The punishing heat of a Mojave Desert summer has descended upon Southern Nevada. And though the long-term availability of the region’s water supply is a year-round question that lives quietly in the background, temperatures of 114 degrees or more bring those concerns right to the surface. 

A UNLV research team is working on a solution to ensure that none of our water ever truly goes to waste.

This spring, civil and environmental engineering professor Eakalak Khan received over $650,000 in phase II funding from the Cyrus Tang Foundation to continue a collaborative research project with a Chinese university partner, Northwest A&F University, exploring solar-powered wastewater reuse systems for rural households. The interdisciplinary team is wrapping up testing on the lab-scale unit on the UNLV campus and will proceed to onsite pilot testing in mid-fall.

“We're taking something that people don't want — wastewater — and making it into something they want,” said Khan. “It used to be labeled as waste or something that needs to be discarded. People think it’s yucky, right? Now, we’re trying to change that mindset so that it's viewed as a resource. It’s usable, or reusable.”

At the center of their innovation is graywater — the water that comes from showers and kitchen sinks and contains many soap byproducts like dish and laundry detergents. And their focus is on systems to serve rural communities.

The team developed a lab-scale model that treats the graywater. It first undergoes gravity separation and then passes through five different naturally sourced and affordable media — including sand, woodchips, and biochar — to clean the water at the household level. The second step of the two-part system is a solar still, which is currently stationed on the roof of a campus building. It uses the desert sun’s powerful rays to purify the water through evaporation and condensation.

From Graywater to Clear Water

Holding up three test tubes in Khan’s third floor Advanced Engineering Building lab, UNLV postdoctoral researcher Thi My Hanh Le demonstrated the early success of the lab-scale model.

The vials display a subtle gradient of colors: from untreated graywater on the left, to slightly lighter filtered water in the middle, and ultimately to clear, purified water that looks like it came straight from your kitchen tap.

“The quality coming up is superb,” Khan said. “It's definitely drinkable, though our current focus remains on non-potable reuse to be safe.”

The lab unit is set up to filter four liters of graywater, but the household unit — to be deployed in the coming months with the buy-in of a community partner — will be scaled up to filter 100 liters of water.

The household unit is being developed by David Rouhani, research laboratory manager for the department of civil and environmental engineering and construction, and will employ a cassette system with drawers so that users can easily isolate the different media layers for cleaning or replacement.

“Initially we said we're going to put all five of them in layers into a single enclosure, but now we’re planning to separate them into multiple enclosures — a plug-and-play system if you will — to make it easier for rural households,” Khan said.

The Next Phase

Now that they're ready to move into onsite testing, there's one question they have to answer: Which community is open to a partnership?

Khan and his team have met with several communities in Southern Nevada and identified three potential community partners. But they know they need to work with the community to overcome public perception concerns over the safety of the treated wastewater before they begin installation. Project collaborators from Northwest A&F University in China are also scouting for rural communities in an arid region of the country that mirrors the climate of the Southwest U.S.

“Looking at all the water quality parameters, they are great,” Khan said, adding that he hopes the chosen community partner can take a page from San Diego.

“San Diego has a full-scale wastewater reuse plant almost completed,” he said. “It took many years for the project to be accepted but San Diego residents eventually realized, 'Hey, we either drink this, or we don’t have anything else to drink.’ We’d like to achieve a similar level of comfort here in Nevada."