by Adele Peters: Leave it in a bottle and it uses the water’s own oxygen to destroy bacteria…
After sitting in the sun, a piece of coated plastic can turn sewage water into clean drinking water at almost no cost.
A photocatalytic material (which uses light to fuel a chemical reaction) designed by researchers at the University of Edinburgh absorbs sunlight, generating high-energy electrons that activate oxygen in the water, destroying organic compounds like bacteria. The material can easily be added to plastic to create a cheap water purifier.
“It’s just channeling the sunlight towards the destruction of all these pollutants and bacteria,” says Neil Robertson, the chemistry professor leading the research.
The materials are fully solar-powered, so they don’t require an outside energy source. Unlike some other water purification systems, there are no moving parts to break. And the system is incredibly cheap to make.
“What we’re aiming for is simplicity,” says Robertson. “The 750 million people in the world who have no access to improved water are often living in fairly poverty-stricken conditions and don’t have access to the money to buy complex systems.”
In its simplest form, a transparent plastic sheet coated with the photocatalytic material could be rolled up inside a plastic bottle, and the bottle could be filled with contaminated water. After the bottle sits in the sun, the water will become safe to drink.
The material could also be used in combination with a filter to remove larger particles, but in water that’s primarily filled with dissolved pollutants, a filter wouldn’t be necessary.
Because the plastic and photocatalytic material are both cheap to manufacture, when the finished product makes it to market, it would also be very low-cost.
“The actual embedded cost in the materials themselves is absolutely negligible,” says Robertson. “The cost left, then, would simply be those associated with production and distribution.”
Because the photocatalytic material is also simple to manufacture, the researchers envision that it could be produced locally.
Ultimately, the material could also be used to treat sewage water at an earlier stage; in rural areas in the developing world, wastewater often isn’t treated and ends up polluting drinking water.
“A more attractive, or longer-term solution is to purify water before it runs to ground, but that requires more thought on infrastructure and also the social science of the choices people make,” Robertson says. “From a social science perspective, there’s probably less of an immediate personal benefit to treating water you’re disposing of rather than water you’re about to drink . . . it’s a harder challenge.”
In a pilot project in India, the team fabricated the material and tested it in the lab, and will soon begin running tests in villages.