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Electrodialysis Calculator

Calculate electrodialysis stack current using Faraday law. Solve for current, flow rate, cell count, and efficiency.

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What is the Electrodialysis Calculator?

The Electrodialysis Calculator is a free online tool for designing and analyzing electrodialysis (ED) membrane systems. It uses Faraday's law to calculate the electrical current required for an ED stack based on solution normality, flow rate, removal efficiency, number of cell pairs, and current efficiency. You can also solve for flow rate, number of cells, current efficiency, normality, or removal efficiency.

This calculator is essential for environmental engineers, water treatment professionals, and chemical engineers working on brackish water desalination, food processing demineralization, pharmaceutical water purification, and industrial wastewater recovery.

How to Use the ED Stack Calculator

Select what you want to solve for from the dropdown menu. Enter the known parameters in your preferred units, and the calculator instantly computes the result with a detailed step-by-step breakdown of the formula. The Faraday constant (96,487 C/eq) is built into the calculation.

The tool can solve for current, flow rate, number of cell pairs, current efficiency, solution normality, or removal efficiency, making it a versatile design tool for electrodialysis systems of all scales.

Understanding the Electrodialysis Formula

The electrodialysis design equation relates the electrical current to feed properties and membrane stack geometry:

I = F × N × Q × E₁ / (n × E₂)

Where I is the electric current in amperes, F is Faraday's constant (96,487 C/eq), N is solution normality (eq/L), Q is volumetric flow rate (L/s), E₁ is removal efficiency (0 to 1), n is the number of cell pairs, and E₂ is current efficiency (0 to 1).

Applications of Electrodialysis

  • Brackish Water Desalination: Cost-effective salt removal for drinking water with TDS below 5,000 mg/L
  • Food and Beverage Processing: Demineralizing whey, wine, and fruit juice without thermal damage
  • Pharmaceutical Manufacturing: Producing purified water and removing ionic impurities from drug formulations
  • Industrial Wastewater: Recovering valuable ions like lithium, copper, and nickel from process streams
  • Table Salt Production: Concentrating seawater brine before evaporation

Frequently Asked Questions

How does electrodialysis remove salt from water?

ED applies a DC voltage across a stack of alternating cation-exchange and anion-exchange membranes. Dissolved ions migrate through the selective membranes toward the electrodes, concentrating in reject channels and leaving purified water in the product channels. No high pressure is needed, unlike reverse osmosis.

When is electrodialysis preferred over reverse osmosis?

ED is generally preferred for brackish water below 5,000 mg/L TDS where it uses less energy than RO. ED is also better when selective ion removal is needed (e.g., nitrate removal while keeping calcium), when the feed has high fouling potential, or when brine recovery is important.

What is Faraday's constant and why does it appear in the ED equation?

Faraday's constant (F = 96,487 C/eq) is the electric charge carried by one mole of monovalent ions. It converts the chemical demand (equivalents of ions to remove per second) into the electrical demand (amperes of current) that the stack must supply.

What is a typical current efficiency for an ED stack?

Current efficiency typically ranges from 0.80 to 0.95. Losses come from back-diffusion of ions, water transport through the membranes, and electrical leakage between cells. Well-maintained stacks with tight seals usually exceed 0.90.

How many cell pairs does a commercial ED stack typically have?

Small laboratory or pilot stacks may have 10-50 cell pairs, while full-scale commercial stacks typically contain 200-600 cell pairs. The number depends on the target ion removal, available current, and space constraints.

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