In 2016, a Kyoto Institute of Technology microbiologist, Kohei Oda, inspected the waste at a plastic bottle recycling site in Japan. When inspecting polyethylene terephthalate (PET) bottles, he stumbled across a new strain of bacterium, Ideonella Sakaiensis (ISK). Upon investigation, Oda and his researchers found that when the bacterium breaks down, it forms two enzymes: METase and PETase. Combined, the enzymes unfold - or reverse engineer - the PET manufacturing process. In essence, the bacterium is able to depolymerise PET into its constituent monomer components.

Reminiscent of when Alexander Flemming returned from holidays to find cultures in his lab containing a ‘bacteria-killing fungus’ - the building block of penicillin – Oda’s findings catalysed a cascading ripple of innovation.

Oda’s team discovered the first bacterium that could break pure PET products – something other bio-remedial techniques had only managed to do with blends of bioplastic. However, ISK’s scalability is somewhat limited; to break down PET, ISK takes over 6 weeks, requires specific temperature conditions, and needs a lot of energy to do the job. To that effect, numerous scientists have looked to improve the process and scale up enzymatic recycling to make it commercial. For example, Portsmouth University biologist, John McGeehan, has modified PETase by linking it with other enzymes, generating “super-enzymes” that can eat about six times faster than the incumbents.

Building on this technique, French biotechnology firm, Carbios, has found a means of breaking down the monomers using genetically-modified microorganisms. Their solution, proven in their pilot plant in Clermont-Ferrand, can operate faster, use less energy, and crucially, breaks down polymer chains so that they can be recirculated back into plastic production.

Are these solutions really necessary given that we already have an established means of recycling PET? Believe it or not, your conventional PET bottle can only be recycled three to five times until the monomers’ quality is deemed too low to go back into plastic production. In contrast, Carbios’ solution is able to recirculate monomers back into plastic between thirty and fifty times – a considerably more circular solution.

While enzymatic solutions only deal with PET – which constitutes 20% of net plastic waste - they are a step in the right direction in a world where only 10% of plastics are recycled. As the pressure increases from plastics regulations, such as the 2022 Plastic Tax and Extended Producer Responsibility, as well as public and corporate demands for increased recycling rates, the price of recycled granulates is rapidly increasing. The key challenge now is scaling up enzymatic recycling technologies to a stage where they can compete with virgin and conventional recycled plastics. As soon as they can, there’s a strong chance that this slightly more leftfield solution will play a major role in the plastics circular economy stage.