Mt street res


The Chemical Decomposition of Halogenated Organic Compounds in Drinking Water

UMass Graduate Reseach Council, 1/1/86-12/31/86

PI: Reckhow
Students: Michael Wacks

The objectives of this research were: (1) to determine the degree to which the various hazardous organic by-products of drinking water chlorination (i.e., TOX, halogenated alkyl nitriles, halogenated methyl ketones, and many others) undergo base catalyzed hydrolysis and dehalogenation; and (2) to quantify the rate of this decomposition as a function of both the pH and the concentration of a "model" base/nucleophile.


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Additional Background: It has now been many years since Dutch and American researchers first linked the presence of chloroform and other trihalomethanes (THM's) in finished drinking waters to the practice of chlorination. These early studies along with subsequent work firmly established that the reactions between free residual chlorine and the ubiquitous products of vegetal decay, natural aquatic humic material, are largely responsible for the presence of THM's in treated drinking water.
Since chloroform is a known carcinogen and the other principal THM's are mutagens, the nearly universal presence of these chloroorganics in US drinking waters caused great concern. This concern quickly manifested itself as a federal standard or maximum contaminant level for trihalomethanes in US drinking waters . More recent work, however, has indicated that the THM's may only be the "tip of the iceberg". Other halogenated organic by-products of chlorination (often quantified as the difference between the Total Organic Halide concentration or TOX and the THM concentration) far exceed the quantity of THM's commonly found in finished drinking waters. These "non-THM's" have attracted less attention largely because they are less easily detected and quantified by modern analytical methods. Nevertheless, a recent report indicates that they represent the major portion of the mutagenic activity observed in drinking water extracts and chlorinated humic materials. Efforts at controlling the concentrations of the THM's and TOX in drinking water treatment have met with limited success. One approach has been to remove the compounds once they are formed. This has, in general, proved to
be too costly or not technologically feasible (see Ref 13 for a review of THM control technologies). The other, and more widely adopted approach is to limit the formation of the TOX compounds. This may be accomplished by either replacing chlorine with an alternative oxidant/disinfectant or by reducing the concentration of the humic "precursor" molecules before chlorinating. The conventional treatment processes of coagulation, filtration, and softening all remove humic materials to varying degrees, but often this is not enough.




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