Driving green desalination

Tapping Arizona’s natural power to produce clean water

Wilderness survival TV show hosts, pirates and water treatment researchers agree on one thing: most natural water sources are not safe for drinking.

Among the many potential risks is the high salt content of most inland water and seawater, which dehydrates the human body.

Desalination is the process of removing salt from water to make it drinkable. This process could create opportunities for enhancing water security, but its high costs and sustainability challenges are limiting its broader application.

In regions like Arizona, where natural water resources are scarce, innovative water conservation strategies are essential. These communities are committed to managing limited water resources responsibly by pushing to achieve zero liquid discharge, a goal that aims for nearly all water to be recovered during the water treatment process, with the contaminants reduced to solids, some of which can be reused for other purposes.

Tiezheng Tong, an associate professor of environmental engineering in the School of Sustainable Engineering and the Built Environment, part of the Ira A. Fulton Schools of Engineering at Arizona State University, is developing sustainable and cost-effective technology to support inland desalination for climate-adaptive water management.

Tong is one of a handful of researchers who received more than $1.2 million in support through the National Science Foundation’s Environmental Convergence Opportunities in Chemical, Bioengineering, Environmental and Transport Systems funding opportunity, which encourages scholars to tackle grand challenges as defined by the National Academies of Sciences, Engineering, and Medicine.

Solving water scarcity

Current methods for desalinating naturally occurring water, or brackish water, are costly and consume large amounts of energy. These processes also produce salty brine as a byproduct, with no environmentally friendly disposal options.

“Brackish water desalination is very much needed in water-conscious, inland cities like Phoenix,” Tong says. “We need to be able to use the resources available to us, such as the local brackish water and the sun.”

The team at Tong’s lab are seeking to adapt existing desalination methods to establish Arizona’s brackish water as a prospective alternate water source.

“Our initiative focuses on brine management and energy efficiency by incorporating procedures to achieve zero liquid discharge to maximize the yield of safe water while converting the brine into solid salts, which are much easier to manage,” he says.

The method challenges the limits of reverse osmosis by combining “salt-leaky” nanofiltration with reverse osmosis to achieve a higher water recovery and a reduced volume of brines.

The researchers will then couple a high-efficiency heat pump with a redesigned fiber-based crystallizer to provide an economically viable approach toward zero liquid discharge while reducing the carbon footprint.

As for the energy required to achieve zero liquid discharge, Tong is turning to Arizona’s most prolific and dependable resource: the sun.

He notes that achieving zero liquid discharge is still an energy-intensive process, but relying on Arizona’s most reliable renewable energy supply undercuts sustainability concerns and advances a zero-carbon footprint.

“We are looking for a comprehensive solution,” Tong says. “In every step of the process, for each industry facet, for the foreseeable future. The industry needs a multidisciplinary solution.”

A network to build the framework

From public perception to environmental impact, the team is discovering how to make inland desalination cheaper and more useful for the community at every step in the process. The comprehensive evaluation required Tong to establish an extensive network of multidisciplinary collaborators.

“Tackling so many different aspects of the process required an ambitious team structure,” Tong says. “By collaborating with experts in social sciences, renewable energy, economics and environmental life cycle analysis, we can achieve zero liquid discharge in a way that will provide meaningful results and minimize any potentially harmful environmental impacts.”

Shihong Lin, an associate professor of civil and environmental engineering at Vanderbilt University and one of Tong’s collaborators, says the project’s potential impact is hard to understate.

“I feel excited to have this opportunity to work on addressing the Achilles heel of inland brackish water desalination, which has the potential to play a major role in addressing the freshwater resource challenges due to the shifting climate,” Lin says. “Multidisciplinary collaboration is critical to maximizing the impacts of technological innovation and making sure we are seeking the right solutions that benefit the relevant community.”

Community focus and impact

The ultimate goals for the water treatment industry are zero-liquid waste desalination and a zero-carbon footprint. Tong’s methodology and thorough evaluation process offer a promising framework for brackish water desalination, a solution many believe to be the future of sustainable water security.

“Our target goal is ambitious,” Tong acknowledges, “but entirely possible.”

He says he is in the perfect location to tackle this challenge, viewing the grant as a vote of confidence from colleagues in his field in his ability to lead the project.

“I came to ASU for its history of leading large, impactful projects and to learn from this culture of leading multidisciplinary researchers,” Tong says. “It’s an honor to have the opportunity to lead such a large and talented team as a junior faculty member.”

The project is supporting the local community by creating research opportunities for ASU students from various academic backgrounds.

“We are always thinking about the next generation of engineers,” Tong says. “As the project gets underway, we will be recruiting students from various backgrounds and disciplines who will contribute to the expertise and inclusive excellence of the future workforce.”

Fulton Schools researcher Tiezheng Tong (right) and graduate research associates Shinyun Park (left), Yiqun Yao (center left), Xijia Ge (center) and Yuqi Wang (center right) are developing a sustainable and cost-effective approach to desalination. Photographer: Erika Gronek/ASU

Yiqun Yao, a civil, environmental and sustainable engineering doctoral candidate in Tong’s lab, says the project has been a great opportunity to cultivate her critical thinking and research skills.

“Dr. Tong’s hardworking and knowledgeable nature inspires us and shapes the type of researchers we aspire to become in the future,” Yao says. “I am truly excited about this opportunity to explore a field I haven’t had the chance to delve into before while also helping junior students discover their research passions.”

With a shared commitment to impactful research, Tong says he and his team are driven to advance solutions for critical water challenges.

“I’m confident that we can do great research that will develop technology with broad impact and help Arizona be more water sustainable.”