Different Ways of Chlorination: Gas, Liquid, and Solid Solutions

While the goal of chlorination remains the same—disinfection—the method of delivery varies significantly based on the scale of the operation, safety requirements, and cost. From massive municipal plants to backyard swimming pools, different forms of chlorine are utilized.

This guide breaks down the three primary methods of chlorination: Chlorine Gas, Sodium Hypochlorite, and Calcium Hypochlorite.

1. Chlorine Gas (Cl₂)

Form: Compressed greenish-yellow gas (liquefied under pressure).

• Application: Primarily used in very large municipal water treatment plants.
• Mechanism: When injected into water, it rapidly hydrolyzes to form hypochlorous acid (the killing agent).
• Pros: Cheapest form of chlorine per unit of disinfection power; 100% active chlorine.
• Cons: Extremely hazardous. A leak can be fatal. Requires highly specialized equipment, leak detectors, and safety training.

2. Sodium Hypochlorite (NaOCl)

Form: Pale yellow liquid (Liquid Bleach).

• Application: Widely used in medium-to-large water plants, industrial effluent treatment, and cooling towers. Also the standard for household bleach (though at lower concentrations).
• Mechanism: Delivered via dosing pumps directly into the water stream.
• Pros: Much safer to handle than gas; easy to automate with metering pumps.
• Cons: Degrades over time (shelf life issues); corrosive to pumps and piping; contains about 10-15% active chlorine (bulky to transport).

3. Calcium Hypochlorite (Ca(OCl)₂)

Form: White powder, granules, or tablets.

• Application: Remote water systems, swimming pools, emergency relief distribution, and "shock chlorination" of wells.
• Mechanism: Dissolved in a mixing tank or used in an erosion feeder.
• Pros: Stable solid (long shelf life); high concentration (65-70% active chlorine).
• Cons: Can cause calcium scaling (white residue) in hard water; creates a fire hazard if mixed with organic materials; requires manual handling to dissolve.

4. Chlorine Dioxide (ClO₂) and Chloramines

While not "chlorine" in the traditional sense, these related compounds are often grouped here:

• Chloramines: A mix of chlorine and ammonia. A weaker disinfectant but lasts much longer in pipes. Used for secondary disinfection in long distribution networks.
• Chlorine Dioxide: A potent gas generated on-site. excellent at destroying biofilms and doesn't form THMs (carcinogenic by-products), but is more expensive and complex.

Comparison Table