Borrowing from the medical field, dialysis can separate substances while achieving minimal dilution, generating a unique pathway for wastewater treatment.
In collaboration with the Guangdong University of Technology, Rice University researchers have uncovered an innovative approach to treating high-salinity organic wastewater streams containing elevated salt and organic concentrations. The approach employs dialysis, a technology borrowed from the medical field.
Dialysis uses a machine called a dialyzer to filter waste and excess fluid from the blood of patients with kidney failure. Blood is drawn from the body, cleansed in the dialyzer, and returned through a separate needle or tube.
In a new study published in Nature Water, the team found that mimicking this same method can separate salts from organic substances with minimal dilution of the wastewater, simultaneously addressing key limitations of conventional methods. This novel pathway can potentially reduce environmental impacts, lower costs, and enable the recovery of valuable resources across various industrial sectors.
“Dialysis was astonishingly effective in separating the salts from the organics in our trials,” said Menachem Elimelech, a corresponding author on the study and the Nancy and Clint Carlson Professor of Civil and Environmental Engineering and Chemical and Biomolecular Engineering. “It’s an exciting discovery with the potential to redefine how we handle some of our most intractable wastewater challenges.”
Numerous industries generate high-salinity organic wastewater, including petrochemical, pharmaceutical and textile manufacturing. These wastewaters pose serious challenges for existing treatment processes because of the combined high salt and high organic content. Elevated salinity levels often compromise biological treatment and advanced oxidation methods, reducing their overall effectiveness.
Although technically feasible, thermal methods are energy-intensive and susceptible to corrosion, clogging, and operational inefficiencies that can escalate costs and complicate maintenance. Meanwhile, pressure-driven membrane processes such as ultrafiltration frequently encounter severe membrane fouling, leading to the need for multiple wastewater dilution steps, which increases water usage and operational complexity.
“Traditional methods often demand a lot of energy and require repeated dilutions,” said Yuanmiaoliang “Selina” Chen, a co-first author and postdoctoral student in Elimelech’s lab at Rice. “Dialysis eliminates many pain points, reducing water consumption and operational overheads.”
The research team used bench-scale dialysis experiments and comprehensive transport modelling to evaluate dialysis performance in separating salts and organic compounds. First, they selected commercial ultrafiltration membranes with different molecular weight cutoffs to study salt transport and organic rejection. They then established a bilateral countercurrent flow mode in the dialysis setup, including a feed stream containing high-salinity organic wastewater on one side of the membrane. In contrast, a freshwater stream flowed on the other side without any applied hydraulic pressure.
The researchers tracked salt and water fluxes over time to demonstrate that salts diffused across the membrane into the dialysate while water flux remained negligible. They measured organic removal by comparing organic concentrations in the feed before and after dialysis. To assess fouling resistance, they monitored changes in membrane performance, if any, during extended run times. The researchers further developed mathematical models to deepen their understanding of salt and water transport mechanisms.
They found that dialysis effectively removed salt from water without requiring large amounts of fresh water. The process allowed salts to move into the dialysate stream while keeping most organic compounds in the original solution. Compared to ultrafiltration with the same membrane, dialysis better-separated salts from small, neutral organic molecules. Since dialysis relies on diffusion instead of pressure, salts and organics cross the membrane at different speeds, making the separation more efficient.
“We found that one of the biggest advantages of dialysis for wastewater treatment is the potential for resource recovery,” Elimelech said. “Beyond simply treating the wastewater, we can also recover valuable salts or chemicals, contributing to a more circular economy.”
Another significant advantage of dialysis is its resistance to fouling. Unlike pressure-driven systems, dialysis experienced notably less buildup of organic materials on the membrane because it doesn’t rely on hydraulic pressure. This could translate to lower energy use, less maintenance and fewer membrane replacements.
“By forgoing hydraulic pressure altogether, we minimized the risk of fouling, which is one of the biggest hurdles in membrane-based treatment,” said Zhangxin Wang, a co-corresponding author and professor in the School of Ecology, Environment and Resources at Guangdong Tech. “This allows for a more stable and consistent performance over extended operating cycles.”
Moreover, while dialysis alone doesn’t fully purify wastewater, it effectively reduces salinity, making other treatments—such as biological processes, advanced oxidation, or zero-liquid discharge systems—more efficient.
“Dialysis offers a sustainable solution for treating complex, high-salinity waste streams by conserving freshwater, reducing energy costs and minimizing fouling,” Elimelech said. “Its diffusion-driven approach could revolutionize the treatment of some of the most challenging industrial wastewaters.”
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