How it works
- resin that self-regenerates — An EDI cell is packed with mixed-bed resin between an anion and a cation membrane. Ions are exchanged onto the resin exactly as in IX — but a DC field then drags them off the resin, through the membranes, and into an adjacent concentrate channel. No brine, no regeneration outage.
- water splitting — At the resin-to-resin contact points the field splits water into H⁺ and OH⁻. Those are the regenerant: they continuously strip the resin back to its free form. The regeneration chemistry is generated in situ from the water itself.
- the current balance — Current must at least match the ionic load — one Faraday per equivalent, about 26.8 amp-hours. Too little and ions break through. Too much and you drive polarisation: excess water splitting, pH excursions and hardness scaling on the concentrate side.
- why RO comes first — EDI needs a feed already below about 40 µS/cm and essentially free of hardness — which means RO permeate. Feed CO₂ matters more than people expect: it is not rejected by RO, ionises inside the stack, and consumes current that should be removing salt.
- what governs it — Ionic load sets the current; current sets the product quality and the power; excess current sets the scaling risk. Wind CO₂ up and watch the current requirement climb — degassing upstream is often cheaper than a bigger stack.
Design parameters
The panel opposite runs the same correlations as the CDI-650 design sheet, so the animation and the calculator cannot disagree. Drag any of them and the picture responds.
- Product flow — m³/h
- Feed conductivity — µS/cm
- Feed CO₂ — mg/L
- Stack current — A
- Stack voltage — V
- Recovery — %
Open the full CDI-650 design sheet for the governing equations, the accepted design envelopes and the worked calculation.