Nanotechnology

Mushrooms make food from plastic which is difficult to recycle

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April 17, 2023

(Nanowerk News) Polypropylene has long been the head-scratching conundrum of recycling. Common plastics, which are used in a wide range of products from packaging and toys to furniture and fashion, account for around 28 percent of the world’s plastic waste, but only 1 percent is recycled.

Now, thanks to the efforts of researchers at the University of Sydney, the recalcitrant polymer may have found its match. Published in npj: Material Degradation (“Biodeterioration of polypropylene pre-treated by Aspergillus terreus And Engyodontium album), two types of fungi commonly used to successfully degrade polypropylene in laboratory experiments. plastic biodegradation by fungi Plastic before and after the fungus is applied. (Image: University of Sydney)

Usually found in soil and plants Aspergillus terreus And Engyodontium album was able to break down polypropylene after pre-treating it with UV light or heat, reducing the plastic by 21 percent over 30 days of incubation, and by 25-27 percent over 90 days.

“Polypropylene is a common plastic used to make a wide variety of everyday products such as food containers, clothes hangers and cling film, but has a recycling rate of just one percent, meaning it is overrepresented in plastic waste and pollution globally,” said lead author of the study from the University of Sydney’s School of Chemical and Biomolecular Engineering, PhD student Amira Farzana Samat.

The researchers hope their method may one day reduce the massive amount of plastic polluting the environment and lead to a better understanding of how plastic pollution biodegrades naturally under certain conditions.

“Plastic pollution is by far one of the biggest waste problems of our time. Most is inadequately recycled, meaning it often ends up in our oceans, rivers and landfills. An estimated 109 million tons of plastic pollution has accumulated in the world’s rivers and 30 million tons are now in the world’s oceans – with sources predicting this will soon exceed the total mass of fish,” said Ms Samat.

The researchers say polypropylene is rarely recycled because of its short life as a packaging material and because it is often contaminated by other materials and plastics, necessitating new recycling methods that have minimal environmental impact.

PhD supervisor Mrs Samat, Professor Ali Abbas from the School of Chemical and Molecular Engineering and Chief Circular Engineer at Circular Australia said: “Despite large-scale production and consumption of plastics, there has been little attention paid to degradation of plastics in environmental conditions, and our understanding of how plastic can be degraded is still limited.”

“One big question that arises from our results is – what naturally occurring conditions can accelerate the degradation of plastics? We seek to further explore the role of biological processes offered by fungi and other microorganisms.”

Professor Dee Carter, an expert in mycology – the study of fungi – in the School of Life and Environmental Sciences and co-author of the study said: “Fungi are very versatile and are known to break down almost any substrate. This superpower is due to the production of powerful enzymes, which are secreted and used to break down substrates into simpler molecules which can then be absorbed by the fungal cells.

“Most of the time, these fungi have evolved to break down wood materials, but this ability can be reused to attack other substrates – this is why we find them growing on all kinds of man-made materials such as carpet, painted furniture, grout around tiles, showers. curtains, upholstery and even car headlights.

“Recent studies show some fungi can even degrade some ‘forever chemicals’ like PFAS, but the process is slow and not well understood. There is also evidence that the amount of plastic accumulating in the oceans is less than would be expected based on production and disposal rates, and there is speculation that some of this ‘lost’ plastic may have been degraded by marine fungi.”

How the process works

Polypropylene in various forms is initially treated by one of three separate methods: ultraviolet light, heat, and Fenton’s reagent – an acidic solution of hydrogen peroxide and ferrous iron that is often used to oxidize contaminants.

In petri dishes, the fungi were applied separately as a single culture to the treated polypropylene. The validity of the biodeterioration was then confirmed through microscopy techniques. Although the study did not evaluate how the plastic was degraded by the fungus or whether it was metabolized, the researchers hope to carry out further studies to determine the type of biochemical processes that occur.

The next step

Professor Abbas believes the low rate of recycling of plastics globally presents a “huge plastic circularity gap”: “We need to support the development of disruptive recycling technologies that increase plastic circularity, especially technologies driven by biological processes such as those in our research. . It is important to note that our study has not performed any optimization of experimental conditions, so there is a lot of room to further reduce this degradation time.”

The researchers will now explore increasing overall efficiency in degrading polypropylene before seeking investment to scale the technology and develop small-scale pilot prototypes for commercialization.

Since completing the research, the team has isolated other microorganisms from the marine environment and used a similar process to degrade marine plastic debris, with initial results indicating higher degradation.

Ms Samat said: “We are very excited about this and have started looking into ways to enhance the degradation process using these microorganisms. Watch this space.”



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