Electrodialysis Reversal (EDR) & ZLD Lab

Model electrochemical ion transport, alternating CEM/AEM membrane stacks, polarity reversal self-cleaning, and Zero Liquid Discharge (ZLD) brine concentration economics.

Presets:
Net LCOT ($/m³)
-$0.12 (Net Sav)
Net cost per m³ feed treated
Specific Energy
2.45 kWh/m³
Feed SEC (DC + aux pump)
Avoided ZLD Brine
309 k m³/yr
Diverted from crystallizers
Facility CapEx
$5.75M
Stacks, rectifiers, skids

Feedstock & Electrochemical Parameters

Feed Wastewater Flow (m³/day): 5,000 m³/d
Feed Salinity (ppm TDS): 15,000 ppm
EDR readily treats high-silica, high-calcium brines up to 50k ppm where RO scales rapidly.
Target Product Salinity (ppm TDS): 450 ppm
Water Recovery Ratio (%): 88 %
Concentrates residual brine up to 120,000–160,000 ppm TDS without membrane damage.

Energy, CapEx & ZLD Credits

Electricity Tariff ($/MWh): $55
Avoided Thermal Crystallizer Cost ($/m³): $35
Thermal MVR crystallizers cost $30–$70/m³ in steam and power; EDR avoids ~80% of this brine volume.
Installed CapEx ($/m³·day capacity): $1,150

Cost Stack Breakdown ($/m³ Feed)

  • DC Power & Aux Pumping: $0.135
  • CEM / AEM Membrane Replacement: $0.045
  • Electrodes & Reversal Actuators: $0.025
  • Chemicals (Low Due to EDR Reversal): $0.018
  • Labor & Operating Overhead: $0.071
  • Gross Operating Cost (OpEx): $0.294
  • Annualized Capital Amortization: $0.065
  • ZLD Crystallizer Savings + Water Credit: -$0.471
  • Net Levelized Cost of Treatment: -$0.12
EDR Membrane Stack & Polarity Reversal Circuit Self-Cleaning EDR
FEEDWATER SALINITY 15,000 ppm CONCENTRATED BRINE 121,708 ppm WATER RECOVERY RATIO 88 % SPECIFIC ENERGY (FEED) 2.45 kWh/m³ CONNECTED DC LOAD 0.51 MW POLARITY REVERSAL CONTROLLER Cycle: 20 min interval (Auto-Descaling) (+) ANODE (-) CATHODE CEM AEM CEM AEM CEM AEM Dilute Brine Dilute Brine MOTORIZED 4-WAY REVERSAL MANIFOLD Stream swap synchronizer CLEAN WATER TDS < 500 ppm Reuse in Process ZLD MVR 80% Vol Avoided ► BRACKISH FEED
Net Present Value
$22.4M
20-year @ 7.5% WACC
Internal Rate of Return
38.5%
Driven by ZLD avoidance
Simple Payback
2.4 yrs
Rapid capital payback

5x5 Sensitivity Matrix: Net Levelized Cost of Treatment ($/m³ Feed)

Feed Salinity vs Crystallizer Avoidance Value
Salinity \ ZLD Value $15/m³ $25/m³ $35/m³ $45/m³ $60/m³

20-Year Project Pro-Forma Snapshot

Period Total Benefit Total OpEx EBITDA Net Cash Flow Cumulative Cash

Mastery Assessment: Electrodialysis Reversal Principles

1. What physical force drives ion transport in an electrodialysis stack?
2. How does the periodic polarity reversal mechanism prevent mineral scaling (e.g. CaSO4, BaSO4, silica)?
3. Why does inserting an EDR system upstream of a Zero Liquid Discharge (ZLD) thermal crystallizer yield high project returns?
4. How does EDR energy consumption scale compared to pressure-driven reverse osmosis (RO)?

Frequently Asked Questions

Electrodialysis Reversal is an electrochemical membrane separation process that uses a direct current (DC) electric field to pull dissolved ions (cations like Na+, Ca2+, and anions like Cl-, SO4(2-)) across alternating ion-exchange membranes (cation exchange membranes [CEM] and anion exchange membranes [AEM]). The alternating arrangement creates alternating dilute (purified freshwater) and concentrate (brine) channels without requiring high hydraulic pressures.

Every 15 to 30 minutes, the DC electrical polarity across the membrane stack is automatically reversed (the anode becomes the cathode and vice versa), while motorized valve manifolds simultaneously swap the dilute and concentrate flow streams. This immediate reversal repels polarizing ions and dissolves precipitating mineral scale (such as calcium sulfate and silica) that began forming on the membrane surfaces, eliminating the need for continuous acid or antiscalant chemical dosing.

Zero Liquid Discharge systems eliminate all liquid wastewater discharge, typically ending in energy-intensive mechanical vapor recompression (MVR) evaporators and crystallizers ($40 to $90/m³). When placed between reverse osmosis and the crystallizer, EDR concentrates the brine from 60,000 ppm up to 150,000+ ppm TDS at 85% to 92% recovery, slashing the residual wastewater volume sent to the thermal crystallizer by 80% and drastically reducing facility CapEx and OpEx.

In reverse osmosis, energy consumption is proportional to the total volume of water pumped across the hydraulic membrane barrier. In electrodialysis, electrical energy consumption is directly proportional to the mass of ions removed (Faraday's law: E = I · V · t). For low-to-medium salinity waters (2,000 to 10,000 ppm TDS) and high-salinity brine concentration where RO osmotic pressure exceeds membrane burst limits, EDR delivers lower or competitive specific energy consumption (1.2 to 3.5 kWh/m³).

EDR is widely deployed in semiconductor manufacturing (ultra-pure water recovery), power generation cooling tower blowdown, flue-gas desulfurization (FGD) wastewater, mining drainage and tailings reclamation, petrochemical refineries, and inland municipal brackish aquifer desalination where silica scaling and brine disposal are restrictive bottlenecks.

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