Reverse osmosis
Pressure forces water through a semi-permeable membrane and leaves the dissolved solids behind. Rejection is by size and charge, not identity, so everything goes — including the calcium and magnesium. It needs 25–35 bar to do it.
Comparison
Electrodialysis vs reverse osmosis for high-recovery brackish water treatment.
Both desalinate. They differ in how much of the feed you keep, how much brine you have to get rid of, and whether the minerals survive the process. On a difficult inland source those three things usually decide the project.
Every figure below comes from one completed pilot — Chemical plant, Germany, industrial cooling water (90-day pilot, 2023), Feb–May 2023, a 90-day head-to-head against RO and standard EDR on the same feed water at 4.5 g/L TDS and silica 85 mg/l. A different feed water will give different numbers.
Compare against your own water
Send the analysis and we will tell you which process fits — including when it is not ours.
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How they differ
One rejects everything. The other moves selected ions.
Electrodialysis reversal
An electric potential pulls selected ions through ion-exchange membranes and out of the product stream. Transport is driven by charge, so the process can be configured to remove some ions and retain others, at 0.5–2.5 bar.
Head to head
Brine minimisation, energy and cost.
Measured on one feed water over 90 days. Conditions are stated so the numbers can be checked against your own source.
| Parameter | SonixED™ | Reverse osmosis | Standard EDR |
|---|---|---|---|
| Water recovery | 90–98% | 50–75% | 70–85% |
| Energy consumption | 0.19–0.7 kWh/m³ | 2.0–4.0 kWh/m³ | 1.0–2.0 kWh/m³ |
| Operating pressure | 0.5–2.5 bar | 25–35 bar | 1–2 bar |
| Chemical dosing | Minimal — no anti-scalant | Required | Anti-scalants needed |
| CIP cleaning frequency | 0.6×/month | 1×/month | 1×/month |
| Annual discharge reduction | 43,680 m³/yr | 26,880 m³/yr | 34,176 m³/yr |
| Total treatment cost | $0.30–0.40/m³ | $0.60–1.00/m³ | $0.40–0.80/m³ |
Source: Chemical plant, Germany — industrial cooling water (90-day pilot, 2023). One feed water (4.5 g/L, high silica). Results on your water depend on feed salinity. Download the full case study →
What the numbers mean
Where the difference actually lands.
Recovery decides the brine
Recovery and brine volume are the same number seen from either end. Moving from the RO range to the SonixED™ range is what turns disposal from a project-ending cost into a manageable one, which is the whole of brine minimisation.
Pressure decides the energy
RO needs high pressure because it pushes water through a barrier. Electrodialysis moves ions instead, so it runs an order of magnitude lower and the energy figures follow from that rather than from a better pump.
Scaling decides whether it keeps running
Anti-scalant dosing is the usual answer to hard, silica-laden water. Ultrasound-assisted scaling control removes that consumable, which is why the CIP frequency differs rather than the membrane being better.
Honest limits
When reverse osmosis is the better answer.
Choose RO
Not our use case: seawater (~35 g/L), where SWRO is typically preferred. Sources where full demineralisation is genuinely the objective. Applications needing removal of organics or pathogens, which an ion-selective process does not address.
Choose selective electrodialysis
Brackish sources in the 1–20 g/L TDS range. High silica or high hardness that fouls membranes. Inland sites with no discharge route. Cases where the minerals should stay in the water.
We tell you which of these applies to your source, including when it is the first one. See selective nitrate removal → or groundwater desalination →
Engineering Assessment
Send the water data. We assess the fit.
TDS, hardness, silica, target flow and discharge constraints are enough to start.
