Electrocoagulation: Treating Water with Electricity
Electrocoagulation (EC) is an emerging technology that uses electrical current to remove contaminants like oil, emulsions, and heavy metals without adding consumable chemicals.
Traditional Coagulation involves buying truckloads of chemicals (Alum, Ferric Chloride) and dumping them into the water. Electrocoagulation (EC) achieves the same result using only electricity and metal plates.
The Process
An EC reactor consists of full metal plates (Electrodes) submerged in the dirty water.
- Anode (+): Usually made of Iron or Aluminum. As electricity flows, this metal "sacrifices" itself, dissolving metal ions (Fe2+ or Al3+) into the water. These act exactly like the chemicals Alum or Ferric Chloride.
- Cathode (-): Water splits here to release Hydrogen gas bubbles.
The "Triple Action" of EC
- Coagulation: The dissolved metal ions neutralize the charges of dirt and oil, causing them to clump.
- Flotation: The tiny hydrogen bubbles produced at the cathode stick to the oil/dirt clumps and float them to the surface (Skimming).
- Oxidation: The electrical current can break down complex organic molecules and dyes directly.
Best Applications
EC is not cheap (electricity costs), so it is used where chemicals fail.
- Oily Wastewater: Car washes, mechanical workshops. EC is brilliant at breaking stable oil-water emulsions.
- Textile Dyeing: It removes color very effectively.
- Heavy Metals: Chrome plating, battery manufacturing.
Pros vs Cons (Chemical vs Electrical)
| Feature | Chemical Coagulation (Alum/Lime) | Electrocoagulation (EC) |
|---|---|---|
| Sludge Volume | High (Chemicals add to volume) | Very Low (Only pollutant settles) |
| TDS Increase | Increases salinity (Anions like Sulfate/Chloride) | Minimal increase |
| Handling | Hazardous acid/alkali storage | Safe metal plates |
| Cost | Low OpEx | Higher OpEx (Power + Plates) |
| Best For | Large flows (Sewage/River Water) | Complex flows (Oil/Dye/Ink) |
The Challenge: Passivation
The #1 reason EC plants fail is Passivation.
- What is it? An insulating oxide layer ("Rust") forms on the Anode. This layer blocks the electricity. The voltage rises, but no current flows. The treatment stops.
- Solution:
- Polarity Reversal: Modern EC control panels automatically flip the Plus (+) and Minus (-) every 15 minutes. This makes the cathode an anode, stripping off the scale.
- Acid Wash: Periodically dipping plates in dilute HCl to clean them.
The Math: Electrode Consumption
How much metal do you lose? We use Faraday's Law.
m = (I * t * M) / (z * F)Where:
- I = Current (Amps)
- t = Time (seconds)
- M = Molecular weight (Aluminum = 26.98)
- z = Valency (3)
- F = Constant (96,485)
Rough Rule of Thumb: To treat 1 m³ of dirty water, you might consume 0.05 to 0.1 kg of metal electrode.
Maintenance Checklist
- Daily: Check Amperage. If Amps drop but Voltage stays same, clean the plates.
- Weekly: Inspect connections. High current melts loose wires.
- Monthly: Lift the plate pack. Power wash the sludge trapped between plates.
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