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Soaking Up Chicago’s Stormwater Pollution

New Environmental Remediation Technology to Clean Local Waterways and Capture Nutrients and Metals for Reuse

Arleigh Truesdale | March 8, 2024
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The copper, zinc, and phosphorus wading through Midwestern waterways tell the story of the region’s rich industrial and agricultural heritage. These pollutants also signal an urgent need to clean up stormwater from cities in the area like Chicago that cause long-term environmental harm as they flow downstream.

Regionally specific problems require regionally specific solutions. A team of Northwestern researchers has designed the ‘PEARL’ media, a sponge-based platform with a special coating that has an affinity for pollutants found in the Chicago area. With $250,000 in seed grant funding from the Paula M. Trienens Institute for Sustainability and Energy, the team is partnering with stormwater treatment equipment manufacturer StormTrap, LLC to test PEARL’s performance in real-world conditions.


Trienens Institute Faculty Affiliate Vinayak Dravid, Abraham Harris Professor of Materials Science and Engineering, and his research group have a long history of developing reusable absorbent membranes. This technology has successfully pulled lead from water as well as microplastics and oil from lakes and oceans. PEARL is the next iteration of the “Swiss Army knife” or “platform” technology whose base structure remains consistent while unique coatings are applied to the surface to adsorb context-specific pollutants. In the case of Chicago, the coating has been designed to filter out copper, zinc, and phosphorus.

“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,” Dravid explained.


Professor Vinayak Dravid

Dravid is the project’s Principal Investigator, the Founding Director of the Northwestern University Atomic and Nanoscale Characterization (NUANCE) Center as well as the Soft and Hybrid Nanotechnology Experimental (SHyNE) Resource, an NSF-NNCI Node. The research team also includes senior research faculty Dr. Vikas Nandwana and Materials Science and Engineering PhD students Kelly Matuszewski, Benjamin Shindel, and Elias Kallon.

Environmental remediation—the removal of harmful contaminants from soil, water, and air—is vital to improving ecological and human health and reclaiming valuable land. Across the country, remediation has become more of a priority. The United States Environmental Protection Agency keeps a list of highly contaminated ‘Superfund’ sites queued for clean-up, including a handful in the Chicago area.

Yet, most remediation technology involves the use of single-use materials that create waste, have limited absorption capacity, and are not cost-effective. The new PEARL media, on the other hand, can be reused.

PEARL technology has already proven its effectiveness. Looking to add absorbent materials to their stormwater treatment portfolio, StormTrap LLC seeded Dravid’s first trials with PEARL at Northwestern in 2023. Now, this translational demonstration project will take PEARL out of the lab to test its compatibility with local infrastructure and commercial scalability.

“StormTrap will bring the industrial experience to the project and expertise about how to adapt the innovation to the local context and implement it in a realistic environment,” said Dravid. The PEARL sponge will be subject to repeated exposure to different cycles and intensities of water flow and dryness that mimic rainfall trends in Chicago.

Earlier versions of Dravid’s sponge-based platforms have been commercialized through various start-up companies such as MFNS-Tech, co-founded by Dravid and Dr. Nandwana, which focuses on cleaning up oil and other toxins from water. If PEARL survives the stress-test, it has the potential to create novel ways for StormTrap to collect dissolved contaminants from stormwater runoff.

Repurpose, Remediate, Recover, Recycle

Up until now, sponge-based remediation has soaked up different types of pollutants using different sponges. This makes it possible to capture the contaminants—oil, heavy metals, phosphate—for possible reuse. Part of the problem PEARL is trying to solve is how to filter out multiple contaminants at once and in one place. “We want to be able to recover what we capture. Phosphorus is a non-renewable resource, so if we can extract it then we can move toward a more circular and sustainable lifecycle for these materials,” said Matuszewski.

During the demo project, Matuszewski plans to explore the use of a phased remediation approach to isolate the contaminants one at a time.

Chicago’s salvaged pollutants have the potential to be part of a climate-positive future. “With the growth of the transition to renewable energy, there is going to be a shortage of metals needed to build the infrastructure. If we can recover metal and phosphorus from something that would otherwise be considered waste, we have a new source of valuable resources,” said Dravid.

But before PEARL can make its market debut, the research team will perform a techno-economic analysis to understand how other industrial partners perceive the uncertainties, risks, and benefits of the technology as well as the time it might take to be market-ready.

Dravid and his group will also investigate the holistic cost and environmental impact of scaling up the production and application of the PEARL media. What, for instance, is the carbon footprint of manufacturing enough of the sponge membrane to meet the pollution absorption needs of the entire city of Chicago?

For this, Dravid plans to partner with other Northwestern research groups with expertise in life cycle assessment and other areas. “There’s an opportunity here to collaborate with other Trienens Institute Faculty Affiliates and colleagues who are involved in fluid mechanics or modeling to help us optimize the architecture and porosity of the PEARL filter,” said Dravid.

“There is a gap between lab-level research that happens at the nanoscale and its application to gigaton problems. This seed funding from the Trienens Institute is bridging that gap.” - Professor Vinayak Dravid

Dravid and StormTrap are setting an example of the value of industry-academic collaboration for tackling complex environmental challenges. “There is a gap between lab-level research that happens at the nanoscale and its application to gigaton problems,” Dravid remarked. “This seed funding from the Trienens Institute is bridging that gap.”

Water pollution is growing in importance for Chicago and the Great Lakes region more broadly. Earlier this year, the Great Lakes Water Innovation Engine (ReNEW) received $160 million from the National Science Foundation with a goal of amplifying resource recovery from societal waste streams. Northwestern is a core partner of the initiative.

The two-year demonstration, “Assessing the Commercial Viability of PEARL Media in Stormwater Treatment: Translating Promises to Prospects,” officially began March 1, 2024.