Special sand could let us drink stormwater from the streets
When it rains heavily, even in arid places where water is scarce, the stormwater typically just runs off the streets and down the sewer drains. Thanks to a new "engineered sand," though, that road-polluted liquid could soon be cleaned up and used for drinking water.
Developed at the University of California Berkeley, the material is actually just regular sand that's been mixed with two types of naturally-occurring manganese. These react with one another to become manganese oxide, which is harmless to humans and the environment.
When water contaminated with organic pollutants such as herbicides, pesticides and bisphenol-A (BPA) is run through the sand, those chemicals bind with the manganese oxide. As a result, they're either removed from the water, or they're broken down into smaller pieces which are less toxic and more biodegradable – a secondary purification system, used in tandem with the sand, could then likely take care of them.
Although the effectiveness of the manganese oxide does diminish over time, it can be completely "recharged" by running weakly-chlorinated water through the sand. It is estimated that a half-meter-deep (1.6-ft) layer of the sand could be revitalized by running such water through it for about two days, at a chlorine concentration of 25 parts per million.
Ultimately, it is hoped that the sand could be placed over underground water-storing aquifers, with stormwater runoff percolating through the material before entering them. In the immediate future, though, the scientists plan on testing the technology on stormwater from a creek in Sonoma County.
"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," said grad student Joseph Charbonnet, a member of the research team. "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."
A paper on the study was recently published in the journal Environmental Science and Technology.