New solar technology can produce drinking water in large quantities is expected to reach millions of poor people

This solar distiller can produce record fresh water. Image source: UT AUSTIN

The tank equipment called "Solar Distiller" can use sunlight to evaporate dirty or salt water and condense the steam into safe drinking water. But a large and expensive distiller can only provide enough water for a small family. Today, researchers have developed a new material that can speed up the evaporation process so that small solar distillers can provide all the drinking water a family needs. If this technology proves to be cheap enough, it will provide clean drinking water to millions of poor people.

According to UNICEF data, there are currently 783 million people in the world, that is, nearly 1/10 of the population cannot access this service. These people spend a total of 200 million hours a day to fetch water from distant water sources. Although technologies for purifying sewage and desalinating seawater are currently available, these technologies usually require expensive infrastructure and large amounts of energy, which is unbearable for many communities.

Recently, researchers have been working to upgrade solar stills to a cheap, low-tech alternative. A traditional still is just a black-bottomed container filled with water, with a transparent glass or plastic lid on top. The black bottom absorbs sunlight, heats the water, evaporates it, and leaves contaminants. The water vapor then condenses on the transparent cover and eventually enters a collector slowly.

However, because sunlight must heat the entire volume of water before evaporation begins, the output of water is very low. The commercially available version produces about 0.3 liters of water per hour per square meter of covered area (L / h / m2). A person needs about 3 liters of drinking water every day. It takes about 5 square meters to provide enough drinking water for a small family. Theoretically, under the best operating condition of this device, it can only produce 1.6 L / h / m2.

Guihua Yu, a materials scientist at the University of Texas at Austin, and his colleagues recently reported a new way to get around this limit. It includes a hydrogel and a polymer mixture that forms a three-dimensional porous water-absorbing network.

Yu and colleagues used two polymers—a water-binding polymer called polyvinyl alcohol (PVA) and another light absorber called polypyrrole (PPy) —to make a gel-like sponge. Then put them on the water surface of a solar still.

Inside the gel, a layer of water molecules is tightly bound to PVA, and each layer of water molecules forms multiple chemical bonds, called hydrogen bonds. But because most of their bonding ability is related to PVA, the bound water molecules can only loosely combine with other nearby water molecules, and ultimately form what Yu calls "intermediate water."

Because there are fewer chemical bonds between the middle water molecules and the adjacent water molecules, they evaporate more easily than ordinary water. In this case, they are immediately replaced by other water molecules in the distiller.

Using this technique, Yu's solar still can produce 3.2 L / h / m2 of water, which is twice the theoretical limit. Yu's team reported this research result in the journal Nature-Nano Technology last year.

Today, Yu and his colleagues have developed a better hydrogel. This hydrogel is mixed with a third polymer, chitosan, which can absorb water strongly. Adding chitosan to the mixture can form a gel that can hold more water, thereby increasing the amount of intermediate water.

Researchers reported in the "Science Progress" magazine on June 28 that the solar distiller using this new hydrogel distilled water can work at a speed of 3.6 L / h / m2, which is the highest speed reported so far, which is about At present, it is 12 times of similar products on the market.

"This is an excellent starting point," said Peng Wang, an environmental engineer at King Tuwar Abdullah University of Science and Technology in Saudi Arabia. Wang pointed out that at such a high water production rate, a 1 square meter solar still can produce about 30 liters of clean drinking water per day, enough for a small family.

He said that even better, all three polymers in the hydrogel are commercially available and cheap. This means that if the distillers using these polymers are strong enough, they can provide clean drinking water for those most in need. (Zhao Xixi)

High Wattage Lamp Emergency Conversion Kit

Replacing Emergency Lights,Best Emergency Light,Automatic Emergency Light,Lamp Emergency Conversion Kit,led battery driver

Foshan Nai An Lighting Electric Co.,ltd , https://www.emballast.com