At the Elimelech group, we are leading advancements in membrane-based technologies to address the critical challenges of sustainable desalination and wastewater management. As global water scarcity intensifies, reverse osmosis (RO) has become the dominant desalination method due to its energy efficiency and cost advantages over thermal alternatives. However, the process generates highly concentrated brine, which poses significant environmental, operational, and economic challenges. Brine management becomes increasingly complex as total dissolved solids (TDS) in the feedwater rise, causing a non-linear increase in osmotic pressure, as shown in Figure 1.

High osmotic pressure directly influences energy demands, with a minimum specific energy consumption (SEC) of 2.22 kWh/m³ required to achieve 80 bars, a common operating pressure in seawater desalination. This increases to 3.33 kWh/m³ at 120 bars, the limit for current high-pressure reverse osmosis membranes. Real-world inefficiencies, including irreversible losses from pressure and mass transfer, further exacerbate energy consumption and restrict the maximum achievable brine concentration, underscoring the need for innovative solutions.

Our research addresses these challenges through membrane brine concentration (MBC) approach.These technologies aim to reduce energy consumption, achieve minimal and zero liquid discharge (M/ZLD), and enable resource recovery, transforming brine from a waste product into a valuable resource. By optimizing membrane materials and system designs, we seek to enhance water recovery, lower environmental impacts, and improve cost efficiency. Furthermore, we explore the scalability of these solutions to meet the growing global demand for sustainable water treatment. Through rigorous scientific investigation and practical application, our work bridges the gap between innovation and real-world implementation, advancing the field toward a more resource-efficient and sustainable future.

Low-Salt-Rejection Reverse Osmosis (LSRRO)

Our lab is at the forefront of exploring low-salt-rejection reverse osmosis (LSRRO), a promising technology for high-efficiency brine concentration. LSRRO can concentrate brines up to 250 g/L with significantly lower hydraulic pressures than high-pressure reverse osmosis (HPRO) or ultra-high-pressure reverse osmosis (UHPRO). The process begins with a high-rejection RO stage to produce fresh water, followed by subsequent LSRRO stages using membranes with declining partial salt rejection. Permeate from these stages is recycled into preceding stages to reduce feed salinity. This multi-stage process is supported by energy recovery devices (ERDs) that recover residual pressure from brine streams, further reducing energy demands.

While LSRRO’s complex design results in higher capital costs and larger system footprints, it benefits from leveraging established nanofiltration (NF) manufacturing technologies, reducing the barriers to commercial adoption. Our research focuses on optimizing LSRRO systems and exploring their hybridization with HPRO and UHPRO to simplify designs and improve efficiency. This hybridization could significantly reduce the number of required stages, making the technology more cost-effective and scalable. By advancing LSRRO, we aim to unlock its full potential as a commercially viable solution for sustainable brine management.

High Pressure Reverse Osmosis (HPRO)

Conventional seawater RO, operating under 80 bar, is limited to concentrating brines with total dissolved solids (TDS) below 95 g/L due to osmotic pressure constraints. To overcome this, the introduction of high-pressure reverse osmosis (HPRO) membranes capable of withstanding pressures up to 120 bar has marked a significant breakthrough. These membranes can concentrate brines up to 135 g/L TDS, but their performance is hindered by physical compaction, which reduces water permeability, and by potential damage from membrane embossing at high pressures.

Our ongoing research focuses on developing ultra-high-pressure reverse osmosis (UHPRO) membranes that are resistant to compaction and capable of operating at pressures up to 200 bar. This includes advancements in membrane materials and module designs to enhance durability and scalability. By addressing these challenges, HPRO and UHPRO technologies could revolutionize brine concentration processes, making them more efficient and cost-effective for large-scale desalination and brine management applications.

Dialysis

Inspired by medical dialysis, which removes metabolic waste (e.g., urea) while preserving essential blood components (e.g., red blood cells), we have proposed the innovative application of dialysis for the selective fractionation of salts and organic matter in wastewater. This approach addresses the limitations of conventional treatment technologies in managing high-salinity organic wastewaters, offering a sustainable and efficient alternative.

In dialysis, wastewater is brought into contact with a dialysate solution across a semi-permeable membrane that selectively permits the transport of salts while rejecting organic substances. The lower salinity of the dialysate creates a concentration gradient, driving the diffusion of salts from the wastewater to the dialysate, facilitating the effective separation of salts from organic compounds. Our previous work has demonstrated that, by eliminating hydraulic pressure and transmembrane water permeation, dialysis prevents wastewater dilution, enhances salt/organic selectivity, and minimizes fouling risks. This novel approach offers significant potential to reduce environmental impact, lower operational costs, and enable resource recovery across various industrial sectors, providing clear advantages over conventional membrane processes. Our ongoing research focuses on optimizing dialysis for improved salt/organic selectivity and developing guidelines for membrane selection tailored to wastewaters from different industries, further advancing its application in the sustainable treatment of challenging wastewaters.

Representative Publications

Chen, Y., Wang, L., del Cerro, M., Wang, L., Zhang, X., Elimelech, M & Wang, Z., “Dialysis opens a new pathway for high-salinity organic wastewater treatment.” Nature Water, 3, 49-58 (2025). https://doi.org/10.1038/s44221-024-00368-6

Wu, J., Elimelech, M., et al. “Polyamide reverse osmosis membrane compaction and relaxation: Mechanisms and implications for desalination performance.” Journal of Membrane Science, 706, 122893 (2024). https://doi.org/10.1016/j.memsci.2024.122893

Du, Y., Wang, Z., Cooper, N. J., Gilron, J., & Elimelech, M., “Module-scale analysis of low-salt-rejection reverse osmosis: Design guidelines and system performance.” Water research, 209, 117936 (2022). https://doi.org/10.1016/j.watres.2021.117936

Wang, Z., Deshmukh, A., Du, Y., & Elimelech, M., “Minimal and zero liquid discharge with reverse osmosis using low-salt-rejection membranes.” Water research, 170, 115317, (2020). https://doi.org/10.1016/j.watres.2019.115317

Davenport, D.M., Deshmukh, A., Werber, J. R., & Elimelech, M., “High-pressure reverse osmosis for energy-efficient hypersaline brine desalination: current status, design considerations, and research needs.” Environmental Science & Technology Letters, 5, 467-475 (2018). https://doi.org/10.1021/acs.estlett.8b00274