Artificial sand solving real problems

A team of engineers, hailing from UC Berkeley, has developed a mineral-coated sand that can soak up toxic metals, like lead and cadmium from water. Paired with its ability to destroy even organic pollutants (like bisphenol A), this material could be able to help cities tap into stormwater—an abundant, but highly underused water source.

These researchers were aware that the naturally occurring minerals they coated onto the sand could react with organic contaminants in the stormwater. However, the ability of the coated sand to also remove harmful metals during filtration, could unlock vast possibilities regarding the polluted drain water.

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Cities with Mediterranean climates, like Los Angeles, could store stormwater underground during their wet winters, and it could serve as an inexpensive, local water supply during the long dry season. But this resource has gone mostly untapped because stormwater characteristic to pick up toxic chemicals as it runs through streets and gutters of the city. Exposure to these chemicals is associated with slow neurological development in children and some types of cancer.

“The pollutants that hold back the potential of this water source rarely come one at a time. 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.”

Study lead author Joe Charbonnet
Image source: Photo by Jake Nackos on Unsplash

However, researchers say that their coated sand material could be installed in rain gardens in places like parking lots where stormwater can be collected and cleaned. They estimate that this material could remove metals from stormwater for over a decade in a typical infiltration system, which would convey runoff into underground aquifers. The researchers see this material turning pollution into a solution for strained water supplies, particularly in parched cities that pay to import water.

“Rainwater used to percolate into the soil and recharge aquifers. 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.”

David Sedlak, professor of civil and environmental engineering and co-author of the paper

To make the filtration media, the scientists coated sand particles with manganese oxide, a naturally-occurring nontoxic mineral commonly found in soil all over the world. Research 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, California.

Sourced from UC Berkeley Engineering