Can enzymes really help solve the plastic crisis?

Buried in the dirt outside a plastic manufacturing plant, researcher Uwe Bornscheuer from Germany's University of Greifswald found his breakthrough.

Bacteria living there contained enzymes with the ability to break down polyurethane — the polymer used to create the foam in running shoes, mattresses and home insulation.

Around 16 million tons of fossil fuel-based polyurethane is discarded each year, and two-thirds of it ends up in landfill or incinerated for energy. The little that is recycled is largely ground up and turned into inferior products such as carpet underlay.

But Bornscheuer says his enzymes, known as urethanases, could unlock a new way to recycle the polymer. Using natural functions, they can quickly break it down to its constituent pieces, which can then be used to generate new polyurethane in a more environmentally friendly manner.

"We took pieces of polyurethane material, threw them in a beaker, threw in the enzyme. And it was completely degraded after two days," said Bornscheuer.

"I'm very confident that with the methods people use in my field, they can engineer the enzymes to do this within a few hours."

Recycling polymers such as polyurethane in this way would create a much higher quality end product than mechanical recycling, and could do it in a cleaner and more efficient way than the chemical recycling available today.

Tiny enzymes versus mountains of plastic waste

Cesar Ramirez-Sarmiento, associate professor at the Institute for Biological and Medical Engineering at Pontificia Universidad Catolica de Chile describes enzymes, which are a type of protein, as "the entities that actually take care of stitching things together or breaking them apart."

But with 460 million tons of oil and gas-based plastic manufactured in 2019 — a volume set to triple by 2060 — and as little as 9% of it recycled using more conventional means, plastic-tackling enzymes would need to work their way through mountains of the stuff. Around one billion tons of it annually by 2060.

There has been some success in using so-called PETase enyzmes to break down polyethylene terephthalate or PET, which is commonly used in bottles, clothes and packaging.

A French company called Carbios — partly funded by fast-moving consumer goods giants including Nestle and PepsiCo as well as clothing and beauty companies such as Patagonia, Puma and L'Oreal — has developed a demonstration plant in the central French region of Clermont-Ferrand that it says can break down two tons of PET in 10 hours using engineered enzymes.

The PET waste is turned into pellets, which PETase enyzmes reduce to monomers and impurities. The monomers can then be used to produce 100% recycled PET products, thereby allowing the limitless creation of essentially virgin PET. They can also be used to create entirely different products, such as pharmaceutical drugs. The impurities and the enzymes, however, are incinerated.

The firm is currently building a production site with a claimed capacity of 50,000 tons a year — equivalent to 2 billion plastic bottles. It is due to come online in 2025.

About 600 billion PET bottles are produced globally each year.

Research teams around the world are working on finding new enzymes to break down PET more efficiently and quickly and under various temperature and pressure conditions. Ramirez-Sarmiento has been searching as far afield as Antarctica to find new enzymes that can operate under cool temperatures.

What about other plastics?

Interest in enzyme degradation technology surged in recent years, when countries in Asia started refusing to accept plastic waste from other nations, according to Dongming Xie, Associate Professor in chemical engineering at the University of Massachusetts Lowell, in northeastern United States.

"I think this will be the direction of the future. We have to do it this way. Not just for PET plastics," Xie said.

A chance discovery in 2012 by hobby beekeeper and full-time microbiologist, Federica Bertocchini, shows promise for polyethylene (PE), which is used to create plastics bags, food wrap and containers, and accounts for about 30% of plastic generated.

Bertocchini had been extracting waxworm parasites from her beehives and collecting them in a plastic bag when she realized the larvae had created holes in the bag through chemical degradation. This sparked a years-long research focus into the enzymes that made it possible, said Bertocchini, a Principal Investigator at the Spanish National Research Council and Research Director at Plasticentropy.

The saliva of the waxworms contained two enzymes that can break polyethylene into its component parts. Unlike PET, however, these cannot be easily used to produce new polyethylene. Nor are they considered rubbish. Instead, early research shows the products could be upcycled for other industrial uses. The results of PET breakdown can be turned into the main flavor and aroma component of vanilla, and similar possibilities likely exist for polyethylene's constituent pieces, according to Bertocchini.

Research has shown that the waxworm enzymes may also be capable of degrading polystyrene, while research is ongoing with polypropylene.

Despite the promising results at experiment level, Bertocchini and her team have struggled to secure funding, meaning the lab is poised to close.

But it's not the only solution

Enzyme degradation technology will take a long time to reach maturity, and in the meantime Ramirez-Sarmiento says society needs to better manage the plastic coming onto the market, what it is made of and how it is disposed of. 

Mismanaging waste is one of the primary sources of plastic in the ocean.

Xie says plastics manufacturers have to play their part. "The plastic industry needs to work together with biologists," he said, stressing the need for them to consider the degradability of their plastics so they can be turned into new products after use.

Groups that campaign to end the production of plastic are unconvinced that enzyme technology can really make a difference. The only option is to stop producing plastic in the first place they say.

"Using enzymes is not likely to solve the plastics problem. It will not be able to handle the massive amount of plastic that floods the marketplace every year," said Judith Enck, President of Beyond Plastics, which is working to end plastic pollution. "The only real solution to the plastic pollution problem is to make less plastic."

Edited by: Tamsin Walker