PET — polyethylene terephthalate — is the plastic in most water bottles, food containers, and synthetic textiles. It is also one of the most persistently produced materials on earth: roughly 70 million tons manufactured annually, much of it ending up in landfill or the ocean, where it will remain for centuries. Chemical recycling, the process of breaking PET back down into its constituent monomers for re-use, has long been held back by one problem: it requires high temperatures and harsh chemicals, making it expensive and energy-intensive.
An engineered enzyme, reported in a study published this week, breaks PET down into its monomers at room temperature, in water, in under twelve hours. The starting material was a bacterium discovered in a plastic-degrading ecosystem near a recycling facility in Japan. The enzyme it produces, originally sluggish and unstable, has been optimized through directed evolution into something that performs thousands of times faster — and that can now be produced at industrial scale.
How it works
The enzyme, designated PETase-Ultra in the paper, attacks the ester bonds that hold PET’s polymer chains together. Those bonds are the source of PET’s durability; they are also, it turns out, accessible to a protein that has been evolved specifically to break them. The monomers produced — terephthalic acid and ethylene glycol — are the same ones used to manufacture virgin PET, meaning they can be fed directly back into plastic production without any intermediate processing.
The result is a closed loop: plastic made from monomers, broken back down to monomers, made into plastic again, indefinitely.
What stands between the lab and the recycling plant
Scale is the first problem. The enzyme works beautifully on pure, clean PET flakes. Real-world plastic waste is contaminated with dyes, adhesives, food residue, and other polymers. Trials on mixed-stream waste are ongoing, but the degradation rate drops significantly when the substrate is impure.
Cost is the second. Enzyme production is currently more expensive per ton of plastic than mechanical recycling. The team estimates that at current enzyme yields, chemical recycling via PETase-Ultra costs roughly twice as much as landfill. That gap narrows as production scales, but it has to narrow enough to compete.
The third problem is systemic: recycling rates for PET, even in countries with established infrastructure, hover around 30 percent. A better recycling technology does not solve the problem of plastic that never makes it to a recycling stream. That is a policy problem, and enzymes don’t vote.
