Can the Sun Purify Water?

Researchers from the University of Buffalo in New York have struck upon a novel way to channel the power of the sun’s rays to purify water. Although using solar power to cleanse water is not in itself a new technique, the simple materials and ingenious method involved here make it markedly more efficient than previous methods.

Refining an old technique

Solar stills are a tried and tested method of purifying water. Harnessing the power of the sun to evaporate water, the method soaks up all water and turns it into vapour, leaving salt, bacteria, micropollutants and other contaminants behind. The vapour can then be cooled and converted back into H20, now free from pollutants.

“Most groups working on solar evaporation technologies are trying to develop advanced materials, such as metallic plasmonic and carbon-based nanomaterials,” explained Professor Qiaoqiang Gan, an associate professor and lead author on the paper. “We focused on using extremely low-cost materials and were still able to realise record-breaking performance.”

Low-cost, high-impact

Professor Qiaoqiang’s method hinges upon a sheet of paper dipped in a carbon solution and folded into an upside-down V shape, similar to a birdhouse rooftop. The lower parts of the paper rest in the water, soaking it up slowly like a napkin might, while the carbon coating is adept at magnifying the heat of the sun and using it to convert the water into vapour.

By folding the paper into the V shape, the researchers were able to keep it cooler and regulate the amount of sunlight which reaches it. This allows the majority of the paper to remain at room temperature, thus preventing the heat loss that normally occurs with such techniques. In this way, the team successfully evaporated 2.2 litres per square metre of carbon paper per hour. That’s a significant upgrade on the 1.68 litres previously thought to comprise the upper limit of solar still purification.

Helping where it’s needed most

With climate change posing an ever-greater threat and global populations escalating at an ever-faster rate, there is a need for all of us to become more water-efficient. Techniques like the one pioneered by Professor Qiaoqiang and his team could be instrumental in meeting the demands of today’s world, as it’s cheap, low-tech and utilises an eminently available power source in the sun.

Those behind the project have already set up a start-up company called Sunny Clean Water dedicated to bringing the idea to fruition and allowing it to be used by those who need it most. It’s projected that the technology can be used to produce between five and eight kilograms of water from a day enjoying eight hours of sunlight, which should be enough to sustain the needs of an entire family. Therefore, it’s an ideal option for the developing world where plentiful clean drinking water is hard to come by.