[Advances in Chemistry] Aquatic Humic Substances Volume 219 (Influence on Fate and Treatment of Pollutants) || Effect of Ozonation and Chlorination on Humic Substances in Water

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  • 37 Effect of Ozonation and Chlorination on Humic Substances in Water

    Joop C. Kruithof, Marten A. van der Gaag, and Dick van der Kooy

    Kiwa Ltd., P.O. Box 1072, 3430 BB Nieuwegein, Netherlands

    Ozonation converts humic substances, as can be seen by a small decrease in dissolved organic carbon (DOC) and a substantial de-crease in UV extinction. This conversion is related to the formation of low-molecular-weight biodegradable compounds, which enhance regrowth of organic substances in water during distribution. Post-treatment by coagulation and filtration processes can remove these types of compounds. Chlorination of humic substances causes the production of trihalomethanes (THMs), high-molecular-weight or-ganohalides, and mutagenicity. A partial THM-precursor removal by pretreatment does not reduce the THM content under practical conditions and causes a shift to production of more highly brominated THMs. Extensive pretreatment with ozonation and granular activated carbon (GAC) filtration lowers the adsorbable organohalogen (AOX) content and the mutagenic activity in the Ames test.

    WATER SOURCES USED FOR DRINKING-WATER PREPARATION contain humic substances, which account for roughly 75% of the total dissolved organic carbon (DOC). These humic substances strongly interfere with water-treatment processes, especially in surface-water treatment. Therefore, the Netherlands Waterworks Testing and Research Institute Kiwa Ltd. and the Netherlands Waterworks have been carrying out investigations into the removal and conversion of bulk organic materials (mainly humic substances) by water-treatment processes.

    0065-2393/89/0219-0663$06.00/0 1989 American Chemical Society

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    In Aquatic Humic Substances; Suffet, I., et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1988.

  • 664 AQUATIC HUMIC SUBSTANCES

    Many analytical methods are available for a general characterization of humic substances in water: determination of D O C content as a measure of the concentration of humic substances; spectrophotometric analysis (measurement of U V extinction and color) as a measure of the concentration and, in combination with the D O C content, as a first indication of the character of the humic substances; and gel permeation chromatography and X-ray scattering to determine the molecular-size distribution. Other methods are used to assess the interference of humic substances with treatment processes. Examples of these methods are determination of easily assimilable organic carbon (AOC) content as a measure of the regrowth potential of the organic materials, especially after oxidative treatment, and determination of trihalomethane (THM) precursors as a measure of the potential T H M formation upon chlorination.

    A l l of these parameters have been used to characterize the concentration and nature of humic substances during Dutch drinking-water treatment. For this chapter we will concentrate on

    D O C content as a measure of the content of humic substances

    UV254 extinction at a wavelength of 254 nm as an indication of the changing character of the humic substances during oxidative treatment

    A O C content as a measure of the regrowth potential of the water

    THM-precursor content as a measure of potential T H M formation upon chlorination.

    Treatment processes influencing the concentration of humic substances are coagulation and granular activated carbon (GAC) filtration. Standardized jar test equipment was developed (1) to study the effect of coagulation on the content of natural organic compounds. G A C filtration is applied at 12 full-scale plants, primarily to remove toxic compounds and to improve taste (2, 3). Removal of humic substances (removal of color, U V extinction, and dissolved organic carbon) is an important secondary aim.

    This chapter will consider the interaction of oxidative processes with humic substances in water. The processes studied most extensively are ozonation and chlorination.

    Data on oxidation of humic substances by ozonation are available from 12 pilot-scale and eight full-scale experiments (4). Ozonation of humic substances leads to the production of low-molecular-weight compounds, which increase the availability for bacteria of organic compounds in water. This phenomenon is responsible for the regrowth of bacteria during distribution (5). Removal of these biodegradable compounds by posttreatment of the ozonated water is necessary to restrict bacterial regrowth during distribution

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    In Aquatic Humic Substances; Suffet, I., et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1988.

  • 37. KRUITHOF ET AL. Effect of Ozonation and Chlonnation 665

    (6). The effects of ozonation will be illustrated through D O C , U V extinction, and A O C measurements gathered from pilot-scale and full-scale experiments carried out at the treatment plants at Driemond (Municipal Waterworks of Amsterdam) and at Kralingen (Waterworks of Rotterdam).

    In the years since the discovery of T H M production during drinking-water chlorination (7, 8), measures have been taken to reduce this side effect of chlorination as much as possible (9). One option was the removal of humic substances by G A C filtration before chlorination. Under Dutch chlorination conditions, partial removal of humic substances by G A C filtration did not give a substantial reduction of the T H M content for long GAC-filter running times. Moreover, chlorination of GAC-filter effluents caused a shift to the production of more highly brominated T H M s , especially at short GAC-filter running times (10-12).

    In addition to a relatively high adsorbable organic halogen (AOX) content, mutagenic activity was found after postchlorination with a relatively low chlorine dosage of about 0.5 mg/L (13, 14). Both side effects of chlorination will be illustrated on the basis of T H M and THM-precursor measurements gathered from full-scale experiments carried out at the treatment plant at Zevenbergen (Waterworks of North West Brabant) and on the basis of A O X and mutagenic activity measurements carried out at the pilot plant at Nieuwegein (Kiwa Ltd).

    Effects and Side Effects of Ozonation

    Experimental Parameters. An impression of the character and the content of humic substances in the water was obtained by determination of the UV extinction and the DOC content. In samples of nonozonated and ozonated water, the UV extinction was determined by spectrophotometer (Perkin Elmer, Type 500S) at a wavelength of 254 nm. The DOC content was determined subsequently, after acidification to pH 2 with concentrated hydrochloric acid and membrane filtration, with an ultra-low-level organic analyzer system (Dohrmann DC-54).

    To determine the concentration of AOC, 600 mL of water was heated in thoroughly cleaned Pyrex Erlenmeyer flasks at 60 C for 30 min to inactivate the bacteria orginally present in the water. After cooling, pure cultures of selected bacteria were inoculated into the samples, which were incubated at 15 C. Growth of these bacteria in the water samples was measured by periodic determinations of the number of viable organisms. The maximum colony count is considered a measure of the amount of AOC available for the organism in the water used in the growth experiment.

    Two bacterial strains were used: Pseudomonas fluorescens strain P17, able to metabolize a great variety of organic compounds such as amino acids, carbohydrates, and aromatic acids: AOC (P17); and Spirillum species strain NOX, specialized in the use of carboxylic acids such as formic acid, glyoxylic acid, and oxalic acid: AOC (NOX). Yield values of P17 for acetate and of NOX for oxalate have been determined for use in calculation of the AOC concentration. The total AOC (AOCT) is AOC T = AOC (P17) + AOC (NOX). In this equation, AOC (P17) is expressed in micrograms of acetic acid carbon (Ac C) per liter and AOC (NOX) is expressed in micrograms of oxalic acid carbon (Ox C) per liter. Detailed information about the determination has been published elsewhere (6, 15, 16).

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    In Aquatic Humic Substances; Suffet, I., et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1988.

  • AQUATIC HUMIC SUBSTANCES

    Application of Ozonation. In the Netherlands ozone is applied at eight full-scale treatment plants. The two largest plants are the Driemond plant of the Municipal Waterworks of Amsterdam with a production of 22 10 6 kL/year and the Kralingen plant of the Waterworks of Rotterdam with a production of 33 X 10 6 kL/year. The tr

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