Chlorine

Applied as gas or liquid (hypochlorite)

·         Effective for most microorganisms

·         Can oxidize  iron and manganese (makes them easier to remove)

·         Keeps a residual in distribution system

·         Technology well understood

·         Relatively easy to use in hypochlorite form

·         Forms DBPs when organic substances are present

·         Not effective against Cryptosporidium protozoa

·         Can cause  taste and odor problems

Chloramines

Formed by combining chlorine and ammonia

·         Forms more stable residual than chlorine alone

·         Forms less DBPs than chlorine

·         Forms less taste and odor causing compounds in water

·         Technology well understood

·         Less effective than chlorine against microorganisms, especially viruses and protozoa

·         Poorly oxidizes iron and manganese

·         Usually requires a more powerful disinfectant for primary disinfection

Chlorine Dioxide

Produced by reacting sodium chlorite with chlorine or hydrochloric acid

·         More effective than chlorine or chloramines as disinfectant against microorganisms

·         Controls taste and odor better than chlorine  in some cases

·         Forms less THMs* and HAAs* than chlorine

·         Must be produced on site

·         Forms additional DBPs such as chlorite and chlorate

·         Requires daily chlorite and chlorine dioxide monitoring 

·         Costs more for equipment and chemicals than chlorine

·         Takes more technical skill to use

Ozone

Produced by electrical discharge through air or oxygen

·         Most powerful disinfectant used in drinking water treatment

·         More effective than chlorine dioxide

·         Effective against Giardia and Cryptosporidium protozoa

·         Must be produced on site

·         Takes more technical skill to use

·         Forms bromate and other DBP compounds

·         Requires bromate monitoring 

·         Does not provide residual protection

Ultraviolet Radiation

Non-chemical disinfection by using ultraviolet radiation at certain wavelengths

·         Effective against bacteria, Giardia and Cryptosporidium

·         Does not form DBPs 

·         Disinfection effectiveness and efficiency are affected by turbidity and dissolved substances

·         Less effective against certain viruses

·         Technically complex, requires training to operate equipment

·         Does not provide residual protection (may need secondary disinfectant)

·         Does not reduce DBP formation by secondary disinfectant