In a recent study published in Nature Water, researchers from Rice University and the Guangdong University of Technology have discovered a novel method for treating high-salinity organic waste waters, or streams with high salt and organic material levels, using dialysis, a technique borrowed from the medical industry.
Menachem Elimelech and Yuanmiaoliang “Selina” Chen. Image Credit: Gustavo Raskosky/Rice University
Dialysis for patients with kidney failure involves drawing blood from the patient, cleaning it in a device called a dialyzer, and then returning it through a different needle or tube.
The team discovered that by simulating this process, salts and organic materials can be separated from wastewater with little dilution while addressing important drawbacks of traditional techniques. Across a variety of industrial sectors, this innovative pathway could enable the recovery of valuable resources, lower costs, and lessen environmental impacts.
Dialysis was astonishingly effective in separating the salts from the organics in our trials. It’s an exciting discovery with the potential to redefine how we handle some of our most intractable wastewater challenges.
Menachem Elimelech, Study Corresponding Author, Rice University
Menachem Elimelech is the Nancy and Clint Carlson Professor of Civil and Environmental Engineering and Chemical and Biomolecular Engineering.
Various industries produce high-salinity organic wastewater, such as textile, pharmaceutical, and petrochemical production. Due to their high organic content and combined high salt content, these wastewaters present significant difficulties for current treatment procedures. High salinity levels frequently jeopardize biological treatment and sophisticated oxidation techniques, decreasing efficacy.
Although technically possible, thermal methods are energy-intensive and prone to clogging, corrosion, and operational inefficiencies, increasing expenses and making maintenance more difficult. In the meantime, severe membrane fouling is common in pressure-driven membrane processes like ultrafiltration, necessitating several wastewater dilution steps that raise operational complexity and water consumption.
Traditional methods often demand a lot of energy and require repeated dilutions. Dialysis eliminates many of these pain points, reducing water consumption and operational overheads.
Yuanmiaoliang “Selina” Chen, Study Co-First Author and Postdoctoral Associate, Rice University
The research team used both extensive transport modeling and bench-scale dialysis experiments to assess the effectiveness of dialysis in removing salts and organic compounds. The researchers first chose commercial ultrafiltration membranes with various molecular weight cutoffs to investigate salt transport and organic rejection.
The scientists subsequently created a bilateral countercurrent flow mode in the dialysis setup. This involved a freshwater stream flowing on one side of the membrane without any hydraulic pressure applied, and a feed stream comprising high-salinity organic wastewater passing on the other.
The researchers monitored the salt and water fluxes over time to show that salts diffused across the membrane into the dialysate while water flux remained insignificant. By comparing the levels of organic matter in the feed before and after dialysis, the scientists could quantify the amount of organic removal.
During long run times, they monitored any changes in membrane performance to gauge fouling resistance. The researchers expanded their knowledge of the mechanisms underlying salt and water transport by creating mathematical models.
The scientists discovered that dialysis successfully eliminated salt from water without using a lot of fresh water. Most organic compounds remained in the original solution, but salts could enter the dialysate stream.
Dialysis outperformed ultrafiltration in separating salts from small, neutral organic molecules using the same membrane. As dialysis relies on diffusion rather than pressure, salts and organics traversed the membrane at varying speeds, enhancing separation efficiency.
“We found that one of the biggest advantages of dialysis for wastewater treatment is the potential for resource recovery. Beyond simply treating the wastewater, we can also recover valuable salts or chemicals, contributing to a more circular economy,” said Menachem Elimelech.
Another key advantage of dialysis is its high resistance to fouling. Since dialysis does not rely on hydraulic pressure, it saw less organic material accumulation on the membrane than pressure-driven systems. This may result in less maintenance, less energy consumption, 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. This allows for a more stable and consistent performance over extended operating cycles.
Zhangxin Wang, Study Co-Corresponding Author and Professor, School of Ecology, Environment and Resources, Guangdong University of Technology
Furthermore, dialysis efficiently lowers salinity, which increases the effectiveness of other treatments like biological processes, advanced oxidation, or zero-liquid discharge systems, even though it cannot completely purify wastewater on its own.
“Dialysis offers a sustainable solution for treating complex, high-salinity waste streams by conserving freshwater, reducing energy costs, and minimizing fouling. Its diffusion-driven approach could revolutionize the treatment of some of the most challenging industrial wastewaters,” said Elimelech.
Journal Reference:
Chen, Y., et al. (2024) Dialysis opens a new pathway for high-salinity organic wastewater treatment. Nature Water. doi.org/10.1038/s44221-024-00368-6