Comparison of Chlorine-Based Water Treatment Methods

1️⃣ Chlorine Dioxide (ClO₂)

🧪 Production Method

ClO₂ is produced on-site through a chemical reaction between sodium chlorite (NaClO₂) and an acid (HCl or H₂SO₄).

⚙️ Required Chemicals and Equipment

• Sodium chlorite solution (25%)

• Acid (HCl or H₂SO₄)

• ClO₂ generator (mixing chamber, gas exhaust, dual dosing)

✅ Advantages

• Highly effective against biofilm, algae, bacteria, viruses

• No THM/AOX formation

• Low dosage required, wide pH range

❌ Disadvantages

• High operating costs (OPEX) and medium to high investment costs (CAPEX)

• Explosion risk at high concentrations

• Formation of chlorite and chlorate

☢️ By-products

• Production: NaCl (salt)

• Use: Chlorite (ClO₂⁻), chlorate (ClO₃⁻)

🏭 Examples

• ProMinent, Grundfos, Siemens OSEC

2️⃣ Sodium Hypochlorite (NaOCl)

🧪 Production Method

Industrial production by reacting chlorine gas with sodium hydroxide.

⚙️ Required Chemicals and Equipment

• Purchased NaOCl solution

• Storage tank, dosing pump, optional control system

✅ Advantages

• Inexpensive, simple application

• Well-known technology

❌ Disadvantages

• Unstable over time in storage

• Forms THM and AOX in the presence of organics

• Adds salt to the system

• pH-sensitive

☢️ By-products

• THMs (e.g., chloroform), AOX, Na⁺ and Cl⁻ ions

🏭 Examples

• Hayward, Kemira, Javel

3️⃣ Chlorine Gas via Membrane Electrolysis (Cl₂ in situ)

🧪 Production Method

Electrolysis of brine (NaCl solution) generates Cl₂ and NaOH.

⚙️ Required Chemicals and Equipment

• Salt + demineralized water

• Electrolysis unit

• Hydrogen gas exhaust and safety systems

• Dosing and pH control

✅ Advantages

• No chemical storage required

• Low operating cost

• Consistent, pure production

• Environmentally friendlier (on-site production)

❌ Disadvantages

• High CAPEX

• Hydrogen gas safety risk

• Salt accumulation in recirculation systems

☢️ By-products

• H₂ gas, NaOH, THMs, AOX

🏭 Examples

• Aguabel, Evoqua, De Nora

4️⃣ Stabilized Hypochlorous Acid (HOCl)

🧪 Production Method

Electrochemical production from water, salt, and acid, stabilized at pH 5.5–6.5.

⚙️ Required Chemicals and Equipment

• Demineralized water, salt, acid or HOCl generator

✅ Advantages

• High antimicrobial effectiveness

• Low corrosion risk

• No THM or AOX formation

• Safe for plants

❌ Disadvantages

• Limited stability over time

• Relatively new, less field experience

• Moderate OPEX

☢️ By-products

• Minimal salt residues

🏭 Examples

• EcoloxTech, Decon7, Clarion Water

📊 Summary Table: