What are the pros and cons of each of the three forms of chlorine (chlorine gas, sodium hypochlorite, calcium hypochlorite) used for drinking water disinfection?
Disinfection with chlorine is simple, economical, efficient, measurable, and practical. Gaseous chlorine is by far the most common form of chlorine used in water system disinfection, however, it is a hazardous, corrosive gas, and special precautions must be taken to ensure safety. Sodium hypochlorite is an aqueous solution and often referred to as liquid bleach or Javelle water. This form of chlorine is more likely to be used by small systems because it generally requires less equipment, is easier to use, and safer than chlorine gas. Calcium hypochlorite is a solid crystal, often added to drinking water as a dilute hypochlorite solution. Like Sodium hypochlorite, it requires less equipment, is easier to use, and safer than chlorine gas. However, calcium hypochlorite is highly reactive to heat and moisture, and must be stored in a cool, dry place. (Occurrence Assessments for the Final Stage 2 Disinfectants and Disinfection Byproducts Rule, EPA815-R-05-011)
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