New technology developed by scientists at Stanford University and SLAC National Accelerator Laboratory could revolutionize how we disinfect drinking water. The low-cost, recyclable powder can kill thousands of waterborne bacteria per second when exposed to ordinary sunlight. The innovation has the potential to benefit nearly 30% of the global population that lacks access to safe drinking water. The results of the study have been published in Nature Water.
Conventional water-treatment technologies have long relied on chemicals and ultraviolet light, which have their drawbacks. Chemicals can produce toxic byproducts, while ultraviolet requires a source of electricity and takes a relatively long time to disinfect. The new disinfectant developed at Stanford is made up of a harmless metallic powder that absorbs both UV and high-energy visible light from the sun.
The powder consists of nano-size flakes of aluminum oxide, molybdenum sulfide, copper, and iron oxide. After absorbing photons from the sun, the molybdenum sulfide/copper catalyst performs like a semiconductor/metal junction, freeing electrons and reacting with surrounding water, generating hydrogen peroxide and hydroxyl radicals. These then kill the bacteria by damaging their cell membranes. The powdery nanoflakes can move quickly, making physical contact with a lot of bacteria and killing them rapidly.
The chemical byproducts generated by the sunlight also dissipate quickly. In fact, “if they don’t immediately find bacteria to oxidize, the chemicals break down into water and oxygen and are discarded within seconds. So you can drink the water right away.” said Yi Cui, the Fortinet Founders Professor of MSE.
Moreover, the nontoxic powder is also recyclable. Iron oxide enables the nanoflakes to be removed from water with an ordinary magnet. The same powder can even be used up to thirty times to treat thirty different samples of contaminated water. The study tested the technology on a 200 milliliter [6.8 ounce] beaker of room-temperature water, contaminated with about 1 million E. coli bacteria per mL [.03 oz.]. Within 60 seconds no live bacteria was detected after stirring the powder into the contaminated water and carrying out the disinfection test on the Stanford campus in real sunlight.
The innovation has tremendous potential, from hikers and backpackers carrying a tiny amount of powder and a small magnet to wastewater treatment plants. Current wastewater treatment plants rely on UV lamps to disinfect treated water. During the day, they can now use visible sunlight, which would likely save energy and work much faster than UV. The nanoflakes are also low-cost making the technology accessible to more people worldwide.
• At least 2 billion people worldwide drink water contaminated with disease-causing microbes.
• Waterborne diseases are responsible for 2 million deaths annually, the majority in children under the age of 5.
• The U.S. Environmental Protection Agency sets a maximum contaminant-level goal for E. coli in drinking water at zero.
Scientists at Stanford University and SLAC National Accelerator Laboratory have developed a low-cost, recyclable powder that can kill thousands of waterborne bacteria in seconds when exposed to ordinary sunlight. Iron oxide enables the nanoflakes to be removed from water with an ordinary magnet, making it a powerful solution to disinfect drinking water safely.
The innovation holds tremendous promise for people worldwide to gain access to safe drinking water. We hope to see this technology expand and scale up, helping people who currently lack access to clean drinking water. It’s heartening to see the innovation and creativity we can use to tackle some of the largest public health issues facing the world today.