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Jim Park with tires
February 26, 2020

Tired out: A surprising second purpose for a challenging source of waste

Written By: Alex Holloway

Nearly 1 billion tires are disposed of around the world every year.

UW-Madison engineer Jim Park hopes to give those non-biodegradable hunks of rubber new life, putting them to use to help clean our water.

A professor of civil and environmental engineering, Park has studied ways to use recycled tires for more than 20 years. Through his research, in collaboration with the First State Tire Recycling & R-TEA Manufacturing Company, Park has found that recycled tires can have significant uses in civil engineering applications and for helping to remove an array of harmful chemicals from runoff water.

Scrap tires can be shredded to create tire-derived aggregate (TDA), a spongy material that engineers can use in everything from stormwater treatment systems and underground water retention to foundations for roads or insulation. Applications where runoff passes through a TDA buffer can help remove heavy metals, organic compounds or phosphorus before they get into streams or lakes. For example, through his research, Park has found that an 8-inch-thick rubber tire layer could remove 90 percent or more of 37 different pesticides from water.

“Rubber is like a sponge,” he says. “It can absorb toxic chemicals, including heavy metals. We designed a method to determine the number of tires needed to remove target contaminants for a design period. That is typically 50 to 100 years, and with these applications we can help the environment.”

Phosphorus is a major water quality concern, especially for runoff from agricultural use. While phosphorus can be vital for crop growth, excess carried away from farms by rain or melting snow can get into lakes and streams. Too much phosphorus can lead to eutrophication. Eutrophication encourages toxic algal blooms, which can deplete oxygen in water and kill aquatic life. According to UW-Madison research, it could take eutrophic lakes hundreds of years to recover.

The steel wires embedded in some tires enhance phosphorus removal. Park says stormwater treatment systems filed with TDA can clear 60 to 80 percent of phosphorus present in runoff water. That presents a new use for recycled tires to aid in phosphorus removal, which can otherwise be a difficult process—especially for small-scale facilities.

“What we figured out was that you can create a buffer zone embedded with scrap tires containing a high amount of steel wire,” he says. “Before runoff can get to a body of water, it goes through the buffer zone, which helps remove phosphorus.”

Based in Isanti, Minnesota, First State Tire Recycling makes TDA for use in engineering projects and recycles more than 2 million tires per year. The recycled tires have gone to use in more than 350 construction projects over 30 years. CEO Monte Niemi says Park’s results have been invaluable for building confidence in using TDA as a filtering medium for a variety of civil engineering applications.

“The work that Professor Park is doing could be considered critical as far as the future of what we can do with these tires,” Niemi says. “If we don’t know what to do with them, they end up going to the landfill.”

Park says he hopes TDA will continue to gain traction as a material for engineering applications, whether that’s as a foundational material beneath construction projects, or as a filter for runoff drainage.

“This isn’t just research in a lab,” Park says. “This is something we want to have real-world impact. Through this innovative method, more people can upcycle scrap tires for beneficial use.”