By Savannah Mitchem

Researchers are converting our sludge, scraps and smog into higher-value products.

Nature is full of interconnected loops. Water travels in a never-ending cycle, going from the ground to the sky and back again. When living things die and decompose, elements such as carbon and nitrogen are absorbed by Earth’s crust and used to create new life. These systems of nature are closed loops, meaning they are self-sustaining, and they have no beginning or end.

Humans exist within these cycles; like all living things, we both influence and benefit from them. But the ways in which we currently manage our waste are anything but sustainable or circular. The emissions we produce and the plastics, devices, food and other waste we discard do not always get folded back into Earth’s natural cycles.

Instead, much of our waste is either left sitting in rapidly growing landfills, polluting the environment or both. Meanwhile, our emissions are accumulating in the atmosphere, driving rising global temperatures and damaging ecosystems. And despite our efforts so far, less than 10% of the approximately 7 billion tons of plastic waste ever generated has been recycled.

“With dedicated science, education and partnership, it’s only a matter of time before we achieve our vision for a more sustainable energy future.” — Meltem Urgun Demirtas, Argonne scientist

Researchers at the U.S. Department of Energy’s (DOE) Argonne National Laboratory are working toward a more regenerative future — one where Earth’s resources are circulated sustainably. In this type of economic system, called a circular economy, a product’s end of life is planned for at the design stage. This way, would-be waste becomes a valuable resource for creating new or refurbished products.

Argonne scientists are developing methods to recover and reuse precious metals and other valuable materials from batteries and devices at their end of life. They’re also developing technologies to turn waste into valuable commodities. And by collaborating with industry partners, other research institutions and local communities, they’re helping to bridge the gap between laboratory discovery and large-scale societal impact.

Closing the trash-to-treasure loop

A circular economy closes production loops in industry, turning waste into feedstock for the creation of new products. This means viewing landfills less like putrid, mountainous eyesores and more like massive treasure troves waiting to be mined for their stores of valuable materials.

“Plastic contains a lot of energy. It’s like prepurified crude oil, and it’s already out of the ground,” said Max Delferro, an Argonne chemist and group leader and Argonne’s Circular Economy lead. ​“In the future, as technologies improve, there could be a financial incentive to digging for plastic in landfills.”

Delferro and his team at Argonne are pioneering new and improved methods for recycling plastic waste. For example, they are using chemical tools called catalysts to convert plastic bags and films into higher-value products, such as lubricants and waxes. They’re also reimagining how plastic products are designed to begin with.

For example, as part of DOE’s Institute for Cooperative Upcycling of Plastics (iCOUP), Delferro and other scientists from Argonne and Cornell University developed a new method for recycling high-density polyethylene (HDPE), or Type 2 plastic. Their technique transforms postconsumer HDPE products into a new type of plastic material that can be recycled repeatedly without loss of quality.

Another team at Argonne is improving recycling techniques for batteries and microelectronic devices.

“What I like about recycling is that you start out with what looks like garbage — it’s dirty, it’s broken — and then you have shiny metal and other products coming out of the equipment at the end,” said Jeffrey Spangenberger, leader of Argonne’s Materials Recycling Research and Development group and director of the ReCell Center. ​“It’s hidden at first, but there’s a lot of valuable stuff in there.”

Located at Argonne, the ReCell Center is a national collaboration of industry, academia and national laboratories advancing battery recycling technologies. Recycling batteries and other devices reduces the demand for mining rare minerals used in batteries such as lithium, cobalt and nickel. Bringing these critical materials back into the production loop also lowers the cost of batteries for electric vehicles, which could play an important role in reducing our carbon dioxide (CO₂) emissions.

Even society’s stinkier waste streams can be used as valuable feedstock. Argonne scientist Meltem Urgun Demirtas is researching ways to recover resources from food waste and sludge generated from cities, wastewater treatment plants and industrial processes. In the lab, she and her team have experimented with waste from local restaurants, pig farms, breweries, cheese producers and even their own homes.

“My motivation is to clean up the world,” said Urgun Demirtas, who leads Argonne’s Sustainable Materials and Processes department. ​“Anything that nobody wants in their backyard or in their city is of interest to me.”

Urgun Demirtas and her colleagues are feeding these waste streams to colonies of highly diverse and resilient microorganisms. Through digestion, the communities of microorganisms can treat organic waste streams, such as wastewater and sludge, and convert them into fuels, including renewable methane and sustainable jet fuel.

And to close as many loops as possible, the nutrient-dense leftovers from these processes can be used as fertilizer or soil conditioner. Recovering nutrients from waste has the added benefit of preventing harmful algae blooms that they can cause if left unchecked in the environment.

Junhong Chen, lead water strategist at Argonne and a professor at the University of Chicago’s Pritzker School of Molecular Engineering, is also working to accelerate the creation of technologies for water treatment and resource recovery.

“Water is not just vital for sustaining our lives; it’s also needed for manufacturing products in virtually every industry,” said Chen, who serves as the co-principal investigator for Great Lakes ReNEW, a Regional Innovation Engine awarded by the U.S. National Science Foundation (NSF). ​“As long as water touches society, there will be a critical need and opportunity for a circular blue economy.”

Coordinated by the Chicago-based water innovation hub, Current, in partnership with Argonne and the University of Chicago, Great Lakes ReNEW will develop and deploy improved technologies for recovering critical minerals and nutrients from wastewater and purifying it of contaminants.

For instance, the team is developing a network of interconnected sensors across the Great Lakes region to monitor levels of different materials present in wastewater in real time. This information could help wastewater treatment plants optimize their facilities to process incoming waste, which can change day by day.

The science of deconstruction

A main challenge in developing any recycling or resource recovery method is to separate the valuable materials and components from the rest of the waste. It’s an even bigger challenge to separate them in a way that’s cost-effective and environmentally sustainable.

“We spent a hundred years developing our plastics to have very particular properties, and only in the last several years have we really started to think about how to take them apart responsibly,” Delferro said. ​“It’s an exciting time to be a scientist because we’re at the inception of a new science: the science of deconstruction.”

For example, plastic waste is generally not pure plastic. It often contains contaminants and additives (like dyes and flame retardants) that need to be separated out with series of catalysts. This is a complex science. So far, the best catalysts researchers have discovered for recycling plastics consist of rare and expensive metals.

Delferro and his colleagues are working to make effective catalysts from earth-abundant materials that can be mined in the U.S. His team is also collaborating with another group at Argonne to assess the potential environmental effects of the plastics they’re developing.

“We have to make sure that even when the biodegradable plastics break down, it won’t be toxic to the environment,” Delferro said. ​“There’s a lot to consider, and all of it feeds into a circular economy.”

The same is true for recycling batteries and microelectronics. ​“A lot of this waste is all chewed up or meshed together. In order to make recycling profitable, you need to find technologies to separate glass, plastic, metal, liquids and other materials using technologies that are cheap and easy to operate,” Spangenberger said.

Real-world recycling plants use a series of machines like shredders, strong magnets and furnaces to separate out different materials. Even when they involve the more delicate touch of artificially intelligent sorting robots, many of the existing processes to recover recyclable materials from electronic devices are inefficient, energy intensive or expensive.

Spangenberger and his colleagues are helping industry partners discover the most profitable and sustainable ways to approach their recycling processes.

For example, he and his team are collaborating with Toyota Motor Engineering & Manufacturing, North America, to explore the use of an innovative method developed by the ReCell Center for recycling EV batteries. The new approach — called direct recycling — separates entire components of the batteries, leaving them intact to be used again in another battery. This reduces the need for the expensive manufacturing processes used to create the components from scratch. In turn, the new approach could help reduce the nation’s dependence on other countries for battery materials.

The team is also building a pilot recycling plant at Argonne. The plant will allow the team to test new recycling technologies integrated with existing ones, and to scale up processes to be tested in real-world industrial conditions with real-world feedstocks.

Separation is also a major challenge in treating and processing organic waste — such as wastewater, sludge and food waste. This is because the waste streams are so varied and complex. In fact, separation accounts for up to 70% of the total cost to convert organic waste into fuels and other products. Argonne is developing advanced technologies to reduce the emissions and costs associated with organic waste separation.

The science of reconnection

One reason scientists like Urgun Demirtas are so interested in sludge and other organic waste is because it is rich in the element carbon. Carbon is the main component of many fuels because it releases large amounts of energy when it’s burned.

This is the same element that exists in the CO₂ molecules accumulating in the atmosphere and driving global warming. When we burn fossil fuels and release our CO₂ emissions, we are simultaneously harming Earth’s systems and surrendering large quantities of a valuable resource.

Argonne chemist Di-Jia Liu is working to connect the sources of our otherwise emitted carbon to industries that can use it as a raw material for some of the most-produced fuels and chemicals in the U.S. These include ethanol, acetic acid, ethylene and propanol, which are used in gasoline and as intermediate products for the chemical, pharmaceutical and cosmetics industries.

Liu and his team envision a future where all of the CO₂ we produce remains in the closed loop of our circular economy, gradually reduced from the atmosphere and infinitely reused. However, it is expensive and energy intensive to convert CO₂ to fuels and chemicals using existing technologies.

To make the process more affordable, Liu’s team is creating more efficient catalysts and developing a CO₂ conversion device called an electrolyzer. The device works at low temperatures and pressures compared with existing technologies, and it can turn on and off quickly without much energy loss. These features make it ideal for coupling with renewable energy sources such as wind and solar power, whose availability can be intermittent.

“To make this profitable in the near term, the idea is to use renewable energy to convert locally produced CO₂ into value-added chemicals and products for local consumption,” Liu said. ​“This eliminates the costs associated with transportation and distribution.”

Renewable energy is at the heart of scientists’ vision for a circular economy, but its widespread adoption depends on the development of affordable and efficient batteries to help smooth over intermittent energy supplies.

Here we see the interconnected production loops that comprise a circular economy. Improvements in battery recycling technologies make batteries cheaper. Cheaper batteries translate to more effective infrastructure for storing and using renewable energy. In turn, cheaper electricity reduces the cost of recycling CO₂ and other waste into higher-value materials. Improved recycling helps to recirculate recovered minerals, which lowers the cost of batteries even more. And the virtuous cycle continues.

These interdependencies can also make developing sustainable technologies and infrastructure challenging. ​“By the time we’ve mastered the recycling of one type of battery, a cheaper, more sustainable battery that requires a different recycling technique will be discovered,” Spangenberger laughed. ​“This progress is good, of course. It demonstrates that we are getting closer to our ultimate goal.”

Partnership and communication across industries and scientific disciplines are crucial for efficient development and implementation of these technologies. Collaborations like Great Lakes ReNEW and the ReCell Center help facilitate the validation of new approaches at different scales, accelerating their transition to market. They’re also connecting with academic institutions and local communities to foster an inclusive innovation ecosystem and educate the next generation of scientists, engineers and policymakers.

With full awareness of the challenges ahead, the Argonne researchers remain energized and optimistic.

“It took about 50 years to produce the large volumes of gasoline — and about 20 years to produce the large volumes of corn ethanol — that meet our fuel needs today,” Urgun Demirtas said. ​“With dedicated science, education and partnership, it’s only a matter of time before we achieve our vision for a more sustainable energy future.”

In addition to the NSF, this research is supported by DOE’s Office of Science’s Office of Basic Energy Sciences and DOE’s Office of Energy Efficiency and Renewable Energy’s offices of Bioenergy Technologies, Vehicle Technologies, Advanced Materials and Manufacturing Technologies, and Industrial Efficiency and Decarbonization.

Argonne National Laboratory seeks solutions to pressing national problems in science and technology by conducting leading-edge basic and applied research in virtually every scientific discipline. Argonne is managed by UChicago Argonne, LLC for the U.S. Department of Energy’s Office of Science.

The U.S. Department of Energy’s Office of Science is the single largest supporter of basic research in the physical sciences in the United States and is working to address some of the most pressing challenges of our time. For more information, visit https://​ener​gy​.gov/​s​c​ience.