Dialysis is traditionally employed in medicine to filter waste and excess fluid from the blood of patients with kidney failure. Blood is passed through a dialyzer, where it is cleansed before being returned to the body. Inspired by this medical technology, researchers have adapted the method to address industrial wastewater challenges.
"Dialysis was astonishingly effective in separating the salts from the organics in our trials," said Menachem Elimelech, a corresponding author of 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."
High-salinity organic wastewaters, common in industries such as petrochemicals, pharmaceuticals, and textiles, are notoriously difficult to treat. Current methods like biological treatment and advanced oxidation are often hampered by high salinity, while thermal methods are energy-intensive and prone to operational inefficiencies. Pressure-driven membrane processes frequently face membrane fouling, necessitating extensive wastewater dilution and complicating operations.
"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 of these pain points, reducing water consumption and operational overheads."
The research team conducted bench-scale dialysis experiments combined with detailed transport modeling to assess dialysis's effectiveness. Using commercial ultrafiltration membranes with varied molecular weight cutoffs, they investigated salt transport and organic rejection. A bilateral countercurrent flow setup enabled wastewater and freshwater streams to flow on opposite sides of the membrane without hydraulic pressure. Salts diffused into the dialysate, leaving the organics concentrated in the original solution.
The researchers measured performance by tracking salt and water fluxes, analyzing organic concentrations before and after dialysis, and evaluating membrane resistance to fouling during prolonged operation. Mathematical models were developed to further explore the mechanisms behind salt and water transport.
Results showed dialysis effectively separated salts from small, neutral organic molecules without requiring large amounts of fresh water. This diffusion-driven process enabled salts and organics to move across the membrane at different speeds, enhancing separation efficiency compared to ultrafiltration.
"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 notable advantage of dialysis is its resistance to fouling. Unlike pressure-driven systems, which often suffer from organic material buildup, dialysis avoids hydraulic pressure, resulting in lower energy use, reduced maintenance needs, 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 at Guangdong Tech's School of Ecology, Environment, and Resources. "This allows for a more stable and consistent performance over extended operating cycles."
While dialysis alone doesn't completely purify wastewater, it effectively reduces salinity, making advanced treatments like biological processes 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."
Research Report:Dialysis opens a new pathway for high-salinity organic wastewater treatment
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