Enzyme breakthrough cuts plastic recycling energy use by 65%

Plastic’s toughest problem may have just met its smartest solution.

A team of scientists from the National Renewable Energy Laboratory (NREL), the University of Massachusetts Lowell, and the University of Portsmouth in England has unveiled a game-changing enzymatic recycling process of breaking down PET, the world’s most widely used plastic.

For the first time, breaking down used PET into its building blocks is not only cleaner than making new plastic from oil, it’s also cheaper and has a lower carbon footprint.

A smarter chemical switch

Led by the U.S. Department of Energy’s National Renewable Energy Laboratory (NREL) and the University of Portsmouth’s Centre for Enzyme Innovation, the research introduces a subtle but pivotal chemical switch by replacing sodium hydroxide with ammonium hydroxide.

That single tweak has unlocked a self-sustaining recycling loop that slashes chemical use by 99 percent, reduces energy consumption by 65 percent, and cuts operating costs by nearly three-quarters.

“Sometimes, the key to a global challenge lies in rethinking a single chemical,” said Professor Andrew Pickford, director at Portsmouth’s enzyme centre and a senior author of the study.

“By choosing a different base, one that could be recycled within the process, we managed to close a loop and significantly improve both the sustainability and the economics of the system.”

The new process tackles long-standing hurdles in enzymatic recycling. While mechanical recycling is energy-efficient, it can’t handle much of the PET waste stream, such as coloured plastics, thermoforms, and textile fibres.

Enzymatic recycling can break PET down to its core chemical components, but until now, high costs and environmental drawbacks have held it back.

The closed-loop process brings the cost of recycled PET down to $1.51 per kilo, cheaper than virgin plastic, which currently sells for $1.87.

Ammonium hydroxide not only maintained the optimal pH for enzymatic PET breakdown but also regenerated itself during the process through thermolysis of a byproduct. This nearly eliminated the need for fresh acid and base chemicals.

“Despite the advantages of enzymatic recycling for complex plastic waste streams, the field has encountered multiple challenges for realistic implementation. Here we have taken a multidisciplinary approach that incorporates multiple innovations to realize an economically viable and scalable process,” Dr Gregg Beckham, co-lead of this study.

Cracking closed-loop code

In parallel, the researchers enhanced plastic pre-treatment through optimized extrusion and quenching, achieving complete depolymerization within 50 hours.

The process also improved ethylene glycol recovery by increasing its concentration during fed-batch processing, boosting efficiency for this second key PET component.

“PET is one of the most widely used plastics in the world, and its current low recycling rates are a major environmental concern,” Pickford said.

“This is the first-time enzymatic recycling of PET has looked not only environmentally preferable, but commercially viable. It’s the sort of progress we need if we’re serious about ending plastic pollution.”

While the process has yet to be implemented at an industrial scale, the researchers remain optimistic that it could pave the way for greener plastic recycling. This study brings that vision one step closer to reality.