Coated sand purifies storm water

Engineers have developed a way to purify storm water runoff that is usually wasted.

Many cities are beginning to experience shortages of water for at least part of the year. At the same time, most rainwater that falls in built-up areas just runs off the streets and down the sewer drains – rather than percolating into the ground to recharge groundwater aquifers. Herbicides, pesticides, toxic metals and car oil often also contaminate this storm water, making it difficult to reclaim. Now, researchers at UC Berkeley have developed a way to remove contaminants from storm water.

The researchers developed a mineral-coated sand that destroys organic pollutants. To create the sand, engineers mixed plain sand with manganese oxide. The manganese oxide binds to organic chemicals such as herbicides, pesticides, and bisphenol-A. These bonded chemicals then break them down into smaller molecules that are less toxic and more biodegradable. The manganese oxide-coated sand is safe and environmentally friendly.

Although the coated sand loses its effectiveness over time, researchers have found a way to ‘recharge’ it in place by bathing the sand in a solution containing a low concentration of chlorine. Joseph Charbonnet, a graduate engineering student working on the project, suggests that the decontaminated storm water pass through the sand and into underground aquifers. The aquifers would act as storage units for the water until there is need for it. In the next phase of the experiment, the team is performing field tests in Sonoma County using storm water from a local creek.

Finding new ways to save and recycle water is becoming more important. We have already seen other innovations in water recycling. These include toilets that can recycle water and low cost grey water recycling. According to Charbonnet, “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”.