Lauren Nicole Core

Republished with permission from the University of Illinois Urbana Champaign.

The nitrate runoff problem, a source of carcinogens and a cause of suffocating algal blooms in U.S. waterways, may not be all gloom and doom. A new study led by the University of Illinois Urbana-Champaign demonstrates an approach for the integrated capture and conversion of nitrate-contaminated waters into valuable ammonia within a single electrochemical cell.

The study, directed by chemical and biomolecular engineering professor Xiao Su, demonstrates a device capable of an eightfold concentration of nitrate, a 24-times enhancement of ammonium production rate and a greater than tenfold enhancement in energy efficiency compared with previous nitrate-to-ammonia electrocatalysis methods.

“By combining separation with reaction, we overcame previously existing limitations of producing ammonia directly from groundwater, where the concentrations of nitrate are very low, and thus make the conversion step inefficient,” Su said.

The findings are published in the journal Nature Communications.

“The goal of this study was to use as little energy as possible to remove nitrate from agricultural runoff before it hits our waterways, and transform it back to a fertilizer or sell it as a chemical feedstock,” Su said. “Our technology can thus have an impact on waste treatment, sustainable chemical production and advance decarbonization. We are hoping to bring greater circularity into the nitrogen cycle.”

The team developed a unique, bifunctional electrode that can separate and up-concentrate nitrate from a water stream, while converting to ammonia in a single unit using purely electrochemical control. “The bifunctional electrode combines a redox-polymer adsorbent, which captures the nitrate, with cobalt-based catalysts that drive the electrocatalytic conversion to ammonium,” Su said.

The system was tested in the lab using agricultural runoff collected from drain tiles around the U. of I. research farmlands to evaluate the potential of the technology for real-world conditions, the researchers said.

“This is a very efficient capture and conversion platform with a low footprint,” Su said. “We don’t need separate electrochemical cells for the water treatment and ammonium production or adding extra chemicals or solvents. Instead, we envision a module installed directly onto farmland and run using the power generated from the electrocatalytic process and a small solar panel.”

The team said its next goal is to develop even more selective materials used in the device to achieve higher nitrate removal and accelerate the conversion to ammonia – while engineering larger scale systems for practical deployment in the field.

Kwiyong Kim is the first author of the study, with contributions from Jaeyoung Hong and Jing Lian Ng, from the Su group. The work was carried out in collaboration with Tuan Anh Pham, from the Lawrence Livermore National Laboratory, and Alexandra Zagalskaya and Vitaly Alexandrov, from the University of Nebraska.

Su also is affiliated with the Beckman Institute for Advanced Science and Technology and also is a professor of civil and environmental engineering at Illinois.

The National Alliance for Water Innovation, funded by the U.S. Department of Energy and the Institute for Sustainability, Energy, and Environment at Illinois supported this study.

Editor’s notes:

To reach Xiao Su, call 217-300-0134; email .

The paper “Coupling nitrate capture with ammonia production through bifunctional redox-electrodes” is available online.

DOI: 10.1038/s41467-023-36318-1

In April 2022, a team of engineers hiked into California’s Sierra Nevada mountains to hunt for snow. Instead, they found mostly bare, dry dirt and only a few of the snow patches that provide one-third of California’s water supply.

In the coming decades, water scarcity and insecurity are likely to intensify across much of the United States. In California, the Sierra Nevadas are expected to lose a staggering 65% of their snowpack over the next century, said Hariswaran (Hari) Sitaraman, a researcher at the National Renewable Energy Laboratory. That loss, plus political, economic, and other challenges, is making it essential for drought-prone states, like California, to tap alternative water sources such as brackish (or salty) waters and agricultural runoff.

And yet, the most common way to treat and reuse nontraditional water supplies is through a process called reverse osmosis, which can be both expensive and energy intensive.

Now, Sitaraman and Ilenia Battiato, two members of the National Alliance for Water Innovation (NAWI) research consortium, have used supercomputers to study reverse osmosis systems as a whole—a first for both the type and scale of reverse osmosis research. With their new technique, the duo also discovered a new system design that could make these technologies about 40% more energy efficient—and therefore more cost-effective—while producing the same amount and quality of clean drinking water.

“Until now, people have been looking at a tiny piece of the entire reverse osmosis module and drawing conclusions from that,” Sitaraman said. “But we looked at the entire thing.”

The results are published in a new paper in Separation and Purification Technology.

Along with Battiato, an assistant professor of energy science and engineering at Stanford University, Sitaraman created a fluid dynamics solver—a numerical tool that can analyze how fluids, like salty water, flow into a reverse osmosis system, pass through several membrane filters, and come out clean on the other side.

With their solver, Sitaraman and Battiato studied reverse osmosis systems with high precision, enabling them to uncover any snags or inefficiencies. For example, to filter brackish waters, reverse osmosis systems use high pressure to push the water through several membranes, which, like sophisticated coffee filters, block salts and other minerals from passing through. That process cleans the water, but it also creates thin layers of salty buildup on the membranes. And that buildup can affect how well the water flows, potentially reducing the system’s efficiency.

“That thin layer needs to be measured correctly to understand how much pure water you get out of salt water,” Sitaraman said. “If you don’t capture that right, you cannot understand how much it costs to run a reverse osmosis plant.”

A more efficient reverse osmosis system is more cost-effective, too.

Yet, most reverse osmosis plant owners do not have a high-performance computer to replicate Sitaraman and Battiato’s high-fidelity simulations—which so accurately mimic real-life reverse osmosis technologies—to uncover snags in their own systems. So, Sitaraman performed the complex work of creating a simpler model equation that can predict a system’s mass transfer, estimating how much pure water can be filtered out of brackish water. With his model, engineers can now discover how to improve the efficiency (and cost) of their own systems.

“If the economics improve,” Sitaraman said, “then of course reverse osmosis systems will be more widely used. And if they’re more energy efficient, they will contribute less to greenhouse gas emissions and climate change.”

That is a huge win, but Sitaraman and Battiato’s tools can benefit far more than reverse osmosis plant owners. Other researchers can build on their work to study the efficiency and cost of all kinds of reverse osmosis filtration technologies beyond those used to treat unconventional water sources. The food industry uses these filters to create highly concentrated fruit juices, more flavorful cheeses, and much more. Aquariums need them to remove harmful chemicals from their waters. And reverse osmosis systems can even extract valuable minerals and other substances that could be used to make cheap fertilizer or fuel.

One huge advantage of high-fidelity simulations, Battiato said, is the ability to study a vast range of reverse osmosis system configurations without investing the time and money required to build and experiment with real-life systems.

“We want the system to correctly capture the physics,” Battiato said, “but we are theoretically not constrained by manufacturing.”

With simulations, the team can quickly explore far more potential designs and home in on the best. That is how Battiato and Sitaraman identified their potentially more effective arrangement of spacers (which are bits within the reverse osmosis system that create turbulence and keep channels open to help water flow through). Their new spacer arrangement not only improves the system’s energy efficiency by 40%, but it also produces the same amount of equally pure water.

Although the duo’s simulations accurately replicate real-life systems, they are still theoretical. Sitaraman hopes another research team will build their design and evaluate how closely the real system matches their models. In the meantime, their higher-resolution (or more precise and comprehensive) simulations could help researchers avoid making inaccurate assumptions about how reverse osmosis systems work and, in so doing, learn how to improve the technologies.

Today, most engineers use trial and error to discover how to improve their reverse osmosis systems. But that process is slow, and water shortages are coming fast. With Battiato and Sitaraman’s simulations, engineers could speed up the development of more efficient and cost-effective technologies, so the country can access unconventional water sources when communities—like drought-stricken western towns—desperately need them.

“Water is a scarce resource,” Battiato said. “I don’t think we can afford to do coarse optimization anymore. We need to save every drop of water that we can.”

Learn more about the National Alliance of Water Innovation and their efforts to secure an affordable, energy-efficient, and resilient water supply for the United States.

The National Alliance of Water Innovation is a public–private partnership that brings together a world-class team of industry and academic partners to examine the critical technical barriers and research needed to radically lower the cost and energy of desalination. The alliance is led by the U.S. Department of Energy’s Lawrence Berkeley National Laboratory in collaboration with the National Energy Technology Laboratory, the National Renewable Energy Laboratory, and Oak Ridge National Laboratory and is funded by the U.S. Department of Energy’s Industrial Efficiency and Decarbonization Office.

After a summer of COVID restrictions, travel and (hopefully) a bit of vacation, many of us are heading back into the office or classroom.  While we might not spend a great deal of time thinking about the implications for our water use at work, NAWI friends at Phoenix Process Equipment Co. and Aquacell Water Recycling Ltd. certainly do.  Over the past month, they have graciously hosted NAWI members on tours of the Salesforce Tower in San Francisco and Meta corporate campus in Menlo Park, CA (yes, that Meta) where they designed and installed onsite “blackwater” reuse facilities. They shared some important lessons in operating small-scale water treatment systems.

First the stats.  Both facilities were designed to accommodate large office populations and treat between 40 to 90 thousand gallons per day of rainwater, toilet, and sink wastewater to a quality safe for additional toilet flushing and/or irrigation (of salinity sensitive redwoods!). Both facilities used roughly the same process train consisting of belt filter (with solids discharged to sewer), aerobic membrane bioreactor system (MBR), RO, ultraviolet (UV), and remineralization. While the Salesforce system was idle at the time of our visit, Meta’s system was just getting restarted after a long COVID hiatus, and will be resuming water delivery in the coming weeks. 

Next the insights:  

1. COVID threw onsite systems a major curveball. Meta’s campus was fully populated before the 2.5 year-long COVID shutdown; the new “normal” office population (about one-third of pre-pandemic numbers) is sufficient to sustain the MBR, but is far below the original design capacity. We had some great discussions about resilient designs, including what it would take for systems to operate at a mere 10% of their design capacity for an extended period of time.  
2. Tanks, tanks, tanks! Water treatment and reuse systems require a LOT of water storage. This is often overlooked in academic studies. Not only are tanks expensive ($2-$10 per stored gallon) but they also have a significant footprint — not cheap when it means displacing coveted parking spots and valuable Silicon Valley real estate. Ideally, below-grade storage tanks are integrated into the original building design. Researchers probably need to do a better job of factoring storage into the total cost projections for on-site systems. 
3. Insensitivity (indifference?) to electricity consumption. During both of our tours, we had a hard time even finding the electrical meter and system designers often have no information about the actual system energy use once its installed and operating.
4. Odor and color control is essential. Office building tenants do NOT want to smell even a whiff of typical wastewater treatment plant “fragrance”, and tenants don’t want to flush their toilets with yellow water. A lot of our process designs for onsite blackwater reuse are dictated by odor and color rather than by safety concerns. We wondered aloud where NAWI technologies could make an impact in these two important aesthetic areas. 
5. Permitting blackwater recycling systems remains a regulatory challenge. While greywater recycling has become significantly easier to permit over the past decade, blackwater systems are really first-of-a-kind demonstration sites in most regions. They are often held to the same standards for daily monitoring, sample collection, and thus demand frequent sensor monitoring and calibration. Technology and regulations are going to have to evolve together for building-scale reuse to really take hold.
6. These systems are far too complex to be managed by a typical property manager or site engineer. Both sites we visited had real-time remote monitoring. The (operational) Meta facility had a dedicated Level 2 operator onsite, as well as a contract with a local laboratory for daily sampling collection/analysis. Additional facilities operation support and maintenance was a phone call away. 

Katie Weitzel and her team were awarded for their research poster titled Treatment and Reuse of Agricultural Drainage Water: Challenges and Opportunities. Weitzel, a Ph.D. student at the University of Cincinnati, attended the 2022 Association of Environmental Engineering and Science Professors (AEESP) Research and Education Conference to represent her work. 

“There were a lot of people interested in this work and I had a lot of interaction with people during the poster session,” said Weitzel. “It was nice to see so many people interested in this and starting discussions about treatment of non-traditional water sources.”

Weitzel and her team’s research focuses on water innovation surrounding agricultural drainage, and their poster presented information from the agricultural baseline work they’ve been investigating as part of the NAWI research consortium. The poster content complemented the conference theme, “Environmental Engineering at the Confluence,” which covered the full breadth of environmental engineering. The conference explored emerging developments in the field and focused four areas of convergence: convergence of education and research, convergence of research in air, water, and soil, convergence of research and action, and convergence of research, practice, and entrepreneurship.

 I was recently introduced to Prof. R. S. Silver’s 1979 history of desalination, slyly titled For want of a nail (Desalination Volume 31, Issues 1–3, October 1979, Pages 39-44). Silver summarizes his career in desalination research, noting that it is often the small things in desalination that end up mattering the most. 

This cautionary tale weighed on my mind when I recently toured the Advanced Water Treatment Plant (AWTP) located in Cambria, California. Prior to the development of the plant, Cambria had relied on groundwater from a nearby creek. The Central Californian local community knew it was time for a water-supply related change after years of low rainfall and over-reliance on a single water supply.  

Cambria’s AWTP⁠—a secondary water supply based on reuse of treated wastewater⁠—was thus built in 2015 during the height of California’s most recent multi-year drought. 

The picturesque town’s treated wastewater is first diverted to a percolation basin where it seeps into the subsurface. It then interacts with freshwater percolating from the mountains to the East and seawater seeping inland from the West. The mixed groundwater is then pumped out of the basin, filtered, and desalinated with a 2-stage Reverse Osmosis (RO) system. This RO system recovers 92% of the fresh water, which is then reintroduced into the town’s groundwater well-field further upslope. The MF-RO-UV-H2O2 unit processes of the packaged desalination facility are elegantly housed in a set of cargo containers, cleverly laid out so that the entire system resembles a set of large tan Legos.

Unfortunately, R. S. Silver’s admonition became particularly apparent once the system was up and running. The small amount of brine generated from the facility was disposed of by pumping it into an evaporation basin nearby. The evaporation basin itself was rigorously engineered to prevent leaks but… the cool foggy weather common for the central coast resulted in very low evaporation rates. And, when a winter storm caused runoff to overtop the basin, the entire water project was put on indefinite hold.

The entire “kingdom” of brackish desalination has been waiting for a brine disposal nail.

On a related note, NAWI has begun to review Concept Papers submitted in response to our recent call for proposals for piloting novel small-scale desalination systems (read the Pilot Program FAQ for more information). I am very hopeful that the desalination community will come forward with breakthrough approaches to further treating and reducing (or even eliminating?) the liquid brine waste stream that has bedeviled brackish desalination for so long.