EDR - Electro Dialysis Reversal
For low energy desalination (total TDS reduction) and process concentration
Membranes: standard grade homogeneous anion and cation exchange membranes
How does it work?
Electrodialysis (ED) is a DC voltage-driven membrane process. An electrical potential is used to move salts through a membrane, leaving fresh water behind as product water.
ED depends on the following general principles:
Most salts dissolved in water are ions, either positively charged (cations), or negatively charged (anions). Since two identical charged poles repel each other and two opposite poles attract, the ions migrate toward the electrodes with an opposite electric charge.
Suitable membranes can be constructed to permit selective passage of either anions or cations. In a saline solution, dissolved ions such as sodium (+) and chloride (-) migrate to the opposite electrodes passing through selected membranes that either allow cations or anions to pass through (not both).
Membranes are usually arranged in an alternating pattern, with anion-selective membrane followed by a cation-selective membrane. During this process, the salt content of the water channel is diluted, while concentrated solutions are formed at the electrodes. Concentrated and diluted solutions are created in the spaces between the alternating membranes, and these spaces bound by two membranes are called cells. ED units consist of several hundred cells bound together with electrodes, and is referred to as a stack. Feed water passes through all the cells simultaneously to provide a continuous flow of desalinated water and a steady stream of concentrate (brine) from the stack.
ED and EDR are processes in which ions move through a semi-permeable membrane under the influence of an electrical current. In an EDR system the polarity, and by this the product and concentrate compartments, are reversed periodically in order to prevent scaling of the membranes.
ED is a suitable technology for the following cases:
- Treatment of water with a higher tendency to fouling or variable quality of feed water.
- High water recovery is required.
- High concentration of concentrate is required
Most common applications for ED are used in:
- Drinking water production
- Reuse water production
- Ground water nitrate removal
- Waste water concentration
- Food processing (whey, wine, sugar)
Example of EDR stack
REvivED water project aims to contribute to overcoming the drinking water challenge via novel desalination. The goal is to produce safe, affordable and cost-competitive drinking water with significantly reduced energy consumption compared to state-of-the-art Reverse Osmosis (RO) desalination technology. The project comprises several systems and applications with 12 pilots in total, ranging from Electrodialysis (ED) small systems for off-grid brackish water desalination in developing countries to larger scale hybrid (RED/ED-RO) systems for sea water desalination.
FUJIFILM coordinates the whole project as well as supplies ion-exchange membranes for all systems and components developed in the project.
FUJIFILM also leads development activities of the brackish water desalination systems as well as development and field-demonstration activities of the tap-water softening systems with a particular focus on designing, manufacturing and testing of the dedicated stacks.
The production of low-cost drinking water from sustainable resources is still the biggest challenge facing the world. Reverse Osmosis (RO) desalination is broadly used to produce drinking water. MIDES project introduces the Microbial Desalination Cell (MDC) as a pre-treatment for RO. The goal is to dramatically decrease the energy required for the drinking water production, to archive a high water recovery and to reduce waste.
The ion-exchange membrane (IEM) is a key successes factor in a good operation of the MDC. MDC requires IEM which has low electrical resistance and high perm-selectivity. The waste-water stream, entering the MDC, has a high fouling potential which may lead to decreasing of the MDC efficiency. Therefore, FUJIFILM focuses on development and manufacturing of a novel, anti-fouling IEM dedicated for MDC. The new membranes will be tested and used in three demonstration plants in Chile, Spain and Tunisia.