Process strategies to improve biocatalytic depolymerization of post-consumer PET packages in bioreactors, and investigation on consumables cost reduction

Massive plastics production has raised concerns about low recycling rates and disposal of these materials in nature, causing environmental and economic impacts. Poly(ethylene terephthalate) (PET) is one of main polymers used for manufacture of plastic packaging (e.g. bottles, trays). Enzymatic recycling of PET has been a route of increasing study aiming at to recover its monomers (terephthalic acid and ethylene glycol), resulting in a circular production chain. In this study, investigation of pH control and fractionation of enzyme feeding were explored in post-consumed PET (PC-PET) hydrolysis reactions catalyzed by Humicola insolens cutinase (HiC) in stirred reactors. It was found that the unbuffered reaction provided of pH control by 0.5 M NaOH addition showed 2.39-fold improvement in the released monomers (to a total of 26.3 mM), comparatively to the Tris-HCl-buffered reaction. In addition, it was observed a possibility of reducing the enzyme loading used in the process by half, leading to an increase of 2.41-fold in the specific terephthalic acid concentration released per protein amount, whilst maintaining a high products concentration (97 mM). A simplified cost analysis of reaction consumables was performed, and the data reported here demonstrates that these alternative process strategies contribute to costs reduction on the enzymatic depolymerization reactions of PET.

Automated summary

The study explores the enzymatic hydrolysis of post-consumed PET using Humicola insolens cutinase, focusing on pH control and enzyme feeding. Results show that unbuffered reactions with pH control by NaOH addition significantly improve monomer release, and reducing enzyme loading by half leads to cost reduction while maintaining high product concentration.