As more waterways contend with algae blooms and pollution caused by minerals from agricultural runoff and industrial manufacturing processes, new methods of removing pollutants like phosphate, copper, and zinc are emerging across fields.
While solutions exist, they tend to be costly and can only be used once. However, a specialised sponge created by researchers at Northwestern University that slurps up pollutants and then releases them as desired may present a reusable, low-cost solution.
The sponge, coated with nanoparticles that are apt for pollutants, can collect metals like zinc, copper, and phosphate. In previous iterations, it has successfully pulled lead, microplastics and oil from lakes and oceans. When exposed to different pH levels, it releases these valuable resources.
In a paper published in the American Chemical Society journal Environmental Science & Technology Water, researchers define a method to tailor their platform to specific Chicago pollutants and then selectively release them, giving resources that typically must be mined a potential for a second life.
“The technology can be used as a universal sorbent or ‘catch-all,’ or it can be tailored to certain groups of contaminants like metals, plastics or nutrients,” said principal investigator Vinayak Dravid.
Dravid is the Abraham Harris Professor of Materials Science and Engineering at Northwestern’s McCormick School of Engineering and a faculty affiliate of the Paula M. Trienens Institute for Sustainability and Energy. He is also the founding director of the Northwestern University Atomic and Nanoscale Characterization (NUANCE) Center and the Soft and Hybrid Nanotechnology Experimental (SHyNE) Resource. He is also the associate director of global programs at the International Institute of Nanotechnology.
What’s with the sponge?
In its first iteration, the sponge platform was made of polyurethane and coated with a substance that attracted oil and repelled water. The newest version is a highly hydrophilic (water-loving) cellulose sponge coated with particles tailored to other pollutants. The sponge platform works so effectively because its pores provide a large surface area where pollutants can attach.
At times, Dravid has referred to the technology as a “Swiss Army knife” because of its versatility and ability to be used repeatedly. He co-founded NU startup Coral Innovations (formerly MFNS-Tech) to begin the process of commercialising the sponge-based technology for environmental remediation.
A one-two P(h)unch
Stormwater treatment equipment manufacturer StormTrap, LLC, learned about the platform and approached the team, asking about three specific pollutants heavily impacting Chicago. Hoping to add absorbent materials to their portfolio, StormTrap representatives asked if Dravid could reduce the concentration of pollutants to untraceable amounts.
The Environmental Protection Agency sets levels for minerals based on human health that are at times higher than the amount considered safe from an environmental perspective, typically setting drinking water limits in the parts per million range when preventing algae blooms and other environmental impacts would require much smaller concentrations.
Developing the platform to capture copper, zinc, and phosphate was relatively easy. Kelly Matuszewski, a PhD student in the Dravid group and the paper’s first author, was tasked with determining a method to recover the resources. As mines’ stores of phosphate and metals are depleted, this second step is becoming critical.
“We can’t just keep flushing these minerals down the toilet,” Matuszewski said. “We need to understand how they interact and find ways to utilise them.”
Matuszewski found that lowering the pH flushes metals out of the sponge. Once copper and zinc are removed, the pH is raised, at which point phosphate comes off the sponge. She found that even after five cycles of collecting and extracting minerals, the sponge worked just as well, and she was able to deliver water with untraceable amounts of pollutants.
Matuszewski is a finalist in the FoundHer Spotlight, a competition for early career women scientists facilitated by Northwestern’s Querrey inQbation Lab. She will pitch on March 5 to the Northwestern Women’s Board, competing against seven other researchers.
Taking it to the storm drains
The partnership with StormTrap, LLC has allowed the team to assess the technology’s effectiveness and move quickly from the lab to the industry. Using the platform in real-life scenarios will be an essential next step, as Matuszewski was working in a controlled environment where each pollutant had the same relative concentration. The next phase will help them determine the amount of minerals a sponge can hold and allow them to partner with other Northwestern researchers working on creating cleaner waterways.
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