Enzymes could unlock biological recycling of difficult plastic waste
They are durable, cheap and everyday life is now hardly imaginable without them: plastics. More then 400 million metric tons are produced every year. As a large proportion is only insufficiently recycled, the environmental burden caused by plastic waste is increasing.
Plastics have become an integral part of modern life, with over 400 million metric tons produced annually. However, the majority of plastic waste is only partially recycled, leading to growing environmental concerns. Researchers at the University of Greifswald are exploring the potential of enzymes to break down difficult-to-recycle plastics into their individual chemical building blocks, making them available for reuse in new products.
Two teams from the university have published their findings in Nature Chemical Biology and Nature, highlighting the promising role of enzymes in the biocatalytic depolymerization of plastics.
One significant breakthrough is the successful depolymerization of polyethylene terephthalate (PET), used in beverage bottles and textiles, under mild conditions. Enzymes can selectively break down PET into its building blocks, which can then be utilized to produce new plastics. This method could potentially enable plastic to be used repeatedly, reducing waste.
Researchers have also identified enzymes capable of breaking down polyurethanes, found in products like mattresses, insulation materials, and athletic shoes. In another article, they determined which enzyme families are most effective in decomposing polyurethanes and polyamides (nylon). They also discussed optimizing these enzymes through protein engineering to enhance their efficiency in recycling processes.
Despite these advancements, the team from Greifswald cautions against premature conclusions regarding the biological degradation of plastics. They criticize claims of certain bacteria or enzymes breaking down plastics like polyethylene (PE) or polyvinyl chloride (PVC), which are more challenging to degrade biologically compared to PET, PU, or nylon.
Often, insufficient research, inadequate trials, or misinterpretation of results have contributed to these false claims. The authors emphasize the need for rigorous polymer characterization, appropriate controls, and quantitative analyses to reliably identify the microorganisms and enzymes capable of breaking down particularly difficult-to-recycle plastics.
The researchers have outlined specific recommendations for conducting experiments, from precise plastic characterization to suitable controls and quantitative analyses. These guidelines aim to help identify the microorganisms and enzymes responsible for breaking down challenging plastics, paving the way for reliable biological recycling procedures.
In the long term, these findings could contribute to the development of biological recycling methods for other plastics and facilitate the recovery of valuable raw materials from plastic waste. By reusing these materials in new products, they can be returned to the product cycle, reducing the environmental impact of plastic waste.
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