Salt concentration reduction in electrodialysis
Electrodialysis moves ions through selective membranes under an electric potential, producing a dilute stream and a concentrate stream. Comparing feed and dilute-product concentration gives a simple concentration-reduction percentage.
Concentration reduction is not the same as salt mass removal, water recovery, current efficiency, membrane selectivity, or energy efficiency. Those metrics require flow rates, concentrate data, electrical measurements, and a defined mass balance.
How to use the salt removal calculator
- Enter feed concentration: Use a positive salinity or target-ion concentration.
- Enter product concentration: Use the same unit and analytical basis as the feed.
- Calculate reduction: Review the relative concentration decrease.
- Complete the process balance: Use flow, concentrate, recovery, current, voltage, and ion data for actual system performance.
Formula and variables
Both concentrations must use the same unit, analytical basis, and salt-equivalent definition.
Concentration reduction = (Cfeed − Cproduct)/Cfeed × 100%- Cfeed — Feed concentration
- Salt concentration entering the process
- Cproduct — Product concentration
- Salt concentration in the dilute product stream
Feed-to-product concentration example
Feed concentration is 1,000 mg/L and dilute product concentration is 100 mg/L.
- Feed
- 1,000 mg/L
- Product
- 100 mg/L
- Reduction = (1,000 − 100)/1,000 × 100%
- Reduction = 90%
Result: Salt concentration is reduced by 90%.
This alone does not reveal how much total salt was transferred or how much energy and water were used.
Understanding your results
Do not call this overall process efficiency
The ratio only compares concentrations in two streams.
- Water recovery can change concentration independently of salt transfer.
- Mass removal requires concentration multiplied by flow.
- Current efficiency requires ionic charge and electrical-current data.
- Specific energy requires electrical energy per treated-water volume.
Assumptions
- Feed and product concentrations are measured consistently.
- Product concentration does not exceed feed concentration for the selected reduction calculation.
- The values represent comparable stream conditions.
Limitations
- Does not calculate mass balance, flow recovery, concentrate concentration, current efficiency, membrane area, limiting current, stack voltage, or energy use.
- Does not model ion-specific transport, water transport, fouling, scaling, leakage, or electrode reactions.
- Not a design or regulatory water-quality tool.
Common mistakes
- Mixing conductivity with concentration without a calibration.
- Using different concentration units or salt bases.
- Calling concentration reduction mass-removal efficiency.
- Ignoring flow-rate changes between feed and product.
Practical use cases
Treatment reporting checks
Verify a stated feed-to-product concentration reduction.
Desalination education
Distinguish concentration reduction from recovery and electrical efficiency.
Frequently asked questions
Is 90% concentration reduction the same as 90% salt mass removal?
Not necessarily. Salt mass flow also depends on stream flow rate.
Can I use conductivity values?
Only as a relative surrogate when both measurements are comparable; conductivity-to-salinity relationships depend on ionic composition and temperature.
Does this calculate electrodialysis energy use?
No. Voltage, current, operating time, and treated-water volume are required.
Sources and review
- Seawater Desalination Bandwidth Study — U.S. Department of Energy. Accessed 2026-07-13.
Reviewed 2026-07-13.