Calcium hypochlorite (Ca(OCl)2) is essentially a solid that is used in place of liquid NaOCl.
As a mixture with lime and calcium chloride, Calcium Hypochlrite is marketed as chlorine powder or bleach powder for water treatment and as a bleaching agent.
In addition to water treatment, Calcium hypochlorite is used in kitchens to disinfect surfaces and equipment. Other common uses include bathroom cleansers, household disinfectant sprays, algaecides, herbicides, and laundry detergents.
Calcium Hypochlorite; Advantages
This compound is relatively stable, is similar to sodium hypochlorite in disinfection properties and has greater available chlorine than sodium hypochlorite (liquid bleach).
It has excellent stability when kept in dry storage, maintaining its potency over time. Commercial grades of Ca(OCl)2 generally contain about 70% available chlorine making it appropriate for both drinking water and wastewater applications.
Calcium Hypochlorite is appropriate for both drinking water and wastewater applications.
Calcium Hypochlorite; Disadvantages
Because the chemistry is so similar to chlorine gas and NaOCl (“liquid chlorine”), this method offers no disinfection efficiency advantages (i.e., Giardia and Cryptosporidium kill rates) nor disinfection by-product advantages.
Although solid Ca(OCl)2 is more stable and safer to handle than its liquid counterpart NaOCl, it is corrosive and hygroscopic (i.e., readily absorbs moisture), reacting slowly with moisture in the air to form chlorine gas if not stored in air-tight containers.
Therefore, containers of Ca(OCl)2 must be completely sealed or emptied entirely. As with chlorine gas and NaOCl, wastewater systems using Ca(OCl)2 generally require dechlorination after disinfection to reduce chlorine discharges to receiving waters.
Source: Disinfection Technologies for Potable Water and Wastewater Treatment:
Prepared by: Leslie Snowden-Swan, John Piatt, Ann Lesperance - Pacific Northwest National Laboratory