Chloramine is especially effective in the distribution system pipes and is formed by adding ammonia to the water which contains free chlorine. If used in excess of its maximum residual disinfectant level, it may cause irritation of the eyes, nose, and stomach, or anemia in some people.

Chlorine is added either as a gas or liquid. It is the cheapest of the disinfectants and has a long history of being effective on most microorganisms. If used in excess of its maximum r esidual disinfectant level, it will cause irritation of the eyes, nose, and stomach for some people.

Chlorine dioxide is very effective in treating the potable water supply and disappears from the water rapidly. The four main ways of producing chlorine dioxide are electrochemical, the acid- chlorite method, the chlorine-chlorite method, and three chemical processes. (See endnote 26 for specific reactions during the production of the chlorine dioxide.) If used in excess of the maximum residual disinfectant level, some infants, young children, and fetuses will suffer from nervous system problems. Drinking excessive amounts of the chlorine dioxide in water over several years may cause anemia. The National Primary Drinking Water Standards for the three disinfectants are chloramine 4 ppm, chlorine 4 ppm, and chlorine dioxide 800 ppb.

Ozone is an extremely strong oxidant and disinfectant utilized in water treatment systems. It works much faster than chlorine, inactivates viruses, oxidizes organic and inorganic compounds, removes iron and manganese, and controls taste and odors. It is used in many water treatment facilities. It is used for control of MS-2, poliovirus, Giardia cysts, and Cryptosporidium. The disadvantages are the higher cost of equipment and operation, water hardness may affect the process, potential fire hazards, and toxicity problems for people. Also there is no carryover of a disinfectant residual and therefore chlorine has to be used afterwards to prevent growth of microorganisms. Some of the ozone byproducts and reactions with chemicals in the water may include brominated compounds, aldehydes, ketones, and carboxylic acids and these may have serious health effects. (See endnote 27.)

Ultraviolet light may be used for disinfection at the proper wavelength which has germicidal properties (200-300 nm). Some of the problems include breakage of the lamp which could release mercury into the water; the use of a UV reactor which may alter the dose delivery rate and time, and therefore not affect all microorganisms; UV light inactivates the organism but does not destroy it; the proximity of the water to the UV light and how clean the light is kept affects the process; and the amount of turbidity present.

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