Water

When David Warsinger talks about water, it’s never just about water.

It’s about thermodynamics, membranes, microbes, minerals, agriculture, geopolitics — and the quiet urgency of building systems that actually work in the real world.

Now a faculty member at Purdue University, David’s path to leading one of NAWI’s most ambitious desalination pilot projects began years earlier in an MIT conference room, crowded around a whiteboard with . What started as a “side project” during his PhD has since evolved into patented technology, multiple partnerships with startups, international research momentum — and, most recently, NAWI support to build the largest true-batch seawater reverse osmosis (RO) system ever developed.

Rethinking Desalination at Its Core

Conventional reverse osmosis desalination operates continuously: water flows in, pressure stays high, and energy is often wasted by overpressurizing the system. David and his collaborators questioned a foundational assumption — what if desalination didn’t have to be continuous at all?

Instead, they explored batch and semi-batch reverse osmosis, where pressure changes dynamically over time to closely follow the minimum pressure required to desalinate water. This subtle shift turns out to matter a lot.

But there was a catch. A true batch system requires precise, simultaneous control of both pressure and volume — something that hadn’t been solved before at scale. Through persistent whiteboard brainstorming and years of iteration, David and cracked the problem, leading to patented configurations that laid the groundwork for today’s pilot systems.

NAWI Support Enables a First-of-Its-Kind Pilot

With support from NAWI, David’s team at Purdue, Colorado School of Mines, and Oak Ridge National Lab set out to do something bold: build the largest true-batch RO pilot system in the world.

Housed on a 25-foot trailer and operating up to 40–50 gallons per minute , the system is anything but small. The membrane vessels are roughly 10 feet long, the valves are “about the size of a person’s head,” and the main pump and motor weigh nearly 180  pounds. What began as a proposal for a 10-gallon-per-minute system grew — with NAWI’s encouragement and additional resources from collaborator Tzahi Cath’s Department of Defense project — into a five-times-larger, fully modular pilot platform.

The system is designed to compare multiple desalination modes side-by-side: continuous RO, semi-batch RO, true batch RO, and other emerging configurations. It can test seawater, brackish water, high-salinity brines, and even difficult industrial and agricultural wastewaters — making it a flexible testbed for next-generation water treatment.

Beyond Energy: Scaling, and Recovery

Energy efficiency is only part of the story.

Because batch RO cycles salinity up and down every few minutes, it naturally disrupts biofilm formation, a major cause of membrane failure in conventional systems. The rapid salinity changes can cause microbial cells to swell and burst — a phenomenon David’s team has been studying in detail.

Batch operation also opens the door to higher water recovery. Traditional desalination systems avoid operating near salt saturation to prevent scaling and crystallization, which can permanently foul membranes. But batch RO can safely pass through supersaturated conditions for short periods, allowing operators to extract more water from the same feed — an especially valuable advantage for brines, groundwater, and mineral-rich streams.

Applications: Who Benefits First?

While municipal utilities tend to be slow adopters of new technology, David sees near-term impact in industry — particularly sectors that already handle difficult waters.

Critical minerals like lithium and iodine often come from salty brines that are currently concentrated using massive evaporation ponds. Batch RO could dramatically reduce land use, energy demand, and environmental impact in these processes. Agricultural wastewater, industrial reuse, and high-recovery treatment for PFAS and other emerging contaminants are also strong candidates.

Some of this impact is already happening. Variations of David’s batch-inspired designs have been adopted by startups treating animal wastewaters and agricultural flows — with systems now operating at over one million gallons per day.

Scaling Science in a Challenging Funding Landscape

Building hardware-intensive systems on accelerated timelines isn’t easy — especially in today’s uncertain research funding environment. David is candid about the challenges: short pilot timelines, the difficulty of sustaining graduate student support, and the broader consequences of delayed or canceled federal funding.

Yet the urgency only reinforces the stakes.

Water security, critical minerals, agricultural resilience, and energy efficiency are deeply interconnected. Technologies that improve desalination efficiency and recovery don’t just make water cheaper — they help secure food systems, reduce geopolitical vulnerabilities, and protect ecosystems from salinization.

Training the Next Generation

Beyond the technology itself, David is deeply invested in people. His lab has trained an unusually large number of graduate students for an early-career faculty member, many of whom have gone on to faculty roles, startups, and leadership positions in water research.

He also leads outreach efforts with K–12 students, coaches intercollegiate water and marine energy teams, and believes strongly that early exposure to water science shapes future careers.

“If people understand water early,” he says, “they care about it differently.”

Looking Ahead

With NAWI’s support, David’s team is pushing batch reverse osmosis beyond proof-of-concept toward commercialization-ready scale. The goal is simple — and ambitious:

To make desalination and water reuse less energy-intensive, more resilient, and more capable of handling the waters we can no longer afford to ignore.

What began as a whiteboard exercise is now rolling on a trailer, valves humming, membranes cycling — quietly redefining what’s possible in water treatment.

The National Alliance for Water Innovation (NAWI) NextGen Program supports the development of early-career NAWI researchers and members of the alliance to help build a domestic workforce capable of driving future research and development in the water energy sector. Early-career NAWI-affiliated scientists, including graduate students, postdoctoral researchers, and early-career staff members are encouraged to join the program!

Exploring how tiny chemical structures can tackle big environmental challenges, from PFAS contamination to resource recovery.

What makes a material truly effective—and how can those insights spark the next generation of solutions? That’s the question NAWI researcher Ethan Pezoulas and his team are answering by moving beyond material design to uncover the principles that drive performance.

For Ethan, an interest in water started long before graduate school—shaped by years spent outdoors in Alberta, Canada. “I grew up hiking, camping, skiing, and playing hockey,” he says. “I was surrounded by rivers, lakes, and snow-fed streams. You can’t spend that much time outdoors and not start thinking about how vital water is—and how we manage it.”

After earning his BSc in Chemistry from the University of Calgary, Ethan moved to Berkeley to join the Jeff Long research group at UC Berkeley. Now in his fifth year of a  Chemistry PhD program, he reflects: “I’ve been loving it.” His academic path was driven by curiosity and a desire to bridge two worlds—fundamental chemistry and real-world impact. “I like knowing the fundamental chemistry, but what’s most satisfying is applying it to real-world problems,” he says.

That mindset defines Ethan’s work today. “The overarching theme of my research is developing porous materials for aqueous separations of environmental and economic importance,” he explains. In simple terms, Ethan creates tiny structures with chemical ‘hooks’ that latch onto specific substances. He then builds these into porous materials—like advanced sponges—that can pull certain contaminants out of water while letting everything else pass through.

Within his NAWI project, Ethan is tackling two major challenges: removing selenium and PFAS from water. PFAS—often called “forever chemicals”—are persistent, harmful substances found in nearly every water source on the planet. Selenium, while essential in trace amounts, can be toxic at higher concentrations and is a growing concern in wastewater from agriculture and industry.

Ethan’s materials work by selectively binding these contaminants, pulling them from water while leaving behind what’s safe. And here’s the breakthrough: by studying why these chemical modifications work so well, Ethan and his team discovered design principles that can be applied beyond their current system.

“In theory, you could take what we learned about the chemical modifications and apply it to different frameworks or different sponges that might be better suited for other applications,” Ethan explains.

That insight turns a single innovation into a platform for many—enabling next-generation adsorbents that could address a wide range of water challenges.

For Ethan, this isn’t just academic achievement; it’s part of a bigger vision. “I want to keep doing research for direct application—taking what we know and applying it to real-world solutions,” he says. While he values fundamental science, his passion lies in innovation that makes a difference. “It’s satisfying to know the principles behind something, but the real excitement comes when you can see it making an impact.”

The National Alliance for Water Innovation (NAWI) played a pivotal role in this journey. Beyond funding, NAWI provided clarity on priorities, access to resources, and a network of collaborators. “NAWI gave us direction and connected us with a community. Those conversations and partnerships have been just as important as the research itself,” Ethan notes.

Outside of NAWI, Ethan is exploring how to recover critical minerals—such as precious metals or rare earth elements—from the chemical solutions left over after recycling electronics, magnets, and batteries. “Instead of mining raw materials, which can be environmentally destructive, we can recover critical elements from existing waste streams,” he says. This not only supports sustainability but also strengthens supply chains for clean energy technologies.

As he looks ahead, Ethan is leaning toward industry—where fundamental research can become products that change how water is treated worldwide. His work is a reminder that understanding the science behind performance isn’t just academic—it’s the key to unlocking cleaner, safer, and more sustainable water technologies for the future.

The National Alliance for Water Innovation (NAWI) NextGen Program supports the development of early-career NAWI researchers and members of the alliance to help build a domestic workforce capable of driving future research and development in the water energy sector. Early-career NAWI-affiliated scientists, including graduate students, postdoctoral researchers, and early-career staff members are encouraged to join the program!

Hannah Holmes’s journey from a small town in southern Illinois to the research labs at Stanford University was driven by curiosity and a passion for making science meaningful, especially for communities like the one where she grew up.

Raised in a town of just 4,000 residents, she had little early exposure to science. That changed in high school when a chemistry class sparked her curiosity. Her interest grew after shadowing a female chemical engineer at the oil refinery where her father worked. Inspired by the field’s use of science and math to solve real-world problems, she went on to study chemical engineering at the University of Illinois Urbana-Champaign.

Hannah’s academic path has spanned several scientific areas, all of which have focused on pollutant removal and reuse. At the University of Illinois, she worked on electrochemical processes that transform carbon dioxide into fuels and chemicals. During her Ph.D. studies at Georgia Tech, her research centered on carbon capture from air or flue gas. After a post-seminar conversation with Stanford’s Will Tarpeh, she shifted her focus to water-based separations, leading to her current role as a postdoctoral researcher in his lab.

At Stanford, she is developing electrochemical processes to recover nutrients from wastewater. Her work involves building low-impact systems to recover critical nutrients like phosphate, an essential component of agricultural fertilizers. After fertilizer application, excess nutrients carried by irrigation or rainfall to lakes and reservoirs can cause large algae blooms, which harm both the environment and human health. A key project uses a hybrid electrochemical ion exchange process to recover phosphate as fertilizer through electrochemical regeneration, a lower-carbon, more cost-effective alternative to conventional chemical methods. She explains, “By recovering phosphate as fertilizer, we can close the loop and transform pollutants back into valuable products.”

What sets her research apart is its multi-scale approach. One day she might analyze molecular-level adsorption mechanisms with synchrotron tools; the next, evaluate broader impacts through technoeconomic and life cycle analysis. This range allows her to approach each challenge from both molecular and systems-level perspectives. She notes that while adsorbent and electrochemical processes have been scaled independently, integrating them shows great promise. “There’s a path forward for integrated systems,” she says.

Her interest in environmental technologies is rooted in a pivotal undergraduate lecture on the disproportionate effects of climate change on rural areas. “I wanted to use my chemical engineering background to help places like my hometown,” she recalls.

Looking ahead, Hannah hopes to expand her work to other pollutants—both gaseous and aqueous—and envisions “refineries of the future” that turn waste into valuable products using scalable, energy-efficient technologies. But she acknowledges that technical innovation alone is not enough. “We still need buy-in from funders and treatment facilities,” she says, citing the inertia and limited incentives that can slow real-world adoption.

Although her work is highly technical, Hannah emphasizes the human side of science. She values in-person interactions—especially at conferences—for building authentic, lasting relationships. As a member of the National Alliance for Water Innovation (NAWI) NextGen Leadership Committee, Hannah recently helped lead a mixer during the NAWI quarterly review meeting to encourage interaction and collaboration among graduate students, postdocs, and early-career water researchers.

Mentorship plays a central role in Hannah’s life. As an undergraduate, she was placed in a program for students considered less likely to succeed. That experience, and the support it provided, helped define her approach to science and mentoring. “Everything I’ve accomplished is because mentors positively influenced the trajectory of my life, and I would love to provide that same support for others,” she says. “Mentoring students and seeing them advance on their own paths is one of my proudest achievements.”

In fall 2025, she will lead the mentorship program for the NAWI NextGen Leadership Committee. She is eager to involve mentees in the process and help early-career researchers connect and grow. As part of the program last year, Hannah advised Ph.D. students on maximizing productivity, finding early-career positions, and achieving a healthy work-life balance. As for the latter, she shares straightforward advice for Ph.D. students: “Take breaks, get outside, and stay proactive about communication with your mentor and collaborators.”

Outside the lab, Hannah enjoys walking around campus, spending time in nature, and playing with her cat, Friday. During the final year of her Ph.D., a visit to Climeworks’ direct air capture facility in Switzerland reminded her that the technologies she works on aren’t just theoretical—they are already being deployed. The site, one of the world’s first commercial-scale direct air capture plants, used modular units to extract carbon dioxide directly from the atmosphere for storage or reuse.

As she prepares to apply for faculty positions in chemical engineering, she stays focused on what initially drew her to science—curiosity and a desire to make a difference—along with what has sustained her commitment: mentoring the next generation of scientists and engineers.