Water, potable dechlorination

This chapter only discusses the applications of chlorination and chloramination in potable water treatment. In case the two processes are to be used for wastewater treatment, residual chlorine concentration in the plant effluent may become a regulatory issue (30). Selection of an alternative disinfectant becomes more important. New alternative disinfectants have been studied by Wang (19-25). Wang (35,36) also reported that UV is an effective process for dechlorination, dechloramination, or de-ozonation. 

Chloramine reactions do not release COj gas or destroy the integrity of the carbon. However, chloramine reactions are much slower than chlorine reactions with activated carbon. Finally, although carbon can effectively remove chlorine from potable water, it is more expensive than other dechlorination methods (9,10). 

The limitations to using catalytic carbon for potable water dechlorination include (i) inability to dechlorinate free chlorine (only chloramines are removed by catalytic carbon) and (ii) potential loss of carbon life due to fouling by organic compounds or oxidation by various compounds. Furthermore, catalytic carbons are generally more expensive than activated carbon as well as other dechlorination methods currently available. 

Sodium ascorbate is the sodium salt of ascorbic acid. Most of sodium ascorbate reactions with chlorinated waters are similar to those of ascorbic acid. However, a key difference in dechlorination using sodium ascorbate is that it does not lower the water pH. Several utilities in the Pacific Northwest have evaluated the use of sodium ascorbate for neuhalizing chlorine from potable water releases. The pH of sodium ascorbate is approximately neuhal. The expected reaction of sodium ascorbate with chlorine is shown below ... 

Fig. 1. Chlorine concentrations at Tacoma City Water when stoichiometric concentrations of dechlorination chemicals were added to neutralize chlorine in potable water from a hydrant. The water traveled a distance of about 450 ft after 250 s.

Contents indude chlorine manufacture, properties, hazards and uses, hypochlorination. onsite generation, chlorine residuals, potable water and wastewater chlorination, facility design, dechlorination, operation and maintenance, chlorine dioxide, ozone, peroxone andAOxPs, bromine, iodine, and ultraviolet... 

Sources include surface waters, wells, seas and estuaries, and recovered condensate. Many plants serve all their needs with municipal water, treated to potable quality, which may be based on surface water or well water. Public water supplies usually carry a firaction of a ppm of chlorine. When used as the principal supply to a plant, these must be dechlorinated before most direct uses in the process. 

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