Enzymatic PET degradation for a circular economy: Researchers reframe experimental standards

04 Dec 2023 --- A team of researchers has demonstrated how changes in experimental standards and methodologies can help improve the rate at which plastic degrading enzymes can be effectively developed for industrial waste management. The findings are demonstrated by the creation of four newly discovered enzymes.

The research was conducted by Gert Weber of Helmholtz-Zentrum Berlin, Uwe Bornscheuer of the University of Greifswald and Alain Marty, Carbios’ chief scientific officer.

Many enzymes appear to work effectively in laboratory conditions but lose their impact quickly when applied to real-world scenarios.

When a PET-degrading enzyme is discovered, for example, the researchers making the discovery usually fall silent after announcing their findings because their discoveries do not work in large-scale bioreactors.

“In recent years, enzymatic recycling of the widely used polyester PET has become a complementary solution to current thermomechanical recycling for colored, opaque and mixed PET,” state the researchers.

“A large set of promising hydrolases that depolymerize PET have been found and enhanced by worldwide initiatives using various protein engineering methods. Despite the achievements made in these works, it remains difficult to compare enzymes’ performance and their applicability to large-scale reactions due to a lack of homogeneity between the experimental protocols used.”

Enzymatic recycling of PET at scale is a challenge researchers are struggling to overcome.Together with the biotech company Carbios, Uwe Bornscheuer and Gert Weber have shown how new enzymes for PET degradation can be better compared with each other, the authors say. The research is published in the journal ACS Catalysis.

New PET protocols
To create more homogenous experimental methods, the team developed a standardized PET hydrolysis protocol that defines reaction conditions relevant to hydrolysis on a larger scale.

In particular, two PET materials were used. The first is a defined PET film, and secondly PET granulate from waste bottles, as used by Carbios on a technical scale. The study authors used these materials to test four recently discovered PET-decomposing enzymes: LCC-ICCG, FAST-PETase, HotPETase and PES-H1L92F/Q94Y.

When experimenting under this protocol, the scientists found that two of these enzymes, FAST-PETase and HotPETase, were less suitable for large-scale use, mainly due to their relatively low depolymerization rates. PES-H1L92F/Q94Y performed better.

The fourth candidate, LCC-ICCG, outperformed the other enzymes: LCC-ICCG converts 98% of PET into the monomeric products terephthalic acid (TPA) and ethylene glycol (EG) in 24 hours.

Finding feasibility in PET hydrolysis
The authors say the study will contribute to finding a consensus on the methods used and key parameters to consider when performing a large-scale PET depolymerization.

“Such a consensus is necessary for deploying the first generation of enzymatic PET recycling processes at an industrial scale,” they state.

“We also believe that this field will further benefit from new technologies to emerge as well as new superior enzymes being able, for instance, to perform efficient degradation of semicrystalline PET to minimize the PET pretreatment steps as underlined in a previous study.”

“Ultimately, new acid-tolerant PET hydrolases able to perform efficient PET depolymerization with no (or a minimal) need of soda for pH regulation would also be of great interest to further strengthen the concept of enzymatic PET hydrolysis in the frame of a circular economy.”

“We anticipate our findings to advance enzymatic PET hydrolysis toward a coherent assessment of the enzymes and materialize feasibility at larger reaction scales.”

By Louis Gore-Langton

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