Nov 07, 2018

A Sandy Scarcity Solution

Water Quality Products managing editor interviews a researcher from University of California, Berkeley, regarding an engineered sand water filtration solution

Interview with researcher on engineered sand water filtration solution
Joe Charbonnet

With water scarcity plaguing many areas of the world, researchers are searching for ways to maximize the availability of freshwater.  Oftentimes, the solution is not found in nature.  A team of researchers at the University of California, Berkeley, has developed an engineered sand that can filter pollutants from storm water, thus creating the potential for a safe drinking water supply for water-scarce communities. WQP Managing Editor Amy McIntosh asked Joe Charbonnet, a member of the research team, about the project. 

Amy McIntosh: How did you develop the engineered sand, and what is it made of? 

Joe Charbonnet: The engineered geomedia is made of normal sand covered with a naturally occurring mineral called manganese oxide. We make the engineered geomedia by mixing two different kinds of manganese in the presence of sand, which react together to create the manganese oxide coating. 

We developed a way to make the engineered geomedia at room temperature and pressure, rather than [under] some of the more extreme conditions that have been used for making manganese oxide in previous scientific research.

McIntosh: How does the sand remove pollutants from water?

Charbonnet: The manganese oxide in the geomedia reacts with certain types of organic compounds, including contaminants like bisphenol A, turning them into less toxic and more biodegradable chemicals. Over time, however, the reactivity of the engineered geomedia drops off. 

We figured out a way to regenerate the reactivity of the manganese oxide-coated sand without having to dig it up. This regeneration technique, using the same form of chlorine found in swimming pools, could make this technology easy to use and affordable for cities.

McIntosh: How can it treat storm water runoff? 

Charbonnet: This engineered geomedia would fit into infiltration systems just like normal sand, but use cutting-edge chemistry to remove contaminants. While small-scale infiltration systems like rain gardens are so familiar that we walk past them without a second look, this technology could help to facilitate the construction of larger infiltration systems. These systems, which could look like parks and be up to several acres in size, could collect substantial amounts of water and help to replenish cities’ underground drinking water supplies.

McIntosh: How could the sand benefit water-scarce communities?

Charbonnet: Many cities, especially in the western U.S., spend enormous amounts of energy and money to import water over long distances. At the same time, cities have often viewed storm water as something to get rid of as quickly as possible before it creates flooding. But with urban populations growing and prolonged droughts becoming more common, freshwater literally falling from the sky starts to look pretty darn good. But there’s a problem: In addition to storm water, our gutters contain automotive exhaust, tire wear products, and pesticides from our yards. We’d like to keep these contaminants out of our drinking water supply. Manganese oxide-coated sand can help cities turn what was pollution into a low-cost, local water solution.

McIntosh: What is next for you and your research team? 

Charbonnet: There is evidence that in addition to its reactivity with organic compounds, manganese oxide-coated sand could also be very effective for removing toxic metals like lead from storm water. So we’re now researching whether this engineered geomedia can deliver a one-two punch to both organic and metallic contaminants in storm water. We are also conducting field-scale studies with industry partners to determine how well manganese oxide-coated sand performs alongside other useful geomedia like charcoal.

About the author

Joe Charbonnet is a doctoral student in environmental engineering at the University of California, Berkeley. Charbonnet can be reached at [email protected]

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