Disinfection By-products In Water

Disinfection By-products In Water

As indicated in previous post, organic and inorganic matter in source water will react with residual disinfecting agents to produce undesirable by-products. Chlorine reacts with heavy molecular NOM and bromide producing THMS and HAA5. THMs consist of chloroform, bromodichloromethane, dibromomonochloromethane, and bromoform. These compounds are all carcinogens. The average concentration limit for total trihalomethanes is 0.080 mg/L (U.S. EPA, 2006). The HAA5 compounds include monochloroacetic acid, dichloroacetic acid, trichloroacetic acid, monobromoacetic acid, and dibromoacetic acid. The average concentration limit for HAA5 is 0.060 mg/L (US EPA, 2006).

Bromate is produced by the reaction of bromide and ozone when ozone is employed as a primary disinfecting agent. The average concentration limit for Bromate is 0.010 mg/L (U.S. EPA, 2006).

Chlorite is produced by the reaction of chlorine dioxide with NOM and inorganic matter. The average concentration limit for chlorite is 1.0 mg/L (U.S. EPA, 2006).

Toxicology studies with laboratory animals shows that disinfection by-products such as chloroform, bromoform, brmodichloromethane, dichloroacetic acid, and bromate are carcinogens. Chlorite, bromodichloromethane, and certain haloacetic acids cause adverse reproductive and/or development effects in laboratory animals (U.S. EPA, 1998).

Chloroform is the predominant THM compound. If we use activated carbon then it has limited ability to remove chloroform. The presence of chloroform in final product water from a USP Purified Water system is common when THMs are present in feed water.

For USP Water for Injection systems, chloroform, a volatile organic compound, may be present in distilled product water. Again, the concentration of chloroform in USP Water for Injection systems with raw feed water from a surface source should also be determined periodically.

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