In the reactor of one recent MTU demonstration, shown here, parts of the decomposed plastics are subjected to high heat and oxygen-free conditions, a process called pyrolysis.
Caden Staley/Michigan Tech University
That uncertainty was key. The Defense Advanced Research Projects Agency (DARPA) supports high-risk, high-reward projects, which means there's a good chance that any individual effort will fail. But if the project succeeds, it could represent a true scientific breakthrough. “Our goal is to move from disbelief: 'You've got to be kidding me. What do you want to do?' to 'Actually, that might be possible,'” says Leonard Tender, a DARPA program manager overseeing the plastic-waste project.
The problems associated with plastic production and disposal are well known. According to the United Nations Environment Programme, the world generates around 440 million tonnes of plastic waste per year. Much of it ends up in landfills and oceans, where microplastics, plastic pellets and plastic bags pose a threat to wildlife. Many governments and experts agree that production must be reduced to solve the problem, and some countries and US states have even introduced policies to encourage recycling.
Scientists have also experimented with different species of plastic-eating bacteria over the years, but DARPA is taking a slightly different approach, looking for a compact, portable solution to use plastic to produce something else entirely: food for humans.
Initially, the effort “felt more like science fiction than something that could actually work.”
The goal, Teftman hastens to add, is not to get humans to eat plastic. Rather, he hopes that his plastic-eating microbes will themselves prove suitable for human consumption. Teftman thinks the bulk of the project can be completed in a year or two, but the food phase could take longer. His team is currently conducting toxicity tests, after which they will submit their results to the Food and Drug Administration for review. Even if all goes well, more challenges lie ahead. “There's an element of discomfort that I think we'll have to overcome,” Teftman said.
The military isn't the only team working to turn microbes into nutrients: From South Korea to Finland, a handful of researchers and companies are investigating whether microbes could help feed a growing global population in the future.
DARPA's call for proposals aimed to solve two problems at once, Tender said. First, the agency wanted to reduce so-called supply chain vulnerabilities: during wartime, the military needs to transport supplies to troops in remote locations, threatening the safety of the people inside the vehicles. Additionally, the agency wanted to end the use of dangerous incinerators as a means of disposing of plastic waste. “It's a huge burden to responsibly remove these waste materials from those sites,” Tender said.
Research engineers working on the MTU project will take feedstock samples from the pyrolysis reactor and upcycle them into fuels and lubricants.
Caden Staley/Michigan Tech University
Michigan Tech's system starts by mechanically shredding the plastic, then transferring it to a reactor where it's soaked in hot ammonium hydroxide. Plastics like PET, commonly used in disposable water bottles, break down at this point. Other plastics used in military food packaging, like polyethylene and polypropylene, are sent to a separate reactor where they're exposed to even higher temperatures and a lack of oxygen.
Under these conditions, polyethylene and polypropylene are converted into compounds that can be upcycled into fuels and lubricants. David Schonard, a chemical engineer at Michigan Technological University who oversaw this part of the project, has founded a startup called Resurgent Innovation to commercialize some of this technology. (Schonard says other members of the research team are working on additional patents related to other parts of the system.)
