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Big Idea

Plastic isn’t getting recycled. Why not feed it to microbes?

Fermentation could turn discarded water bottles into something valuable.

By Adina Solomon

Plastic is ridiculously convenient. It’s strong, light, and can be molded into any shape. It easily holds liquids, from water to laundry soap.

But the same characteristics that make plastic so useful also make it difficult to dispose of. Only 9% of plastic waste ever produced has been recycled. That leaves billions of metric tons languishing in landfills and the environment, including the ocean. To upcycle plastic before it becomes waste, one researcher is turning to the process we use to make pickles and beer: fermentation.

The problem

Breaking down plastic isn’t just hard to do, it’s expensive. Recycling plastic lowers its quality, says Eric Gilbert, a biology professor at Georgia State University in Atlanta. Compared with virgin, never-molded plastic, recycled plastic is not as strong. (Glass and metal, by contrast, can be recycled infinitely without losing quality.) Plastic containing food residue also can’t be recycled unless it’s first cleaned.

As a consequence, about 20% of plastic accepted by recycling facilities is not cost-effective enough to separate. Bales of this scrap plastic — which contain mixtures of polyester, polypropylene, and other plastic types — usually are so worthless that they go to a landfill.

Only 9% of plastic waste ever produced has been recycled. That leaves billions of metric tons languishing in landfills and oceans.

So product manufacturers rarely have a financial incentive to work with recycled plastics, Gilbert says. They end up creating new plastic.

The solution

Instead of sending all our plastic refuse to a traditional recycling plant, Gilbert proposes that we could feed it to yeast microbes. The result would be to upcycle plastic, rather than downcycle it — repurposing those discarded materials into a product of higher value than the original. Upcycling is common in the art world and in fashion, where apparel companies make bags and other accessories from scraps of clothing fabric.

And yeast microbes, Gilbert contends, are equipped to do the job. In his lab, Gilbert and his team break plastic into bite-sized molecules that are small enough for yeast microbes to eat. As the microbes consume those plastic molecules and grow, they produce fatty acids that can be sold for use in all sorts of commercial products, including paint, solvent, and industrial lubricants. The fermentation process is similar to the one that breweries use, except that instead of making beer, it makes fatty acids.

So far, Gilbert has experimented with transforming polypropylene, nylon, and polyesters into fatty acids. He also believes the process will work on food-contaminated plastics and products made of plastic mixes.

And he has found a partner in Dalton, a Georgia city in the foothills of the Blue Ridge Mountains that serves as the production center for 95% of the carpet manufactured in the United States. Since 2015, Gilbert has worked with the Dalton-based nonprofit Carpet America Recovery Effort (CARE), which supplies Gilbert’s lab with plastic-based carpet discarded by consumers.

Currently, only 5% of the carpet manufactured in the U.S. gets recycled, says Bob Peoples, executive director of CARE. The rest makes up nearly 2%, by weight, of all of the trash that ends up in landfills. Gilbert’s lab could turn that discarded carpet into commercial products such as paint. “Chemical recycling is really coming on as an important approach to dealing with plastic waste around the world,” Peoples says. More widespread upcycling with methods like Gilbert’s could also provide a financial boost for carpet recycling businesses, which operate on slim margins.

The challenge

Right now, Gilbert and his colleagues in the Georgia State lab can harvest just a small amount of fatty acids from their microbes. Gilbert says that yield would need to increase tenfold to capture the attention of commercial interests. To that end, he’s collaborating with Southeastern Biochemicals, a Georgia startup working to build a refinery that converts plastic waste into consumer products.

The big picture

Plastic waste is too big a problem to solve with yeast microbes alone. Plastic can take hundreds of years to break down, if it does at all, meaning much of our trash will outlive us. Water bottles will take 450 years to fully decompose; toothbrushes will take 500 years. But Gilbert hopes his research will create enthusiasm in the scientific community for developing alternative ways of repurposing plastic. Look at agricultural waste, Gilbert says. Instead of rotting in a landfill, it is upcycled to make renewable bioethanol. What if that thinking were applied to plastic?

“This is a terribly difficult problem to work on,” he says. “It’s stupid hard… [But] let’s see if we can do anything that would be useful. And maybe if we do, we’ll get other people excited about it.”

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Adina Solomon is a writer based in Atlanta. She has written for The Washington Post, The Guardian, National Geographic, and others. 


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