Global problem: Enzymes to 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.

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.

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.