanolysis — but they use a lot of energy.
Biological solutions take way less energy. And while research on enzymes for plastic recycling has advanced in the past 15 years, until now, no one has been able to figure out how to make enzymes that could operate efficiently at low temperatures to make them both portable and affordable at large industrial scale. This enzyme can do the work at less than 50°C.
Up next, the team plans to work on scaling up enzyme production to prepare for industrial and environmental use. The researchers have filed a patent application and are eyeing several different uses. Cleaning up landfills and high waste-producing industries are the most obvious. But another key potential is environmental remediation and the team is looking at a number of ways to get the enzymes out into the field to cleanup polluted sites.
“When considering environmental cleanup applications, you need an enzyme that can work in the environment at ambient temperature. This is where our tech has a huge advantage in the future,” says Professor Hal Alper from the McKetta Department of Chemical Engineering at UT Austin.
FULL DISCLOSURE: This work was funded by ExxonMobil’s research and engineering division as part of an ongoing research agreement with UT Austin.