Researchers Develop an Enzyme That Eats Plastics

Tuesday, July 3, 2018 - 16:18

Scientists in Britain and the US say they have engineered an enzyme that eats plastic, a breakthrough that could help in the fight against pollution.

Researchers made the enzyme, which is able to digest polyethylene terephthalate, or PET. The team from the University of Portsmouth and the US Department of Energy's National Renewable Energy Laboratory hope to one day produce the enzyme on an industrial scale, Weird reports.

One single-use plastic bag takes at least 450 years to degrade. Give Miranda Wang three hours and she can reduce ten of them into liquid. Wang is the first to discover a chemical process that tackles the end-of-life of plastic.

Since the 1950s, 8.3 billion tons of plastic has been produced. It's now found in toys, car parts, in donor organs and in the oceans. Because of the centuries-long degradation period, most of it still exists: 6.3 billion tons of it as waste.

Recycling plastic today is a mechanical process. It is sorted by color, shredded, cleaned, and melted. But this is limited to only certain types of plastics: PET, used in water bottles, and HDPE, used in milk jugs. The five other types of commonly used plastics usually contain colorants and plasticizers that mean they cannot be recycled.

These are the plastics Wang has her sights on. “Our technology can turn these dirty films that have food or dirt or any kind of grime or any kind of contamination on it and we turn this material into a combination of four different kinds of chemicals, called organic acids,” says Wang.

In 2015, Yao and Wang, while they were still at college, founded BioCellection. The startup was based on their discovery of a bacteria that has evolved to eat plastic. But, it did not take long to realize that the bacteria would always prefer to eat whatever food contamination was on the plastic surface, and when it did eat the plastic, the speed at which it could digest it was far too slow.

Rather than using bacteria to breakdown the plastic, Wang uses a clear liquid catalyst. To prove that it works, she used plastic waste taken from a city waste plant in San Jose. “We shred this plastic, we put it into a flask and then we add our liquid catalyst,” she says.

“So instead of having one extremely long carbon chain, it forms many chemicals with shorter chains with four to eight carbons in size,” says Wang. “That is what is in the liquid at the end of the reaction.”

“The chemical identity of the content changes. That is why the plastic becomes a liquid in the end,” says Wang. “It is not a plastic liquid, it is a chemical liquid, because the plastic polymer has changed into chemicals.”

One of these chemicals is adipic acid, a precursor for materials like nylon and polyamines used in fashion, for electronic parts and in the automotive industry for car parts.

“Our vision is to transform a polyethylene, which right now does not have any downstream market value once it’s consumed and is used for one life cycle, and we turn it into a chemical that is of the same quality as what is immediately made from petroleum - adipic acid,” says Wang.

“This first helps us not allow film plastics from becoming pollution and second is that it actually displaces petroleum from being needed to be extracted to make new materials.”

Now, Biocellection is ready to scale. From the initial 10 plastic bags in a 500 milliliter flask breaking down in three hours, she is creating a continuous five liter system.

In 2019, they plan to build an even larger machine that will process five metric tons of plastic waste per day. This will be standardized, replicated and transported anywhere in the world where there is a lot of waste, where it can be plugged into a wall and left to run.

The next move is to expand beyond film plastics. “We can actually deal with any kind of polyethylene, even if it’s in a rigid form, as long as it’s shredded we can use it. But there are also opportunities in polypropylenes that we're interested in,” she says.

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