Solar Filtration System Repurposes Greywater

NSF-funded collaboration between engineers and architects uses nanotechnology to combat water scarcity.

Prototype of the solar panel filtration system. (Image courtesy of Stanford.)

Prototype of the solar filtration system. (Image courtesy of UC Berkeley.)

Water scarcity is a growing problem in many parts of the world, but in the USA, the average family use several hundred gallons of water per day. Much of this becomes greywater, the runoff from sinks, baths and laundry that is dirtied by using it for washing.

In a new approach to water recycling, a group of architects and engineers at UC Berkeley are working on a device that collects greywater from a building throughout the day and cleans it—not to the point of being drinkable, but enough to use it again for washing or flushing toilets. As an added bonus, it can also be used for solar heating.

The device is a combination filtration system and solar array that can be mounted on the side of a building. Its design relies on a process called photocatalytic disinfection. Inside the solar panels, rounded glass surfaces are coated with gold nanoparticles that chemically react to UV light from the sun. The reaction process generates molecules that kill microbes, making the water safe for reuse. The heated water can also be recirculated through floor heating systems to warm the building.

UC Berkeley architect Maria Paz Gutierrez is collaborating with environmental engineer Slav Hermanowicz and bioengineer Luke Lee to build and test prototypes and determine how best to configure their setup.

The team hopes that this technology will be ready for commercial production within the next decade and that it will make a significant difference in parts of the world where water is in short supply.

“Using water only once is the norm in pretty much all of the developed world,” Slav said. “We want to use it at least twice. In this way we can cut the water demand, use solar energy—which is free—and we can also potentially capture that energy for other usage.”

Paz Gutierrez noted that end users benefit greatly, since they are using less water, electricity and gas (and therefore paying less for all three). 

But she also added that, “the city will benefit because it has less water to treat. The environment will benefit, because we’re not going to be contaminating aquifers…This is the future of sustainable building systems—synergistic optimization processes that are win-win from the local to the global scales.”

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