Enlarge (credit: Derek Berwin)

Our planet is choking on plastics. Some of the worst offenders, which can take decades to degrade in landfills, are polypropylene—which is used for things such as food packaging and bumpers—and polyethylene, found in plastic bags, bottles, toys, and even mulch.

Polypropylene and polyethylene can be recycled, but the process can be difficult and often produces large quantities of the greenhouse gas methane. They are both polyolefins, which are the products of polymerizing ethylene and propylene, raw materials that are mainly derived from fossil fuels. The bonds of polyolefins are also notoriously hard to break.

Now, researchers at the University of California, Berkeley have come up with a method of recycling these polymers that uses catalysts that easily break their bonds, converting them into propylene and isobutylene, which are gasses at room temperature. Those gasses can then be recycled into new plastics.

Enlarge (credit: Olga Pankova/Moment via Getty Images)

In 2019, an agency within the US Department of Defense released a call for research projects to help the military deal with the copious amount of plastic waste generated when troops are sent to work in remote locations or disaster zones. The agency wanted a system that could convert food wrappers and water bottles, among other things, into usable products, such as fuel and rations. The system needed to be small enough to fit in a Humvee and capable of running on little energy. It also needed to harness the power of plastic-eating microbes.

“When we started this project four years ago, the ideas were there. And in theory, it made sense,” said Stephen Techtmann, a microbiologist at Michigan Technological University, who leads one of the three research groups receiving funding. Nevertheless, he said, in the beginning, the effort “felt a lot more science-fiction than really something that would work.”

That uncertainty was key. The Defense Advanced Research Projects Agency, or DARPA, supports high-risk, high-reward projects. This means there’s a good chance that any individual effort will end in failure. But when a project does succeed, it has the potential to be a true scientific breakthrough. “Our goal is to go from disbelief, like, ‘You're kidding me. You want to do what?’ to ‘You know, that might be actually feasible,’” said Leonard Tender, a program manager at DARPA who is overseeing the plastic waste projects.

Enlarge / Some of the waste material that ends up part of these bricks. (credit: Seamus Daniel, RMIT University)

Researchers at the Royal Melbourne Institute of Technology (RMIT) in Australia have developed special “energy-smart bricks” that can be made by mixing clay with glass waste and coal ash. These bricks can help mitigate the negative effects of traditional brick manufacturing, an energy-intensive process that requires large-scale clay mining, contributes heavily to CO₂ emissions, and generates a lot of air pollution.

According to the RMIT researchers, “Brick kilns worldwide consume 375 million tonnes (~340 million metric tons) of coal in combustion annually, which is equivalent to 675 million tonnes of CO₂ emission (~612 million metric tons).” This exceeds the combined annual carbon dioxide emissions of 130 million passenger vehicles in the US.

The energy-smart bricks rely on a material called RCF waste. It mostly contains fine pieces of glass (92 percent) left over from the recycling process, along with ceramic materials, plastic, paper, and ash. Most of this waste material generally ends up in landfills, where it can cause soil and water degradation. However, the study authors note, “The utilization of RCF waste in fired-clay bricks offers a potential solution to the increasing global waste crisis and reduces the burden on landfills."

Enlarge / All these pieces more or less pop apart after a brief chemical treatment. (credit: Israel Sebastian.)

For years, the arguments against renewable power focused on its high costs. But as the price of wind and solar plunged, the arguments shifted. Suddenly, concerns about the waste left behind when solar panels hit end-of-life became so common that researchers at the US's National Renewable Energy Lab felt compelled to publish a commentary in Nature Physics debunking them.

Part of the misinformation is pure nonsense. The primary ingredients of most panels are silicon, aluminum, and silver, none of which is a major environmental threat. Solar panels also have a useful lifespan of decades, and the vast majority of those in existence are less than 10 years old, so waste hasn't even become much of a problem yet. And, even once these panels age out, recycling techniques are available.

Perhaps the only realistic concern is that existing recycling technologies rely on nitric acid and can produce some toxic waste. But a group of researchers from Wuhan University have figured out an alternative means of recycling that avoids the production of toxic waste and is more energy-efficient as a bonus.