Bleaching of color of kraft pulp mill effluents and natural organic matter in lakes

In situ changes in the color of lake water and biologically treated kraft pulp mill effluents mixed in lake water were examined in three lakes. In 1.7 m3 enclosures, the color (400–700 g Pt·m–3) of the mixture of pulp mill effluent and lake water remained similar for 4 months in darkness, whereas exposure to solar radiation resulted in 17–42% bleaching of color. During the summer stratification of a humic lake, the color (160 g Pt·m–3) of hypolimnetic water remained similar to that found during spring turnover, but the color of epilimnion decreased 13%. The measured rates of photochemical bleaching of color by solar radiation could explain the decrease of epilimnetic color. Attenuation of …