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The objectives of this investigation were to study various physical and chemical properties of organic color in water, and to determine the degree of uniformity with which these properties occur in colored waters by analyzing samples from a variety of sources. The color in these waters is due to light scattering and fluorescence rather than molecular absorption of light energy. The pH value of the waters was found to affect both the particle size and number of particles in a given suspension. This effect was proposed as an explanation for the variation of color value with pH. The fluorescence spectra of these colored waters were recorded and revealed in all waters a maximum energy of emission at 490 Mμ, with the combined excitation wavelengths of 365,404, and 436 Mμ. The particle size of the organic matter in each water was estimated at constant pH by dialysis and membrane filtration and was found to be generally less than 10 Mμ. The coagulation behaviors of these waters with aluminum sulfate were compared, and it was observed that the pH zone of optimum color removal was accompanied by a zone of minimum zeta potential and, typically, of charge reversal, of the coagulated color particles.
Black et al. (1963) studied this question.