Two billion people worldwide lack safe water. Could a simple water-purification technique discovered at Stanford provide a solution?
According to a recent United Nations report, some two billion people lack access to safe drinking water. There are ways to address the situation — for example, through extensive filtration, treating the water with bacteria-killing chemicals, or exposing it to ultraviolet light. Unfortunately, filtration doesn’t always remove all contaminants, and chemical treatment often leaves toxic by-products in the water or affects its taste. The ultraviolet light method takes a long time to work and requires electricity that may not be readily available in remote areas.
But a team of scientists at Stanford University recently discovered a simple water purification technique that sidesteps the shortcomings of the other commonly used methods. It involves the use of a special powder that, when mixed into contaminated water and exposed to sunlight, reacts with the sunlight and instantly kills all waterborne bacteria. Only a tiny amount of the powder is needed, and the procedure takes just a few seconds.
The powder consists of harmless nanoflakes of aluminum oxide, molybdenum sulfide, copper, and iron oxide. The scientists say that when stirred into a beaker of bacteria-filled water, the powder absorbs photons from the sun and releases electrons that react with the water to produce hydrogen peroxide and hydroxyl radicals that quickly damage the cell membranes of bacteria and kill the bacteria. The chemical by-products dissipate within seconds and leave behind perfectly drinkable water. The iron oxide particles (which are chemically bonded to the other ingredients in the powder) can be collected using a magnet, so the powder can be reused indefinitely.
The scientists tested the powder in the lab in a 200 ml beaker of water contaminated with E. coli, a bacteria found in the human bowel that, if consumed in drinking water, can cause diarrhea, urinary tract infections, and even seizures or life-threatening kidney failure. All the E. coli were killed within a minute.
The senior author of the water-purification research paper, Yi Cui, Fortinet Founders Professor of Materials Science and Engineering (MSE) and of Energy Science & Engineering at the Stanford Doerr School of Sustainability, says the new technique has a variety of potential applications — in municipal water treatment plants where ultraviolet light is currently used to disinfect treated water, for example, or by backpackers who need a quick and easy way to get fresh drinking water when they’re on the trail.
“We believe that our novel technology will facilitate revolutionary changes in water disinfection and inspire more innovations in this exciting interdisciplinary field,” says Tong Wu, a former postdoctoral MSE scholar at the Stanford School of Engineering and a co-author of the paper.
The next step, the researchers say, is to test the treatment method on other viruses and organisms that contaminate water and endanger human health.
