Calcium Hypochlorite
The most common source of chlorine used in post-harvest chlorination is calcium
hypochlorite. It is available commercially in the form of either a granulated powder or
large tablets. Most commercial formulations are 65 percent calcium hypochlorite, with the
balance consisting of stabilizers and inert materials. Calcium hypochlorite is relatively
stable as long as it is kept dry, and it may be stored for extended periods. The property that
makes it stable also makes it difficult to dissolve completely in water. Adding granulated
Sodium Hypochlorite
The active ingredient of most liquid household bleaches; sodium hypochlorite is
commonly used when the scale of post-harvest chlorination is limited. Sodium
hypochlorite is not generally available in solid form because it is difficult to store. It
absorbs moisture readily from the atmosphere, causing it to release chlorine gas.
Household bleach is usually marketed as a solution of water and 5.25 percent sodium
hypochlorite. Larger containers of 12.75 percent or 15 percent sodium hypochlorite
solutions are also available through some laundry and swimming pool chemical suppliers.
For the same amount of chlorination, a sodium hypochlorite solution is generally more
expensive than granular calcium hypochlorite because of the additional shipping and
handling costs associated with the water it contains.
Chlorination chemicals can be added to the water manually, or concentrated solutions of
sodium or calcium hypochlorite can be injected into the wash tank or hydrocooler at a
continuous and measured rate. Commercial chlorine injector systems are particularly
useful in operations where a continuous supply of clean, chlorinated water is required.