Combined Electrodialysis and Pressure Membrane Processes for Removal of Natural Organic Matter in Drinking Water Sources
Physical Sciences : Materials and Compounds
Available for licensing
- Lynn Katz, Ph.D. , Civil, Architectural and Environmental Engineering
- Desmond Lawler, Ph.D. , Civil, Architectural and Environmental Engineering,
- Soyoon Kum, M.S. , Civil, Architectural and Environmental Eng
Natural organic matter (NOM) is ubiquitous in surface waters (lakes, rivers) and can also occur in groundwaterl. NOM is problematic in water treatment because it reacts with chemicals added as disinfectants to form disinfection by-products (DBPs), many of which are known or suspected carcinogens. NOM removal is dictated by USEPA regulations in the "Disinfection/Disinfection By-Product (D/DBP) Rule."
Current approaches to dealing with DBPs involve removing DBPs after they are formed, using alternative disinfectants to reduce DBP formation, and/or removing the NOM from the water before or simultaneously with disinfection. For some utilities, none of these approaches is entirely satisfactory, and the problem of balancing disinfection needs of drinking water and DBP production has been the central problem facing water utilities for more than three decades.
Researchers at The University of Texas at Austin have developed a novel system designed to effectively treat waste water that is high in natural organic matter. The invention is a unique combination of existing water treatment technologies and is designed to remove NOM from water sources, primarily surface water sources, of drinking water. The process is to be used prior to chlorination. It makes use of the principles of membrane processes (e.g., electrodialysis, reverse osmosis, nanofiltration) and an understanding of water chemistry to isolate NOM from water while maintaining an ion content appropriate for drinking water.
- Other processes designed for removal of NOM, such as enhanced coagulation or activated carbon adsorption are either less effective, operationally challenging and/or potentially more expensive. For example, it is rare for enhanced coagulation to achieve more than 40% removal of DOC, and for many waters, removing even 15% of the DOC by this technique is difficult or impossible.
- The invention described here will be capable of achieving far higher DOC removals and the removal efficiency will be far less dependent on the source water characteristics.
- This invention uses electrodialysis (ED) in tandem with either nanofiltration (NF) or reverse osmosis (RO). ED separates the influent water into a "concentrate" stream which contains a high fraction of ions present in the original water and a "diluate" stream, which contains a much lower concentration of the original ions. It is very efficient in transporting inorganic ions into these two streams, but NOM, although it is generally negatively charged in drinking water sources, is not removed well.
- In our unique configuration and operation, the diluate from the ED is fed to either a nanofiltration (NF) membrane or a reverse osmosis (RO) membrane. These processes also separate the water into concentrate and diluate streams. In this case, the NOM will largely be prevented from passing through the membrane and virtually all will be in the concentrate stream.
- Finally, the concentrate stream from the ED system(s) and the diluate stream from the RO/NF process will be combined; this water should have a high fraction of the original volume of water, a similar high fraction of the original inorganic ions and salts, but a greatly reduced mass (or concentration) of the original NOM.
This technology would be immediately useful to drinking water utilities that have a surface water source or a groundwater source that contains natural organic matter.
Proof of concept
- 1 U.S. patent application filed