Chlorine in water treatment

These halogenated organic substances (e.g., chloroform and carbon tetrachloride) are generated as disinfection byproducts from the use of chlorine in water treatment. 

Measures to prevent transmission include proper disposal of feces, wastewater treatment, and a filtration step before chlorination in water treatment plants that draw from surface water sources. Cooking kills the cysts in contaminated foods and boiling will make water safe for use. For backpackers who walk through the wilderness, iodine has been shown to be a better disinfectant for giardia cyst than chlorine. It should be emphasized that of all the methods of preventing contamination from the cyst, a properly designed and operated water filtration plant is the best line of defense in drinking water supplies. 

Ozone can be used to replace chlorine for the sterilization of water. Replacement of chlorine is desirable because chlorination increases the salinity of water. The more salt in the water the less value it has for later use in, for example, irrigation of cropland. When used to sterilize water, chlorine reacts with trace organic compounds to form carcinogenic chlorine compounds such as chloroform. The use of ozone to replace chlorine in water treatment will eliminate chlorination-induced salinity and carcinogenic chlorinated organic compounds. Because of its instability, any residual ozone not consumed in purifying the water rapidly decomposes to ordinary oxygen. 

Hypochlorous acid reacts very rapidly and quantitatively with a slight excess of free ammonia forming monochloramine, NH2CI, which reacts at a slower rate with additional HOCl forming dichloramine, NHCI2. Trichloramine is formed when three moles of HOCl are added per mole of ammonia between pH 3—4 (100). Hypochlorous acid in the form of chlorine or hypochlorite is used in water treatments to oxidize ammonia by the process of break-point chlorination, which is based on formation of unstable dichloramine. The instabiHty of NHCI2 is caused by presence of HOCl and NCl (101,102). The reaction is most rapid at a pH of about 7.5 (103). Other nitrogen compounds such as urea, creatinine, and amino acids are also oxidized by hypochlorous acid, but at slower rates. Unstable iV-chloro compounds are intermediates in deammination of amino acids (104,105). 

The conditions for chlorate formation are high pH, low reactant concentrations, and the presence of excess chlorine or hypochlorous acid. Thus, the addition of free chlorine or hypochlorite to chlorine dioxide treated water, which contains chlorite as a by-product of the chlorine dioxide treatment, predominandy forms chlorate in the pH 5—8 range typically used in water treatment (140). 

Seek alternatives to chlorine for water treatment and disinfecting applications. For example, sodium hypochlorite has been used both in industrial and municipal water treatment applications (Somerville, 1990). Other alternatives include calcium hypochlorite, ozone, ultraviolet radiation and heat treatment (Negron, 1994 Mizerek, 1996). 

Chlorine is used in a number of industrial processes, including the manufacture of plastics, solvents, and pesticides. It is used as a bleach in the paper and textile industries and as a disinfectant in water treatment (Section 15.6). 

These data show that bromine works better than chlorine in high pH waters such as the ocean. Similarly, most industrial water is quite alkaline and therefore, a practical form of bromine is also preferred. The technical attributes of bromine antimicrobials are of value in water treatment and are apparently also worth the cost to many aquatic plants. Further observations of natural microbial fouling control systems reveal that animals also preferentially manufacture, in situ, certain bromine-based antimicrobials. 

Pure Ti02 was recently reported to be active in the disinfection of water contaminated by spores of the type Fusarium solani [142], Bacillus anthracis [143], or Cryptosporidium parvum oocysts [144], or when supported as nanocomposites on zeolite H(i for E. coli deactivation [145], and it found applications in water treatment as a replacement for chlorine. Ag-Ti02 immobilized systems were used for inactivation of bacteria, coupling the visible light response of the system and the strong bactericidal effect of Ag [146]. Silver was deposited on hydroxyapatite to form nanocomposites with a high capacity for bacterial adsorption and inactivation [147], or used for airborne bacterial remediation in indoor air [148],... 

While hypochlorite in pure solutions is an industrially and commercially useful product, notably in water treatment and disinfection, incidental production exceeds demand. If discharged as a waste stream it can act as a powerful bio-toxin owing to its high oxidation potential, can form chlorinated organics when mixed with other streams and can release chlorine if the stream becomes acidic. There is thus a need to treat these waste hypochlorite streams. 

Another approach consists of an in-situ acetylation and extraction of NPEOs and further analysis of the acetyl derivatives. The method has been applied to analyse effluent water and sewage sludges [102,103], sediments [104] and river waters [105]. Silylated derivatives [106] using BSA or BSTFA have also been used to determine NPEO (n < 6) in seawater [107] and wastewater [107,108], sediments [109] and sludges from wool scour effluents [110]. Halogenated derivatives of alkylphenols (AP) can also be formed as a result of chlorination practices in water treatment or wastewater if bromide is present. Brominated OPs and NPs (BrAPEOs) have been identified by GC-MS in sewage [111] and tap water [89], respectively. 

Chemical/Physical. Chlorination of 2-chloroethyl vinyl ether to a-chloroethyl ethyl ether or P-chloroethyl ethyl ether may occur in water treatment facilities. The alpha compound is very unstable in water and decomposes almost as fast as it is formed (Summers, 1955). Although stable in NaOH solutions, in dilute acid solutions hydrolysis yields acetaldehyde and chlorohydrin (Windholz et al., 1983). At pH 7 and 25 °C, the hydrolysis half-life is 175 d (Jones and Wood, 1964). 

Uses. Chlorinating agent disinfectant laundry bleach in water treatment intermediate for drugs insecticides polymerization catalyst... 

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. 

Dreux M, Lafosse M, Gilbert M, et al. 1985. Analytical determination of inorganic chlorination products in water treatment by an HPLC method. In Jolley RL, Bull RJ, Davis WP, et al., eds. Water chlorination-Chemistry, environmental impact and health effects. Vol. 5. Williamsburg, VA Lewis Publishers, Inc. 

Chlorine dioxide is used for bleaching textdes, paper-pulp, ceUulose, leather, beeswax, ods, and fats. Other applications are in water treatment processes to kill bacteria, oxidize impurities, and control the taste and odor of water. It also is used to prepare many chlorite alts. Dilute solutions are used as antiseptics. 

Chlorine (from the Greek chloros for yellow-green ) is the most abundant halogen (0.19 w% of the earth s crust) and plays a key role in chemical processes. The chlor-alkali industry has been in operation since the 1890s and improvements in the technology are still important and noticeable, for example, the transition from the mercury-based technology to membrane cells [60]. Most chlorine produced today is used for the manufacture of polyvinyl chloride, chloroprene, chlorinated hydrocarbons, propylene oxide, in the pulp and paper industry, in water treatment, and in disinfection processes [61]. A summary of typical redox states of chlorine, standard potentials for acidic aqueous media, and applications is given in Scheme 2. 

In some instances the raw water reaching water treatment plants may contain pathogens such as the human infectious protozoon Cryptosporidium parvum. The environmental form of C parvum is a spheroidal oocyst of 4-6 microns diameter. The oocyst is resistant to conventional chemical disinfectants that are commonly used in water treatment such as chlorine or chloramines. It is therefore essential that Cryptosporidium be removed during the coagulation and filtration processes stage in the water... 

Two-thirds of the chlorine produced in North America is consumed by the organic chemicals industry (25% goes to ethylene dichloride production alone). Pulp and paper mills account for another 15%, while 5% of the total is used in water treatment. All of these applications, however, have environmental implications that led to demands from activist groups that the production of chlorine derivatives be reduced (even, in the extreme view, phased out entirely). While these concerns are being taken seriously in all quarters, and some chlorinated products have already been banned, the fact is that chlorine-based technologies make, and will continue to make, important positive contributions to human health and prosperity. Indeed, at the time of writing in 1996, chlorine consumption continues to rise, al-... 

Impurities in water treatment chemicals halogenated hydrocarbons in chlorine, oxides of nitrogen from ozonators, chlorates and chlorites from chlorine dioxide, acrylamide monomers. 

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