Growing to more than 2cm long, mealworms are the larval stage of the mealworm beetle. Scientists have known for some time now about their ability to eat certain plastics, and researchers are now learning more about what's going on inside mealworms and replicating the process outside them.
It takes around 3,000 to 4,000 mealworms about a week to eat one Styrofoam coffee cup, and it's the bacteria living in their guts that break down the plastic, says Anja Malawi Brandon, a PhD candidate at Stanford University researching the subject.
When mealworms eat polystyrene -- the material used in Styrofoam, and often found in packaging -- they excrete half of it as carbon dioxide, and some as partially degraded particles, raising concerns they could add to the growing problem of microplastics -- tiny pieces of plastic that can end up in the food chain. But harnessing their biology could present new opportunities for how we deal with waste plastic.
Brandon, a plastics and bioplastics sustainability expert, was part of a team that last year published research showing that mealworms could eat polystyrene, as well as polyethylene -- one of the most widely used plastics in the world, found in everything from shopping bags to detergent bottles.
It also showed that when eating polystyrene, the mealworms excreted a flame retardant that is sometimes added to the plastic. That meant the toxic chemical didn't accumulate inside the mealworms, so it wouldn't be passed up the food chain if they were used as a protein-rich food for livestock like chickens and pigs.
Further research has now isolated the plastic-eating bacteria found in the mealworms' guts and grown them outside of the mealworm.
"Interestingly, the bacteria we identified are not crazy new, unheard of bacteria -- they're bacteria that have been associated with the breakdown of other environmental pollutants before," Brandon tells CNN.
"It shows that in the right environment these already-known bacteria are capable of plastic degradation," she continues. "This potentially means that other bacteria that are known to fortuitously break down other chemicals could break down plastics under the right conditions."
Brandon says degrading plastic with bacteria outside the mealworm is currently slower than the rate a mealworm is capable of, but under the right conditions, the degradation is "more rapid than other bacterial systems to date." She cannot share some details -- including the names of the bacteria -- as the research has not yet been published.
A natural recycling solution?
Plastic pollution is one of the most pressing environmental issues. A recent report from The Pew Charitable Trusts projected the volume of plastic entering the ocean could nearly triple to 29 million metric tons per year by 2040 -- the equivalent of 50 kilograms for every meter of the planet's coastline.
It also said there was "no single solution," but that "an ambitious recycling strategy" could slash 31-45% of plastic pollution.
Brandon says that for mealworms to be a viable recycling solution there would need to be a system to collect and treat the partly digested plastic they excrete. Using the bacteria in bioreactor vats instead could be easier to control and would leave no plastic residue. There's even the potential to use bacteria to break down plastics into monomers, the building blocks for other plastics.
Ramani Narayan, distinguished professor in chemical engineering and materials science at Michigan State University, says the science behind the Stanford research is "great," but cautions against extrapolating it into a solution for treating waste plastic.
"(Using mealworms is) not going to be a solution until you can say how you can integrate it into existing waste management infrastructures -- and that's where I see the big disconnect," he says, pointing out that dealing with all our plastic waste would require a vast number of mealworms.
Proven industrial processes to recycle polystyrene and polyethylene already exist, he says, adding that opportunities lie not in technology but in the collection and recovery of these plastics.
As for biological solutions, Narayan advocates designing plastics that can be composted by microbes alongside other biodegradable solids in existing waste management environments. "You don't want to change the [waste management] ecosystem; you want to harness the ecosystem to help you manage the waste," he says.
For now, Brandon's tests with the bacteria continue. "We're still a little way off from doing it at scale," she says, "but with our new research ... we have developed a system that will enable us to move to this future a lot faster. Hopefully this will be a viable technology."
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September 10, 2020 at 03:56PM
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Could unlocking the mystery of the mealworm's gut help solve our plastic crisis? - CNN
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