Enzyme-based plastics recycling more energy efficient, analysis suggests

The analysis - conducted by researchers in the Bottle Consortium, including representatives from the US Department of Energy’s (DOE’s) National Renewable Energy Laboratory (NREL) and the University of Portsmouth - identified that using enzymes could be a more sustainable approach for recycling polyethylene terephthalate (PET), a type of plastic commonly used to manufacture single-use beverage bottles, clothing and food packaging, all of which are increasingly relevant in addressing the environmental challenge of plastic pollution.

The new research addresses the challenges of plastic recyclability. While images of discarded bottles floating in oceans and other waterways provide a visual reminder of the problems posed by plastic waste, the lesser-seen issue remains of what to do with the PET used to manufacture in more obscure applications.

PET ranks among the most abundantly produced synthetic polymers in the world, with 82 million metric tonnes produced annually; roughly 54 per cent of PET is used in the manufacture of textiles for clothing and fibres for carpets.

According to the research team, the concept, if further developed and implemented at scale, could lead to new opportunities for PET recycling and create a mechanism for recycling textiles and other materials also made from PET that are traditionally not recycled today.

“From all the plastics that were produced since the 1950s, less than 10 per cent of it has ever been recycled,” said Avantika Singh, a chemical engineer at NREL and first author of a recent paper outlining the path toward enzyme-based recycling. “Most waste plastics end up in landfills.”

The Bottle ('Bio-Optimised Technologies to keep Thermoplastics out of Landfills and the Environment') Consortium aims to address the problem of plastic pollution with two innovative approaches: first, to develop energy-efficient, cost-effective and scalable recycling and upcycling technologies and, second, design modern plastics to be recyclable by design.

For the study, the researchers modelled a conceptual recycling facility that would take in a fraction of the three million metric tonnes of PET consumed annually in the US. The enzymatic recycling process breaks down PET into its two building blocks, terephthalic acid (TPA) and ethylene glycol.

The researchers found that, compared to conventional fossil-based production routes, the enzymatic recycling process can reduce total supply chain energy use by 69-83 per cent and greenhouse gas emissions by 17-43 per cent per kilogram of TPA. An economy-wide comparison of virgin TPA and recycled TPA in the US also shows that the environmental and socioeconomic effects of the two processes are not distributed equally across their supply chain.

According to the research team, the proposed recycling process can reduce environmental impacts by up to 95 per cent, while generating up to 45 per cent more socioeconomic benefits, including local jobs at the material recovery facilities.

The study also predicts that enzymatic PET recycling can achieve cost parity with the production of virgin PET. This highlights the potential for this enzyme technology to decarbonise PET manufacturing, besides enabling the recycling of waste PET-rich feedstocks, such as clothing and carpets.

“That’s one of the biggest opportunities,” Singh said. “If we can capture that space – textiles, carpet fibres and other PET waste plastics that are not currently recycled – that could be a true game-changer.”