Chlorination is similar in many ways to iodination of drinking water. Like iodine, chlorine treatment can be used to inactivate bacteria, viruses, and some protozoa. However, at the low levels of chlorine typically used for drinking water treatment, giardia spores will not be inactivated. Chlorine concentrations of 10 mg/L must be maintained for 30 minutes in order to inactivate giardia (Extension Bulletin 795, 2003). A number of variables influence the amount of chlorine necessary for disinfection. These include PH, water temperature, and turbidity (Extension Bulletin 795, 2003). Longland gives a thorough explanation of tests that can be conducted in order to determine the chlorine demand in a given water supply (Longland,
Six drops of ordinary household bleach (5.25 % free chlorine) is sufficient to disinfect each gallon of drinking water. The water must be shaken and kept in contact with bleach for thirty minutes. Industrial bleach (15 % free chlorine) and dry bleach (4% free chlorine) contain different concentrations of chlorine and calculations need to be made in order to determine the appropriate amount to be added per gallon of water (National Center for Environmental Health, 2003).
On a larger scale, either more chlorine can be added manually, or a chlorinator can be installed in order to constantly deliver an appropriate concentration of chlorine to the water supply. Like the iodinator, this will require materials and relevant expertise to install.
Also like iodine, the adverse health effects associated with chorine are ill defined. “The adverse affects of chlorination result both from chlorine and from compounds formed by the reactions of chlorine with other chemicals present in water”(Garfield, 1985). Although adverse health effects associated with chlorine disinfection are proven, it is still amongst the best technologies available in the developed world. The promise of chlorination in the developing world is therefore also great, considering the low cost of bleach. Nonetheless, alternatives should be constantly considered to reduce the potential for adverse health effects related to chlorine disinfection.
Due to the complex nature of advanced chlorinating systems, they will not be discussed in detail here. Links and resources related to the chemistry, design, and construction of chlorine disinfection systems are provided below:
General information about small-scale chlorination: