University of Portsmouth researchers have contributed to a groundbreaking study showing enzyme-based plastic recycling could become commercially viable, potentially revolutionising how the world tackles plastic waste management and environmental sustainability.
An international team of scientists has developed a revolutionary recycling method that could drastically cut both the financial and environmental costs of processing PET plastic – the material most commonly found in bottles and food packaging – offering hope for transforming global plastic waste management.
The innovative approach, spearheaded by the US Department of Energy’s National Renewable Energy Laboratory (NREL) and featuring Professor Andrew Pickford, Director of the Centre for Enzyme Innovation (CEI) at the University of Portsmouth, presents a series of breakthroughs that pave the way for future enzymatic PET recycling to become not only environmentally friendly but also more economical than manufacturing new plastic from fossil fuels.
Published findings in Nature Chemical Engineering demonstrate that this new method reduces greenhouse gas emissions by almost 50 per cent whilst cutting operational costs by 74 per cent compared to existing techniques. The most notable advancement involves substituting sodium hydroxide with ammonium hydroxide – a seemingly minor chemical change that delivered significant improvements.
“Sometimes, the key to a global challenge lies in rethinking a single chemical,” said Professor Pickford. “By selecting 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 use of ammonium hydroxide not only maintained the necessary pH levels for enzymatic PET breakdown but enabled in-process regeneration of the base through thermolysis of the breakdown product, virtually eliminating the need for fresh acid and base chemicals. Research showed these process modifications reduced expensive acid and base additions by more than 99 per cent, cut annual operating costs by 74 per cent, and decreased energy consumption by 65 per cent.
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This new method tackles longstanding obstacles in enzymatic recycling. Whilst mechanical recycling proves energy efficient, much of the PET waste stream – including coloured plastics, thermoforms, and textile fibres – remains unsuitable for this approach. Enzymatic recycling provides a solution for breaking PET down into its fundamental chemical components, though until now it has faced prohibitive costs and environmental drawbacks.
Professor John McGeehan, who recently transferred to the NREL team from the University of Portsmouth, commented: “I am delighted to be part of a team that is dedicated to translate fundamental science towards real-world application and look forward to working closely between NREL and our industry partners to accelerate the design and construction of the first US enzymatic plastic recycling plants.”
Dr Gregg Beckham, co-lead researcher from NREL, added: “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 realise an economically viable and scalable process.”
From a technical perspective, employing ammonium hydroxide enables the production of diammonium terephthalate, which can subsequently be broken down through thermolysis to regenerate ammonia and produce pure terephthalic acid – one of PET’s two essential building blocks. This allows the base to be reused indefinitely, dramatically reducing waste and raw material requirements.
Beyond the ammonia-based innovation, researchers optimised plastic pre-treatment through extrusion and quenching, achieving complete depolymerisation within 50 hours. The process also enhanced recovery of ethylene glycol, another core PET component, by increasing its concentration during fed-batch processing.
The outcome was a closed-loop PET recycling system with a minimum selling price of $1.51/kg, undercutting the $1.87/kg cost of virgin PET production.
Professor Pickford noted: “PET is one of the most widely used plastics globally, and its current low recycling rates represent a major environmental concern. This marks the first time enzymatic recycling of PET has appeared not only environmentally preferable but commercially viable. It’s the sort of progress we need if we’re serious about ending plastic pollution.”
Though the process awaits industrial-scale implementation, researchers remain optimistic that this study brings positive change significantly closer.
The research collaboration comprises scientists from the National Renewable Energy Laboratory (NREL), the University of Massachusetts Lowell, and the University of Portsmouth.
These organisations previously collaborated on the biological engineering of enhanced PETase enzymes capable of breaking down polyethylene terephthalate (PET). With its low manufacturing cost and excellent material properties, PET sees extensive use in single-use packaging, soft drink bottles, and textiles.
