Chlorine, for water

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 an efficient disinfectant as well as an oxidizing agent, and perhaps is the most frequently used chemical by environmental engineers and scientists since 1800s. The oldest water treatment facilities used only chlorine for water disinfection, which became the foundation of our industrial development. Today chlorine has been used in various forms for sanitary, commercial, industrial, and military applications. This chapter is a sister chapter to the following book chapters in the Handbook of Environmental Engineering series ... 

As happens in the electrolysis of other salts, the chlorine gas that is produced is an important source of chlorine for water purification systems. 

Characterize the common substituents of chlorine for water disinfection and discuss the application of these disinfectants in your country. 

The production of glyphosate herbicide (Round-up), the world s most successful herbicide, is another example of utilization of the catalytic properties of carbon surfaces [338], The Monsanto process by which Round-up is produced uses activated carbon as an oxidation catalyst for one of the key synthesis steps. The catalyst is produced by the treatment of activated carbon with ammonia at a high temperature to impart the desired nitrogen functionality. These functionalities are also commercially important for the reduction of chloramine in potable (drinking) water. Since water utilities are increasingly using chloramine rather than chlorine for water disinfection, and standard activated carbon products are not effective for removal of residual chloramine (which, for example, is highly toxic to dialysis patients), a catalytic carbon must be used to reduce its content [339,340],... 

Hypochlorous acid, formed when chlorine dissolves in water, is antimicrobial. This is the basis for the use of chlorine and halazone in water purification. Organic matter binds chlorine, thus preventing antimicrobial actions. In a given water sample, this process is referred to as the chlorine demand, since the chlorine-binding capacity of the organic material must be exceeded before bacterial killing is accomplished. Many preparations of chlorine for water purification do not eradicate all bacteria or entamoeba cysts. 

For workplaces placed close to the coinmunity or involving non-employees (such as shoppers) in a workplace, this approach includes appropriate measures to protect them. A safety case has been nm, for example, for a public swimming pool using cylinders of chlorine for water treatment. A safety case nm on the Bhopal pesticide plant in India would have identified the problem of a lack of buffer zone due to poor, if not non-existent, enforcement of local govermnent residential area planning. As it was, in 1986 too mat r residents were living too close to the plant. 

There are in fact some bromine applications that are not questioned from an environmental point of view. Bromine has a similar usage to chlorine for water disinfection. Silver bromide is used as a Hght-sensitive substance in photographic emulsions. A quarter of aU bromine used finds its way down into boreholes in oilfields, where calcium and zinc bromide solutions are used as drilling fluids. In high concentrations, the liquids are heavy and exert a high hydrostatic pressure that prevents the very disturbing blow-out situations. 

Another consideration of growing importance in water treatment is the development of new technologies. These include special membrane processes for water filtration, alternatives to chlorine for water disinfection, advanced oxidation of impurities, and the use of ultraviolet radiation for water disinfection and as an aid to destruction of organic contaminants by oxidants. It is important to consider the sustainability of developing techniques including costs and by-product generation. 

Concentrated sulphuric acid has a strong affinity for water and great heat is evolved on mixing hence the acid must be added to water to dilute it. Because of this affinity, the acid can be used to dry gases with which it does not react, for example oxygen, chlorine, sulphur dioxide, and is used in desiccators. It will remove water of crystallisation from some compounds, for example... 

Phosphoms trichloride reacts readily with oxygen, sulfur, chlorine, and water. It serves as an intermediate in the production of phosphoms oxychloride, phosphoms sulfochloride, phosphoms pentachloride, and phosphonic (phosphorous) acids. PCl is also the raw material for the manufacture of dialkyl phosphonates,... 

Chlorine. Chlorine is a weU known disinfectant for water and wastewater treatment, however, it can react with organics to form toxic chlorinated compounds such as the tribalomethanes bromodichloromethane, dibromochloromethane, chloroform [67-66-3] and bromoform [75-25-2]. Chlorine dioxide [10049-04-4] may be used instead since it does not produce the troublesome chlorinated by-products as does chlorine. In addition, by-products formed by chlorine dioxide oxidation tend to be more readHy biodegradable than those of chlorine, however, chlorine dioxide is not suitable for waste streams containing cyanide. 

Zirconium tetrachloride is instantly hydrolyzed in water to zirconium oxide dichloride octahydrate [13520-92-8]. Zirconium tetrachloride exchanges chlorine for 0x0 bonds in the reaction with hydroxylic ligands, forming alkoxides from alcohols (see Alkoxides, METAl). Zirconium tetrachloride combines with many Lewis bases such as dimethyl sulfoxide, phosphoms oxychloride and amines including ammonia, ethers, and ketones. The zirconium organometalLic compounds ate all derived from zirconium tetrachloride. 

The largest use of calcium hypochlorite is for water treatment. It is also used for I I and household disinfectants, cleaners, and mildewcides. Most of the household uses have been limited to in-tank toilet bowl cleaners. In areas where chlorine cannot be shipped or is otherwise unavailable, calcium hypochlorite is used to bleach textiles in commercial laundries and textile mills. It is usually first converted to sodium hypochlorite by mixing it with an aqueous solution of sodium carbonate and removing the precipitated calcium carbonate. Or, it can be dissolved in the presence of sufficient sodium tripolyphosphate to prevent the precipitation of calcium salts. However, calcium hypochlorite is not usually used to bleach laundry and textiles because of problems with insoluble inorganic calcium salts and precipitation of soaps and anionic detergents as their calcium salts. 

Today most salt is used to make caustic soda and chlorine (see Alkali and chlorine products, chlorine and sodiumhydroxide). These chemicals are used in thousands of household products. The next biggest use is for highway deicing. Other uses are for water softening, Hvestock feeds, meat packing, and foodstuffs. 

An integrated process for producing chlorine dioxide that can consume chlorine (46) involves the use of hydrochloric acid as the reductant. The spent chlorine dioxide generator Hquor is used as feed for chlorate production, and hydrogen gas from chlorate production is burned with chlorine to produce hydrochloric acid. The principal disadvantage in the integrated hydrochloric acid-based processes is that the chlorine dioxide gas contains Y2 mole of chlorine for each mole of chlorine dioxide produced. A partial purification is achieved by absorption in chilled water in which the solubiHty of chlorine is less than chlorine dioxide however, this product stiU contains 10—15% chlorine on the basis of total chlorine and chlorine dioxide. 

Chlorine dioxide yields of 95% or greater have been demonstrated. The use of chlorine as an oxidant has distinct advantages because it is usually present in municipal water treatment plants for water disinfection. 

The energy requirements for desorbing 1,1-dichloroethane from activated carbon in a stripping—adsorption process for water purification have been calculated at 112 kj/kg (14). Chlorinated hydrocarbons such as 1,1-dichloroethane may easily be removed from water by air or steam stripping. 

The reaction of aHyl chloride and chlorine ia water produces trichloropropane as a by-product even ia the aqueous phase, along with tetrachloropropyl ether. For maximum dichi orohydrin yield it is necessary to mn the reaction at low concentrations of chloride ion and of chlorohydrin, that is, with high water dilution. However, high dilution results ia an aqueous effluent that contains minor amounts of these by-products that require significant treatment to reduce them to levels acceptable ia outfalls to rivers, lakes, and other pubHc waterways. 

The dissociation of hypochlorous acid depends on the pH. The unionized acid is present in greater quantities in acid solution, although in strongly acid solution the reaction with water is reversed and chlorine is Hberated. In alkaline solutions the hypochlorite ion OCL is increasingly Hberated as the pH is increased. The pH is important because unionized hypochlorous acid is largely responsible for the antimicrobial action of chlorine in water. Chlorine compounds are therefore more active in the acid or neutral range. The hypochlorites most commonly employed are sodium hypochlorite [7681-52-9] or calcium hypochlorite [7778-54-3]. 

Environment Internal Cooling water near ambient temperature, intermittent low flow, daily chlorination for 1 hour... 

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