- 2025-07-22
Removal of chlorine from water
Chlorine disinfection mechanism and risks
Chlorine (Cl₂) and hypochlorite (such as NaOCl/Ca(OCl)₂) generate hypochlorous acid (HOCl) through hydrolysis:
NaOCl + H₂O → HOCl + NaOH
Ca(OCl)₂ + 2H₂O → 2HOCl + Ca(OH)₂
HOCl penetrates the cell wall of microorganisms and inactivates them, effectively controlling pathogens such as Vibrio cholerae (inactivation rate > 99.99%).
Residual chlorine hazards:
Drinking water: Chlorophenol odor is generated when free chlorine is greater than 0.5mg/L (odor threshold 0.02mg/L)
Industrial system: Cl⁻ reacts with iron pipes to generate FeCl₂ (corrosion rate > 1mm/year)
Health risks: Long-term exposure to chloroform (THMs) carcinogens (GB 5749 limit < 0.06mg/L)
Engineering-grade dechlorination solution
Activated carbon adsorption system
Material selection: coconut shell charcoal (iodine value ≥ 1000mg/g)
Adsorption capacity: 1g charcoal can remove 3-6mg residual chlorine
Empty bed contact time (EBCT) ≥ 6 minutes
Advantages: No power consumption, simultaneous removal of organic matter (TOC removal rate > 70%)
Chemical reduction dechlorination
Agent type Reaction equation Dosage ratio (Cl₂:agent)
Sulfur dioxide SO₂ + HOCl → H₂SO₄ + HCl 1:0.9
Sodium metabisulfite Na₂S₂O₅ + 2HOCl → 2NaHSO₄ + HCl 1:1.34
Sodium bisulfite NaHSO₃ + HOCl → NaHSO₄ + HCl 1:1.46
Process combination application
Beverage production line: activated carbon filtration (residual chlorine <0.05mg/L) → reverse osmosis system
Wastewater treatment plant: sulfur dioxide dechlorination (residual chlorine in effluent <0.02mg/L) → Ecological discharge
Seawater desalination: double alternating carbon filter system (continuous operation cycle > 8000 hours)
Key equipment selection
Canister carbon filter: FRP material, design flow rate 8-12m/h
Chemical dosing device: diaphragm metering pump (accuracy ±1%), ORP online control
Dual filter bed system: automatic valve group switching to ensure continuous water supply
Industry application value
Safe water supply: eliminate the risk of THMs generation (Ames test negative)
Equipment protection: carbon steel pipeline life extended to more than 15 years
Production optimization: beverage factory flavor complaint rate decreased by 90%
Ecological safety: discharge water fish acute toxicity (LC50) > 100mg/L
