EDM – ED Metathesis
For high brine concentration applications without scaling risk
Membranes: standard grade, monovalent grade homogeneous anion and cation exchange membranes
How does it work?
EDM like 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.
ED and EDM are processes in which ions move through a semi-permeable membrane under the influence of an electrical current. In an ED and EDM system the polarity, and by this the product and concentrate compartments, are reversed periodically in order to prevent scaling of the membranes.
The difference between ED and EDM is made by making use of standard grade and monovalent membranes and the way cell pairs are configured. Where ED works with 2 membrane types in 1 cell pair, EDM works with 4 membrane types in 1 cell pair.
When one want to achieve high concentration rates above 10-15% with regular ED processes, the risk for scaling increases. The multi valent ions such as sulphates, carbonates, phosphates intend to scale with the magnesium or calcium when moving to higher concentration rates.
EDM Stacks use a special cell pair configuration making using of standard grade (AEM, CEM) and monovalent grades (AEM mono, CEM mono) membranes which ensure that the magnesium, calcium and the multivalent anions are concentrated up in different compartments.
This results into the following advantages compared to regular ED process:
- Brine concentration of (SW, BW or process water) feed-in streams into two (2) separated brine streams (Ca/Mg rich & SO4 rich) without scaling.
- DRW desalination (from SW/BW) within same process step.
- Salt production
- Industrial process streams
- Brackish / seawater RO brine
Example of EDM stack
Zero Liquid Discharge desalination: brine treatment based on electrodialysis metathesis and valuable compound recovery. EDM Technology is used in the ZELDA Research project.