Treatment process
Electrodialysis
Uses an electric field to pull ions through selective membranes, rather than pushing water through a membrane. Most efficient on brackish water of low to moderate salinity.
Key facts
- Scale
- Industrial / large scale
- Treatment stage
- Membrane separation
How it works
Alternating cation- and anion-selective membranes sit between electrodes. The applied field draws ions into alternate channels, producing a diluted stream and a concentrated one. Reversing polarity periodically controls scaling.
What it removes — and what it does not
| Row | Removes | Does not remove |
|---|---|---|
| 1 | Dissolved ionic species — salts, nitrate, fluoride | Uncharged species: bacteria, viruses, most organics, silica |
Trade-offs
- Energy scales with the salt removed, so it is efficient for low salinity and uneconomic for seawater
- Membranes tolerate chlorine better than RO membranes
- Reversal operation gives good scaling resistance
Related intelligence
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Sources
- World Health Organization — Guidelines for Drinking-water Quality. Public but restricted · CC BY-NC-SA 3.0 IGO
- NSF International / American National Standards Institute — NSF/ANSI drinking water treatment unit standards. Public but restricted · Publisher terms — public access, reuse not clearly granted
- American Water Works Association — AWWA standards, water audits and utility benchmarking. Public but restricted · Publisher terms — public access, reuse not clearly granted