Trihalomethanes chlorination

Trihalomethanes. Wherever chlorine is used as a disinfectant in drinking-water treatment, trihalomethanes (THMs) generaUy are present in the finished water. The THMs usuaUy formed are trichloromethane (chloroform), bromodichloromethane, dibromochloromethane, and tribromomethane (bromoform). There are four main techniques for the analysis of THMs headspace, Hquid— Hquid extraction (Ue), adsorption—elution (purge—trap), and direct aqueous injection. The final step in each technique involves separation by gas—Hquid chromatography with a 2 mm ID coUed glass column containing 10 wt % squalene on chromosorb-W-AW (149—177 p.m (80—100 mesh)) with detection generaUy by electron capture. 

Under drinking water plant treatment conditions, humic materials and/ or resorcinol do not produce trihalomethanes with chlorine dioxide even when a slight excess of chlorine (1 percent to 2 percent) is present. Also, saturated aliphatic compounds are not reactive with chlorine dioxide. Alcohols are oxidized to the corresponding acids. 

Methyl ketones 1, as well as acetaldehyde, are cleaved into a carboxylate anion 2 and a trihalomethane 3 (a haloform) by the Haloform reaction The respective halogen can be chlorine, bromine or iodine. 

Activated carbon filters are employed primarily as RW contaminant removal systems for chlorine (by chemisorption) and various organics such as trihalomethanes (THMs), petroleum products, and pesticides (by adsorption). In addition, they act as physical filters and therefore incorporate sufficient freeboard in their designs to permit periodic backwashing. 

An overview of the reactions involving trihalomethanes (haloforms) CHXYZ, where X, Y, and Z are halogen atoms, has been given in the context of ozone depletion (Hayman and Derwent 1997). Interest in the formation of trichloroacetaldehyde formed from trichloroethane and tetrachloroethene is heightened by the phytotoxicity of trichloroacetic acid (Frank et al. 1994), and by its occurrence in rainwater that seems to be a major source of this contaminant (Muller et al. 1996). The situation in Japan seems, however, to underscore the possible significance of other sources including chlorinated wastewater (Hashimoto et al. 1998). Whereas there is no doubt about the occurrence of trichloroacetic acid in rainwater (Stidson et al. 2004), its major source is unresolved since questions remain on the rate of hydrolysis of trichloroacetaldehyde (Jordan et al. 1999). 

Although reactions carried out by ozone have attracted enormous attention in the atmospheric environment, ozone has also been used extensively in the treatment of drinking water without the production of undesirable trihalomethanes from the use of molecular chlorine (Richardson et al. 1999). It has been examined for the removal of a number of contaminants, and ozone is considered to be a selective oxidant, even though quite complex reactions may occur. 

Chlorine dioxide has been used widely in Europe since the early 1940 s as a drinking water disinfectant. More recently the USA has suggested the use of chlorine dioxide to reduce the formation of chloro-organic compounds particularly chloroform and other trihalomethanes (THM s) which are known carcinogens(7). 

Disinfection by-products (e.g., adsorbable organic halides such as trihalomethanes) are more than 50% decreased compared to equivalent chlorine treatments in standardized AOX test with STABREX3. In practice, disinfection by-products are decreased even further in STABREX applications because less oxidant is required to control the microbial fouling process compared to bromine or chlorine applications. 

Please indicate which six of the following issues are the most important when considering the comfort and well-being of users and staff. (Air temperature, bacteria, chloramine levels in the water, chlorinous smells, clear water, fresh air, humidity, pH, residual disinfectant level, trihalomethanes, water temperature, water balance)... 

We mentioned in Chapter 2 (Section 2.6.1) that a purge-and-trap procedure sometimes precedes an analysis by gas chromatography. An example of this procedure is found in the City of Lincoln, Nebraska, Water Treatment Plant Laboratory. Water treatment includes chlorination. When water is chlorinated, chlorine reacts with organic matter to form trihalomethanes (THMs), such as chloroform, bromoform, bromodichloromethane, and chlorod-ibromomethane. THMs in water are regulated by the Safe Drinking Water Act, and so the laboratory must analyze the treated water to determine their concentration. 

The interactions of chloroform with other chemicals are an issue of great importance as with many chemicals, exposure to chloroform alone seldom occurs. This is especially true when considering exposure to chlorinated water, which usually contains other trihalomethanes and may contain other potential toxicants. 

Copaken J. 1990. Trihalomethanes Is swimming pool water hazardous. In Water chlorination Chemistry, Environmental Impact and Health Effects, volume 6. Chelsea, MI Lewis Publishers, Inc. 

Dunnick JK, Melnick RL. 1993. Assessment of the carcinogenic potential of chlorinated water experimental studies of chlorine, chloramine, and trihalomethanes. J Nad Cancer Inst 85(10) 817-822. 

Furlong EAN, Dltri FM. 1986. Trihalomethane levels in chlorinated Michigan drinking water. Ecological Modelling 32 215-225. 

Hollod GJ, Wilde EW. 1982. Trihalomethanes in chlorinated cooling water of nuclear reactors. Bull Environ Contam Toxicol 28 404-408. 

B LLE GC Method (Trihalomethanes and Chlorinated Organic Solvents)... 

Thomas RF, Weisner MJ, Brass HJ (1980) The fifth trihalomethane dichloroiodomethane. Its stability and occurrence in chlorinated drinking water. In Jolley RL, Brungs WA, Gumming RB, Jacobs VA (eds) Water chlorination environmental impact and health effects, vol 3. Ann Arbor Science, Ann Arbor, MI, pp 161-168... 

Uses. One of four common trihalomethanes formed after chlorination of water supplies in the past used to make fire extinguisher fluids. 

There is no clear epidemiological evidence for the carcinogenicity of chlorodibromomethane in humans. However, a number of studies suggest an association between chronic ingestion of trihalomethanes in chlorinated drinking water and increased risk of bladder or colon cancer. These smdies cannot provide information on whether any observed effects are due to chlorodibromomethane or to one or more of the hundreds of other by-products that also are present in chlorinated drinking water. 

Chlorine dioxide is a very reactive compound and will not exist in the environment for long periods of time. In air, sunlight will quickly break apart chlorine dioxide into chlorine gas and oxygen. In water, chlorine dioxide will react quickly to form chlorite ions. In water treatment systems, chlorine dioxide will not form certain harmful compounds (e.g., trihalomethanes) when it reacts with dissolved organic compounds. Chlorine dioxide does form other disinfection byproducts, such as chlorite and chlorate ions. 

Other DBFs (e.g., lower chlorinated organics, chlorate, and chlorite) which may be found in drinking water treated with chlorine dioxide (Aieta and Berg 1986 Chang 1982 Stevens 1982). Suh and Abdel-Rahman (1985) reported that the presence of CIO2 and HOCl (CI2 dissolved in water) inhibit the formation of trihalomethanes, and the degree of inhibition depends on the ratio of CIO2 to HOCl. 

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