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Engineered Sand Can Create Safe Reservoir of Drinking Water for Water-Stressed Communities

A novel method has been developed by UC Berkeley engineers to eliminate contaminants from storm water. This latest breakthrough could tackle the needs of parched communities looking for ways to tap the profuse but underused source of fresh drinking water.

Reclaimed storm water may provide a local source of drinking water for parched communities. (MPCA Photos, via Flickr)

When the researchers used a mineral-coated sand, which reacts with and damages organic pollutants, they found that storm water percolating into underground aquifers could be purified with this engineered sand to create a safe and local reservoir of drinking water for water-stressed communities.

The way we treat storm water, especially in California, is broken. We think of it as a pollutant, but we should be thinking about it as a solution. We have developed a technology that can remove contamination before we put it in our drinking water in a passive, low-cost, non-invasive way using naturally-occurring minerals.

Joseph Charbonnet, Graduate Student in Civil and Environmental Engineering at UC Berkeley

As rain water rushes over the streets, roofs, and lawns, it can gather a slew of unpleasant chemicals such as pesticides, herbicides, car oil, toxic metals, and even dog poop. Excess amounts of storm water can also flood basements and streets and overwhelm sewer systems. As a result, cities frequently discharge this polluted water into adjoining streams and rivers as swiftly as possible.

According to Charbonnet, one ideal solution would be to direct the storm water via sand into underground aquifers for collecting water in Mediterranean climate regions like Los Angeles. Aquifers are similar to giant rain barrels; they can be filled during periods of high rainfall and can store water until required in the dry season.

Storm water reclamation is already being used by cities on smaller scales through serveral constructs like rain gardens and bioswales, which direct storm water through mulch or sand to eliminate debris and prevent surface runoff.  Along with his adviser David Sedlak, Charbonnet is working with the local community in the Sun Valley neighborhood of Los Angeles to convert a 46-acre gravel pit into a wetland and water infiltration system for storing storm water.

Before we built the buildings, roads and parking lots that comprise our cities, rainwater would percolate into the ground and recharge groundwater aquifers. As utilities in water stressed regions try to figure out how to get urban storm water back into the ground, the issue of water quality has become a major concern. Our coated sands represent an inexpensive, new approach that can remove many of the contaminants that pose risks to groundwater systems where storm water is being infiltrated.

David Sedlak, Professor of Civil and Environmental Engineering at UC Berkeley and Co-Director of the Berkeley Water Center

While the coated sand is not capable of removing all types of contaminants, it can possibly be used along with other water purification systems to remove most of the contaminants that are picked up by water, said Sedlak.

The researchers have described their findings in the journal, Environmental Science & Technology.

Borrowing Chemistry from the Soil

In order to create the coated sand, Charbonnet mixed two forms of manganese, which react to produce manganese oxide, with plain sand. Manganese is a harmless mineral that adheres to organic chemicals such as the endocrine-disrupting bisphenol-A (BPA), pesticides, and herbicides and breaks them down into tinier pieces that are more biodegradable and usually less toxic.

Manganese oxides are something that soil scientists identified 30 or 40 years ago as having these really interesting properties, but we are one of the first groups to use it in engineered ways to help unlock this water source,” said Charbonnet.

Dull brown in color, the manganese oxide-coated sand is both safe and environmentally friendly. “I guarantee that you have some manganese oxide on your shoe right now because it is ubiquitous in the soil,” stated Charbonnet.

In order to test the sand, Charbonnet percolated simulated storm water that had a low concentration of BPA, via the material’s columns. Initially, while the coated sand was able to remove almost all of the BPA, it lost its effectiveness over time. Conversely, it is possible to recharge the manganese oxide by bathing the sand in a solution that contained a low concentration of chlorine. All the initial reactivity of the manganese oxide was restored by recharging the sand.

If you have to come in every year or two and dig up this sand and replace it, that is incredibly labor intensive, so in order to make this useful for community stakeholders it’s really important that this stuff can be regenerated in place.

Joseph Charbonnet, Graduate Student in Civil and Environmental Engineering at UC Berkeley

Charbonnet estimates that recharging a half-meter-deep layer of sand utilizing 25 parts per million of chlorine in water - the concentration used for treating wastewater - would take roughly two days.  In the next stage of the experiment, the researchers are conducting field tests in Sonoma County by utilizing storm water from a local creek.

The paper’s co-authors are Yanghua Duan from the Department of Civil and Environmental Engineering and Case M. van Genuchten from the Department of Earth Sciences, Geochemistry, and Faculty of Geosciences at Utrecht University.

The National Science Foundation Engineering Research Center for Reinventing the Nation’s Urban Water Infrastructure (ReNUWIt) and a National Science Foundation Graduate Research Fellowship supported the research.

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