The Effect of Ozonation on the Removal of Organics by Coagulation – Flocculation

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Abstract
We present here some works which take place in the particular framework of the study of drinking water treatment of reservoir waters which contain high concentrations of organics, mainly humic substances. Previous studies on coagulation of fulvic acid solutions have proved that the optimal removal of organic matter was reached at acidic pH with 2 mg of ferricion per mg or organic carbon (summarized in this paper). The main question in this study is to know what is the impact of preozonation on the removal of organics by iron (III) coagulation. The study of the behavior of organics, in terms of UV-absorbance and TOC measurements was made on three aquatic fulvic acids and on two raw waters. The experiments carried out with fulvic acids showed that preozonation (at 0.5 mg O3/mg C) of fulvic acid appeared to have shifted the region of the optimal DOC removal towards the higher coagulant dose. Furthermore, increasing ozone doses led to a slight decreasing of coagulation efficiency at constant coagulant dose. With two raw waters, preozonation at low ozone doses (0.2 mg 03/mg C) was found to improve very slightly the elimination of organic matter, while high ozone doses (0.9 mg O3/mg C) led to a disturbance of TOC elimination by iron coagulation.