Plastic bottles, trays, packaging: lightweight PET plastic packaging becomes problematic if it is not recycled. Scientists at the University of Leipzig have just discovered a highly efficient enzyme that degrades PET in record time. The enzyme PHL7, which the researchers found in a compost heap in Leipzig, could make the biological recycling of PET possible much faster than previously thought. The results have just been published in the scientific journal ChemSusChem and selected as the cover subject.
Enzymes are used in nature by bacteria to break down parts of plants. It has been known for some time that certain enzymes, called polyester cleavage hydrolases, can also degrade PET. For example, the LCC enzyme, discovered in Japan in 2012, is considered a particularly effective “plastic eater”. The team led by Dr. Christian Sonnendecker, an early-career researcher from the University of Leipzig, is researching previously unknown examples of these biological aids in the EU-funded MIPLACE and ENZYCLE projects. They found what they were looking for at the Südfriedhof, a cemetery in Leipzig: in a sample from a compost heap, the researchers came across the imprint of an enzyme that breaks down PET at record speed in the laboratory.
Researchers at the Institute of Analytical Chemistry have found and studied seven different enzymes. The seventh candidate, called PHL7, performed well above average in the lab. In the experiments, the researchers added PET to containers with an aqueous solution containing either PHL7 or LCC, the former leader in PET breakdown. Then they measured the amount of plastic degraded over a given period of time and compared the values to each other.
Result: in 16 hours, PHL7 caused the decomposition of PET to 90%; at the same time, LCC managed a degradation of only 45%. “Our enzyme is therefore twice as active as the gold standard among polyester-cleaving hydrolases,” says Sonnendecker. For example, PHL7 broke a plastic tray – the kind used to sell grapes in supermarkets – in less than 24 hours. The researchers found that a single building block of the enzyme is responsible for this above-average activity. At the site where other previously known polyester cleavage hydrolases contain a phenylalanine residue, PHL7 carries a leucine.
Biological recycling of PET has some advantages over conventional recycling methods, which mainly rely on thermal processes where plastic waste is melted at high temperatures. These processes are very energy intensive and the quality of the plastic decreases with each recycling cycle. Enzymes, on the other hand, only require an aqueous environment and a temperature of 65 to 70 degrees Celsius for their work. Another benefit is the fact that they break down PET into its components terephthalic acid and ethylene glycol, which can then be reused to produce new PET, resulting in a closed cycle. So far, however, the biological recycling of PET has only been tested by a pilot plant in France.
“The enzyme discovered in Leipzig can make an important contribution to the establishment of alternative, energy-efficient plastic recycling processes,” says Professor Wolfgang Zimmermann, who has played a key role in setting up research on enzyme-based technologies at the University of Leipzig. “Due to the enormous problems caused by the global burden of plastic waste on the environment, it is becoming increasingly important to find environmentally friendly methods to reuse plastic in a sustainable circular economy. The biocatalyst now developed at Leipzig has proven to be very effective in the rapid breakdown of used PET food packaging and is suitable for use in an environmentally friendly recycling process in which new plastics can be produced from the decomposition products.”
The Leipzig researchers hope that the newly discovered enzyme PHL7 can advance biological recycling in practice and are looking for industrial partners for this purpose. They are confident that the higher speed will significantly reduce recycling costs. In the next two to three years, they aim to create a prototype that will more accurately quantify the economic benefits of their rapid biological recycling process.
Scientists from Professor Jörg Matysik’s team at the Institute for Analytical Chemistry also want to elucidate the structure and function of enzymes using NMR spectroscopy. They’re also working on a new pre-processing method to solve a biological recycling problem: breaking down PET with enzymes has so far only worked for so-called amorphous PET, which is used in things like fruit packaging. , but not for PET plastic bottles. with higher crystallinity.
Plastic-eating enzyme could remove billions of tons of landfill waste
Christian Sonnendecker et al, Low-carbon recycling of post-consumer PET plastic with a metagenomic polyester hydrolase, ChemSusChem (2021). DOI: 10.1002/cssc.202101062
Provided by the University of Leipzig
Quote: Enzyme breaks down PET plastic in record time (May 18, 2022) Retrieved May 19, 2022 from https://phys.org/news/2022-05-enzyme-pet-plastic.html
This document is subject to copyright. Except for fair use for purposes of private study or research, no part may be reproduced without written permission. The content is provided for information only.