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Organic Halide Formation and the use of Pre-ozonation and Alum Coagulation to Control Organic Halide Precursors

University of North Carolina at Chapel Hill, 9/1/80-6/5/84

Investigators: Reckhow & Singer

The objectives of this research were to investigate the formation of organic halides byproducts of chlorination as well as the control of organic halide precursors with ozonation, alum coagulation and the two in combination. Most of the experiments in this work were conducted on solutions of fulvic acid extracted from Black Lake, N. C. The formation of organic halides was explored as a function of chlorine contact time, pH, chlorine dose, and source and type of aquatic humic substance.

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Additional Background: Whenever natural waters or humic substances are chlorinated, significant concentrations of trihalomethanes and total organic halides (TOX) are produced. Health concerns over chlorination by-products have centered on the trihalomethanes and the non-volatile fraction of the TOX. Recent investigations have shown that a major fraction of the non-volatile TOX can be accounted for by trichloroacetic acid and dichloroacetic acid. Dichloroacetonitrile and l,l,l-trichloroacetone are two additional chlorination by-products which have been found to be mutagenic.
This research investigated the formation of these organic halides as well as the control of organic halide precursors with ozonation, alum coagulation and the two in combination. Most of the experiments in this work were conducted on solutions of fulvic acid extracted from Black Lake, N. C. The formation of organic halides was explored as a function of chlorine contact time, pH, chlorine dose, and source and type of aquatic humic substance. It was found that aquatic huinic substances from different sources behaved in a similar fashion with respect to their organic halide formation. Humic acids gave higher organic halide yields than their corresponding fulvic acids. Raw waters showed average organic halide yields similar to the average yields observed for huinic substances on an equivalent carbon basis. The effect of ozonation on organic halide precursor removal was examined as a function of ozone dose, bicarbonate concentration and pH of chlorination. Ozone was effective at removing most organic halide precursors, although some precursor enhancement was seen at low bicarbonate concentrations and a high pH of chlorination. The addition of small amounts of bicarbonate significantly improved the removal of organic halide precursors. The coagulation of organic halide precursors was investigated with and without ozone pretreatment. Alum was found to remove all organic halide precursors within the same alum dose-pH region (optimum pH = 5.0-5.5). Preozonation shifted this removal region up into the high alum dose range. As a result pre-ozonation led to an overall deterioration in the removal of organic halide precursors following coagulation.

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