In recent years Electro Dialysis (ED) has taken a new direction in system design, giving the technique unprecedented capability in desalination and industrial wastewater recovery.
However, the basic operating principle is still the same. Since its introduction in the 1950s, Electro Dialysis has used a DC electrical potential and selectively permeable membranes (permeable to same-charge ions but relatively impermeable to opposite-charge ions and water) to remove ionized materials from aqueous solutions.
In seawater and brackish water desalination applications ED was previously considered too energy-intensive to compete with reverse osmosis (RO). But ED requires less extensive feed water pretreatment than a pressure-driven membrane process, such as RO and Nanofiltration and it also answers the increasing needs of recycling and conservation.
Another important feature, the incorporation of periodic reversal of electrode polarity (EDR), has made the process more tolerant of difficult feed water conditions. By reducing pre-treatment requirements (acid and anti-scaling treatments), polarity reversal has made EDR even more competitive with RO.
Electrodialysis (ED) and Electrodialysis Reversal (EDR) modules can produce a high recovery rate of reverse osmosis (RO) reject water, without membrane fouling and scaling problems. It was once cost-prohibitive to use electrodialysis in this role but the new technology follows a decade of research and development that has removed the problem. Today’s new generation Electrodialysis modules have a cross-flow fluid path, high performance membranes and lower cost control technology. Modulating the applied DC power also allows tuning of the process to select a desired quantity of salt removal.
The advantage of EDR over ED is that a periodic reversal of electrode polarity produces the equivalent of backwashing of the Electrodialysis membrane, which also reduces anti-scaling pre-treatment requirements. The EDR modules have already been used to increase the overall RO recovery to 96% (out of basic 50 – 70%)
