Research Highlight

Inland brackish groundwater desalination has the potential to expand water supplies in water-scarce areas, but adoption is constrained by the high costs and environmental impacts of concentrate (brine) disposal. Brine valorization—selectively extracting marketable products from desalination brines—offers a pathway to offset disposal costs, reduce environmental impacts, and improve economic feasibility. The challenge is that market potential depends both on technical recoverability of constituents and the ability of local or regional markets to absorb them.

To combat this challenge, a team of NAWI researchers, led by Alison Fritz at the National Energy Technology Laboratory (NETL), along with Alexander Dudchenko (SLAC), Casey De Finnda (UC Davis), and Meagan Mauter (Stanford), focused on two objectives. First, to develop a geospatially resolved market assessment that identified existing and potential markets for bulk constituents by pairing brine composition and expected volumes with market data on building materials, fertilizer, road salts, and chemicals, including caustic soda and hydrochloric acid. Second, to conceptualize and develop process models for brackish groundwater treatment and valorization and perform an economic and life cycle assessment of the proposed treatment.

To achieve the first goal, the project team used the U.S. Geological Survey brackish water databases to quantify volume and composition of groundwater sources across the United States. By pairing this volume and composition data with regional market demand for building materials, fertilizers, road salts, and industrial chemicals, the team conducted mass balances to determine how much recovered material local markets could realistically absorb. Next, to model the performance and costs of these prospective systems, they used NAWI’s WaterTAP platform to construct a digital reference treatment train. They then built a superstructure optimization model capable of evaluating the costs of thousands of candidate process configurations for treatment and valorization.

The preliminary optimization results indicate that in most scenarios, byproduct valorization is not the economically optimal configuration. The costs of the extraction schemes can outweigh the low market value of the recovered commodities. However, for certain water chemistries it can be valuable. For example, in highly saline scenarios, generating sodium chloride for road salt and hydrochloric acid and sodium hydroxide yielded outcomes that reduced net water treatment costs. The project also learned through stakeholder engagement that adaptable technologies that allow valorization decisions to follow market trends can improve the economics in volatile product markets.

Read the project brief and check out the project poster to learn more. To learn more about WaterTAP, register for NAWI’s upcoming webinar.

Conventional scale mitigation methods—anti-scalant addition, ion-exchange resins, and solvent extraction—require significant chemical or thermal inputs, which complicate brine management. While electrodialysis (ED) can potentially separate mono- and divalent ions, current membranes lack the selectivity needed for effective scaling control.

This project, led by Jovan Kamcev at the University of Michigan with partners at Lawrence Berkeley National Laboratory and Veolia WTS, focuses on developing highly selective ion-exchange membranes to improve ED pretreatment for brackish water reverse osmosis (BWRO). The developed membranes could enable high-recovery BWRO processes that are chemical-free and energy-efficient, improving brackish water desalination sustainability and reducing concentrate management challenges.

These membranes were tested in bench-scale ED systems to determine their ability to reduce scaling potential in RO processes. Process modeling was employed to optimize operational parameters, including water recovery and energy consumption, for maximum efficiency.

Testing revealed that divalent-selective single-layer membranes achieved Ca²⁺/Na⁺ selectivity values of approximately 4 at low current densities, a performance level notably higher than that of commercial membranes. Monovalent-selective bilayer membranes exhibited extremely high Na⁺/Ca²⁺ selectivity across various brackish water chemistries; however, their ion transport fluxes were about an order of magnitude lower, reflecting the reduced limiting current density inherent to the design. Membranes featuring sulfonate and phosphate functional groups demonstrated the best Ca/Na separation factors under realistic brackish water compositions, indicating strong potential for practical scaling control.

Following bench-scale validation, the membranes will be scaled up for pilot plant demonstrations in collaboration with an industrial partner. A technoeconomic analysis will also be conducted to evaluate the commercial viability and overall feasibility of these pretreatment solutions.

The next phase will focus on conducting ED experiments using larger membrane stacks, with findings intended to calibrate the ED process model developed by WaterTAP. This progression marks a significant step toward bridging bench-scale insights with pilot-scale application readiness.

Access the project poster for more information.

Current reverse osmosis and nanofiltration membranes, which are often extremely delicate and thin, generally do not tolerate waters with suspended solids or high loadings of organics. Pretreatment is nearly always employed to reduce these contaminants which can foul or even abrade membranes. Current pretreatment approaches rely on decades-old technology, are expensive or chemically intensive, and can constitute a majority of the system footprint. They are also difficult to adapt for different treatment systems and typically struggle to entirely prevent fouling.

NAWI’s 5.22 project, “Printed Polyelectrolyte Complex (APEC) Membranes for Ultra-high Permeance Nanofiltration,” aims to create the first nanofiltration (NF) membranes for universal pretreatment. These NF membranes would streamline the pretreatment process to be more efficient across different types of treatment systems or water sources while simultaneously saving costs, energy, and treating more water with better output quality.

This project achieve this using a newly developed additive manufacturing process. This process, known as electrospray, which uses high voltage to induce fine, nano-scale sprays to deposit thin and defect-free layers of polymer electrolyte and produce multi-layered membranes with better control. This technique, called “electrospray additive manufacturing,” can form exceptionally thin (~10s of nanometers per layer or less) and defect-free films from any solution-processable polymer.

Electrospray is suited for forming amphiphilic polyelectrolyte complexes (APECs), which bring the positively and negatively charged polymers together to form a material that is both hydrophilic and hydrophobic. These specific properties of APECs create a stronger, adjustable material that better prevents fouling. By using numerous yet exceedingly thin bilayers, the goal of the research is to prevent membrane defects and make pretreatment more efficient, while creating NF membranes with the potential for 5-10 times higher permeance than commercial NF membranes made today.

Journal of Membrane Science | 3 July 2024

This study investigated the transport of water and 14 organic solvents across 16 dense polymer membranes with varying fractional free volumes. To read the academic journal article, visit this webpage.

Journal of Membrane Science | 1 July 2024

This study explores the role of the polysulfone (PSU) support membrane skin-layer and whole-body pore morphology on the physical-chemical properties and separation performance of hand-cast polyamide-PSU (PA-PSU) composite seawater reverse osmosis (SWRO) membranes. To read the academic journal article, visit this webpage.

ACS ES&T Engineering | 31 May 2024

This work focuses on real-time fault detection and showcases innovative methods for long-term monitoring of ultrafiltration membrane systems involving supervised and unsupervised machine learning. To read the academic journal article, visit this webpage.

Research supported by NAWI looks into the design of hybrid membrane systems using a forward osmosis- reverse osmosis (FO-RO) hybrid system. The study demonstrates how some membrane systems can exhibit self-regulating behavior due to a tendency for systems like these to move toward thermodynamic equilibrium. The researchers show how some membrane systems can leverage thermodynamics, rather than expensive control systems, to achieve steady state operation. Read the paper.

Research financed by NAWI uses an advancement of the refined e-NRTL model for the modeling of osmotic and activity coefficients associated with aqueous multi-electrolyte systems, with an emphasis on electrolyte systems relevant to concentrated brine solutions. The results are presented in a paper in the journal of Computer Aided Chemical Engineering. Read the paper.

In a paper published in the Journal of Resources, Conservation and Recycling, NAWI-supported researchers calculate the water reduction potential in United States manufacturing from commercially available water efficiency opportunities specific to the manufacturing sector. The research demonstrates that significant opportunities for water and energy use reductions at levelized costs at least one order of magnitude lower than alternative water supplies, with some being revenue-generating. Read the paper.

Research financed by NAWI used data from an engineering-scale ultrafiltration system treating reclaimed wastewater to assess the impact of backwashing on the filtration process. The results are presented in a paper titled ‘Analysis of backwash settings to maximize net water production in an engineering-scale ultrafiltration system for water reuse’ published in the Journal of Water Process Engineering. Read the paper.

NAWI-funded research compared the performance of antiscalants to an alternating, current-induced electromagnetic field (EMF) as an alternative pretreatment method to reverse osmosis. The research, published in the journal Water, demonstrated the synergistic effects of using an EMF in combination with antiscalants and could lead to lower pretreatment costs. Read the paper.

NAWI Research Director Meagan Mauter and her colleague authored an article for ACT ES&T Engineering that introduces the use of comparative infrared microscopy for directly measuring membrane thermal conductivity in highly porous membrane materials. Their measurements confirm that membrane morphology plays a significant role in effective membrane thermal conductivity and suggest that morphology can guide the selection of theoretical models for approximating membrane thermal conductivity when direct measurements are not possible. Read the paper.

After 2 years of postponed, canceled, or remote scientific interactions, the NAWI research community has been well represented at summer water research conferences. These conferences have been venues for sharing the results of NAWI’s early R&D accomplishments (roadmaps, baselines, WaterTAP, WaterDAMS, research outputs, etc.) and an opportunity to take stock of NAWI’s influence on the water desalination field more broadly. Below are several highlights from NAWI Research Consortium and Alliance members who attended the conferences and noted the degree to which NAWI’s research agenda has influenced the direction of water treatment across the broader research community.

NAMS 2022: Phoenix, AZ

Profs. Manish Kumar of UT Austin (a NAWI project performer and Beamline Characterization Advisory Council member) and Mary-Laura Lind of ASU hosted the North American Membrane Society annual meeting in Phoenix, AZ. A hybrid remote and in-person conference, this well attended set of workshops and conferences offered the first opportunity for the membrane community to come together after release of our roadmapping and baselining products. Manish mentioned that “NAWI roadmaps and NAWI supported research has shifted the conversation in the membrane community (as seen in NAMS meetings) and in the environmental engineering community more broadly towards electrification of water treatment and a focus on resource recovery in a significant way. Interest in oxyanion pollutant treatment has also grown as a result of NAWI activities as seen in presentations on these topics.”

AEESP 2022: Washington University in St. Louis

Prof. Dan Giammar of WUSTL (a NAWI Cartographer) was the co-chair of the AEESP conference held on the beautiful WUSTL campus. The agenda focused on convergence research, highlighting (among other topics) ways in which research, practice, and entrepreneurship were critical to addressing issues in water, climate, and sustainability. Dan noted that “a substantial number of the 320 abstracts submitted to the 2022 AEESP Research and Education Conference were focused on advanced water treatment processes. When our program committee had to determine an effective way for thematically grouping the presentations, the best framework that emerged was based on A-PRIME. Electrified treatment processes, modular membrane systems, and precision separations were all highlighted in the conference program.”

Other highlights included NAWI Next-Gen Katie Weitzel winning the best poster award at AEESP for her research on “Treatment and Reuse of Agricultural Drainage Water: Challenges and Opportunities” and Dr. Tim Bartholomew, Dr. Dan Gunter, Prof. Daniel Gingerich and myself hosting a pre-conference workshop with 90+ registrants on NAWI’s WaterTAP and WaterDAMS tools. (All materials are available here, for those of you unable to make the workshop, but are interested in learning more!) The highlight of the conference for me was seeing Amy Childress’ (a NAWI Cartographer) group at USC present on their cooling water treatment baseline analysis using NAWI’s WaterTAP tools.

GRC in Membranes: Materials and Processes

NAWI Deputy Topic Area Lead Jeff McCutcheon and several NAWI research consortium and Alliance members are attending the GRC in Membranes: Materials and Processes as you read this dispatch. Having seen a preview of the invited speakers, Jeff anticipates tremendous interest and lively discussion around Daniel Miller’s (LBNL) presentation of his NAWI-funded project on Computational and Experimental Test Beds for Prediction of RO Module Fouling. Jeff also noted that “NAWI has had a big impact on the membrane science community, particularly by highlighting the critical need for innovation in brine management as a key opportunity to lower the cost and energy use for desalination in the United States.”

Several other upcoming conferences will afford additional opportunities for NAWI to disseminate research results and share our collective vision for accessing non-traditional water at pipe parity through innovations in A-PRIME. We also look forward to hearing about innovations in the field, successes that change the R&D landscape in one or more A-PRIME areas, or new research directions that NAWI should consider allocating funding toward.

An article called Salt and Water Transport in Reverse Osmosis Membranes: Beyond the Solution-Diffusion Model was published in the December issue of Environmental Science and Technology (Environ. Sci. Technol. 2021, 55, 16665−16675). The publication is authored by researchers at Yale University in the U.S. and Wageningen University and WETSUS in the Netherlands, including Li Wang, Tianchi Cao, Jouke E. Dykstra, Slawomir Porada, P. M. Biesheuvel, and Menachem Elimelech.

This article, along with a companion publication in the Journal of Membrane Science by the same three institutions, describes an important breakthrough in how to more accurately model water and salt transport in thin film composite membranes. The Water Desalination Report, the leading industry trade communication on desalination, devoted an entire page to summarizing the findings outlined in the article.

We spoke with Professor Menachem Elimelech, Sterling Professor of Chemical and Environmental Engineering at Yale University, about the research. “Basically, I had been irritated for a long time,” he explains. “The solution-diffusion model treats membranes as a black box…dissolving and diffusing without considering the unique chemistry and pathways [for transport through real membranes]. What bothered me even more: it hinders development of water and solute transport improvements. For example, why do some membranes reject boron well and not others?”

To address the limitations of the long-standing solution-diffusion model, Elimelech and his collaborators formulated a new “solution-friction” model in which “ion transport through the membrane is described by the extended Nernst−Planck equation, with the consideration of friction between the species (i.e., ion, water, and membrane matrix). Water flow through the membrane is governed by the hydraulic pressure gradient and the friction between the water and membrane matrix as well as the friction between water and ions.” The model does an excellent job of matching experimental results using only 2 fitting parameters. Read the journal article Salt and Water Transport in Reverse Osmosis Membranes: Beyond the Solution-Diffusion Model.

This publication covers topics such as:

Open-access database of reverse osmosis membrane performance and characterization data.
User-sourcing for transparent sharing of experimental results.
Dynamic environment for membrane comparisons and analyses under uniform reporting conditions.
Optimal platform for developing databases for other commonly used membrane separation technologies.

Read the full publication.

Published in PNAS, September 14, 2021. Access the publication.

Researchers lack the tools for quantitatively evaluating the impact of their research on technology costs, especially when those technologies comprise multiple components or when the component costs are highly uncertain. We propose a suite of tools to aid in evaluating technology platforms, setting system- and component-level research targets and identifying high-impact innovation trajectories. These tools are applicable to any technology composed of multiple components whose performance or cost will benefit from innovation, but they are especially valuable for membrane systems in which the high interdependence in components amplifies or dampens the effects of innovation in nonintuitive ways.

Lead author Jason Yang from NAWI Consortium Member Yale University discusses the results of molecular dynamics simulations examining the removal of small organic contaminants in water with nanoporous graphene membranes. Read about this research.