Microplastics are pervasive across the Great Lakes, with groups like the International Joint Commission pushing for this pollution to be deemed a “Chemical of Mutual Concern” under the Great Lakes Water Quality Agreement.
Achieving this designation would compel Canadian and U.S. authorities to take coordinated action for the strategic management of microplastics. A report from IJC’s Great Lakes Science Advisory Board Work Group on Microplastics further proposes using them as an indicator of ecosystem health, similar to metrics utilized for nutrient pollution or invasive species.
Meanwhile, regional wastewater treatment plants in the region are challenged to remove microplastics, which come in a variety of sizes and chemical types and are not easily broken down by existing methods.
With microplastic particles being so small, they often go undetected during facility operations, said Allison Fore, public and intergovernmental affairs officer for The Metropolitan Water Reclamation District of Greater Chicago, a government agency responsible for wastewater treatment for Cook County.
Treatment facilities like the Stickney Water Reclamation plant in Cook County, Ill., are challenged to remove microplastics from wastewater. Photo: Metropolitan Water Reclamation District“The extent of their occurrence remains unclear, largely because standardized analytical methods for quantifying microplastics are lacking,” Fore said in an email. “Capturing and removing microplastic particles require a specialized filtration system, such as membrane bioreactors, nano-filters or other advanced technologies. Retrofitting existing plants with these systems demands significant upfront investment, often millions of dollars.”
Using current methods, wastewater plants effectively remove a high percentage of microplastics – typically between 85% and 95% – during routine operations, added Fore. These tiny plastic particles are most often captured by screens, grit removal tanks or primary clarifiers. Clarifier tanks use a gravity-based process to clump and settle microplastics, pulling heavier masses to the bottom for effective removal.
Although MWRD currently lacks local data on microplastic concentrations in its reclaimed water, Fore cited studies indicating that about 5% to 10% of incoming microplastic particles are released in the final treated effluent.
“Results are highly variable among treatment plants and regions,” Fore said. “In contrast, atmospheric deposition and stormwater runoff are among the primary sources of microplastics entering the Great Lakes, along with the wastewater treatment plants that discharge directly into the lakes. However, data on these contributions remains limited.”
A work in progress
By name alone, microplastics are difficult to detect in wastewater, note experts. Full removal of these tiny pollutants demands upgrades in infrastructure and technology, with potential fragmentation into virtually untreatable nanoplastics complicating every solution.
The Great Lakes being a plastics production hub makes the region uniquely susceptible to large-scale microplastics pollution, noted Andrea Densham, senior policy advisor for nonprofit conservation group Alliance for the Great Lakes.
In this environment, screened and skimmed solid is typically sent to landfills, while sludge from clarifiers can be processed into biosolids. At the same time, waste treatment officials are determining how to handle a pollutant that, beyond its base polymer, is rife with chemical additives that can leach into waterways.
“It’s a work in progress, in terms of systems doing this work in the best and most cost-efficient way,” said Densham. “Just using screens won’t catch all (the microplastics). Then money becomes an issue when using those other technologies.”
Treated sewage sludge must meet strict regulatory standards for pathogen and pollutant content, considering they provide essential nutrients to a variety of food crops. While the presence of microplastics in biosolids is known to affect soil health, the precise ecological impact of these contaminants is still a subject of research, said Timothy Hoellein, a biology professor at Loyola University Chicago.
Cities like Chicago with combined sewer systems collect both sanitary sewage and stormwater runoff in a single set of pipes. During heavy rain and overflow events, excess sewage is discharged directly into waterways, releasing millions of microplastic pieces that would otherwise have been captured by treatment plants.
Since there are no clear federal regulations governing these particles, questions surrounding microplastic treatment during normal wastewater output still persist, said Hoellein.
“Microplastics have been studied for the last 15 years, but it’s still a new problem, and not included as part of drinking water and wastewater standards,” Hoellein said. “They’re not a regulated pollutant.”
Finding a better way
In the U.S., the Microbead-Free Waters Act of 2015 – which bans plastic microbeads in rinse-off cosmetics – is the only comprehensive federal regulation against microplastics. States like California have adopted a dual strategy to combat microplastic pollution, working both to reduce waste at its source and educate the public on the pollutant’s environmental dangers.
On the innovation side, treatment plants could implement sand filtration, a process that physically traps microplastics as water flows through layers of sand or other porous materials. Technologies like biological filtration – where algae and other living organisms degrade microplastics – are still in the early stages of development.
“The work around microplastics feels so big, because it’s entrenched with our habits and economy,” says Hoellein. “But you can look at individual categories and solutions, like the Microbeads Act. Just keep an open mind to the spirit of possibility, and we can see results.”
Fore of Chicago-based MWRD emphasized public awareness as a means of mitigating microplastics before they can overwhelm treatment equipment.
“Source control is the most effective way of addressing complex contaminants,” said Fore. “This means eliminating or reducing use of single-use plastics and personal care products containing microbeads, recycling plastics instead of discarding them, and minimizing driving to reduce tire wear, which is a major source of microplastics in urban runoff.”
