Mineral-Coated Sand Soaks up Toxic Metals in Stormwater

The sustainably coated sand can remove organic pesticides and toxic metals including cadmium, copper, lead, and zinc.

Mineral-coated sand could unlock new water supply by removing two kinds of contamination.
Mineral-coated sand could unlock new water supply by removing two kinds of contamination.
UC Berkeley

A mineral-coated sand developed by engineers from the University of California Berkeley College of Engineering can soak up toxic metals like copper, zinc, lead, and cadmium in water and has the ability to destroy organic pollutants like bisphenol A. This material could assist communities and municipalities in improving stormwater quality. The team’s findings were published recently in the journal Environmental Science: Water Research & Technology.

Researchers already knew that the naturally occurring minerals they coated the sand with could react with organic contaminants like pesticides in stormwater, but the ability of the sand to also remove harmful metals could mean many more uses for urban stormwater runoff. In cities, stormwater runoff often picks up pesticides from lawns, lead from decades of leaded gasoline emissions, and other harmful pollutants that are associated with slowed neurological development in children and some types of cancer. However, researchers say their coated sand material could be installed in infiltration systems like rain gardens or even some parking lots. They estimate that this material could remove toxic metals from stormwater for over a decade in a typical infiltration system, which could then convey the runoff into underground aquifers.

"The pollutants that hold back the potential of this water source rarely come one at a time," said study lead author Joe Charbonnet, who conducted this research as a graduate student in civil and environmental engineering. "It makes sense that we fight back with a treatment technology that has these impressive double abilities to take out both toxic metals and organics. We suspected that the mineral-coated sand was special, but the way it continues to impress us with multiple capabilities is rather extraordinary." 

The researchers believe the material could turn urban runoff into a solution for strained water supplies, particularly in cities like Los Angeles that pay to import water. They suggest that Los Angeles and other cities with Mediterranean climates could store stormwater underground during wet winters and use it as a local supply during the dry season.  

“Rainwater used to percolate into the soil and recharge aquifers,” said David Sedlak, professor of civil and environmental engineering and co-author of the paper. “That changed when we covered city landscapes with hard surfaces like roads and buildings. As water-stressed cities try to figure out how to get urban stormwater back into the ground, we have serious concerns about the quality of that water. Our coated sands can remove not one, but two major classes of contaminants that threaten groundwater quality during stormwater infiltration.”

To make the filtration media, the scientists coated sand particles with manganese oxide, a naturally-occurring nontoxic mineral commonly found in soil. Work has already begun to investigate how well this material performs at large scales. Researchers have deployed large test columns of the mineral-coated sands to treat stormwater at sites in Los Angeles and Sonoma, CA.

This research was supported by the National Science Foundation (NSF) through the Engineering Research Center for Re-Inventing the Nation’s Water Infrastructure (ReNUWIt) and the NSF Graduate Research Fellowship.

Source: UC Berkeley

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