Hydrogel, Solar Power Provide Simple Water Purification

Dead Sea salt deposits — Salt deposits by the Dead Sea (Bader Mawasy, Public Domain Pictures)

4 April 2018. An engineering lab demonstrates how polymer gels and ambient sunlight can provide a simple, inexpensive alternative to current complex and expensive technologies for desalinating or purifying drinking water. A team from University of Texas in Austin describes its techniques in the 2 April issue of the journal Nature Nanotechnology (paid subscription required).

Populations using unsanitary water are a global problem, particularly in low-resource regions. World Health Organization estimates 844 million people lack even a basic service providing uncontaminated drinking water, either located on their premises or available when needed. Pathogens in drinking water contaminated with human or animal feces lead to diarrheal diseases, such as cholera, which according to Centers for Disease Control and Prevention, kill more children than AIDS, malaria, and measles combined. About 88 percent of those deaths, says CDC, can be traced to unsafe water, inadequate sanitation, and poor hygiene. Even in more advanced societies, municipal water systems can break down due to natural disasters, such as floods or hurricanes.

A team from the lab of UT-Austin mechanical engineering and materials science professor Guihua Yu are seeking simpler and more economical, yet still reliable solutions for water purification and desalination. Systems using evaporation for drinking water are in use today, but this technology, say the authors, relies on complex add-on equipment to concentrate solar energy for generate enough heat to separate clean water from salt or contaminants. As a result, few of these current systems are available for many of the places that need them.

The solution created by Yu and colleagues in Austin, as well as at University Colorado in Boulder and Beijing Institute of Technology in China, employs a hydrogel — a water-based polymer material — designed with a nanoscale polymer structure to harness and concentrate sunlight. The structure of common polymers polyvinyl alcohol and polypyrrole in the gel are constructed in a hierarchical mesh that not only captures direct sunlight, but also channels the raw, unpurified water through the system for evaporation and separation of contaminants. Water vapor is then condensed and purified water is pumped to a separate holding tank.

The following brief video demonstrates operation of the device …

Credit: Guihua Yu, University of Texas – AustinThe researchers tested a prototype device with contaminated water samples, including water from the Dead Sea bordering Israel and Jordan, with a salinity rate of 34 percent, 10 times the salinity of the Atlantic and Pacific oceans. The tests conducted outdoors show a square meter of the nanostructured hydrogels can produce up to 23 liters of purified water per day, enough for household needs as well as disaster areas.

The university says it applied for a patent on the technology and Yu’s lab is working with the campus technology transfer office to make the system available for commercialization.