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To what extent are pesticides removed from surface water during coagulation–flocculation?

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Abstract

The occurrence of pesticides in drinking water sources is of concern for drinking water production companies as well as for the end users. However, it is still unclear which pesticides are removed, and to what extent, in widely used treatment methods such as coagulation–flocculation. Pesticides possibly interact with colloidal particles by adsorption on the flocs during coagulation–flocculation. In this study, removal of four pesticides (aldrin, dieldrin, atrazine, bentazon) was observed during jar test experiments in distilled and surface water (Dijle river, Belgium), using aluminium sulphate as a coagulant in different amounts ranging from no coagulant to high doses (300 mg/L). Without aiming at an accurate description of the removal process, the purpose of this study was to evaluate how much of the pesticides can be removed by changing the concentration, the dosage, the water matrix and the properties of the pesticides. The results show that the removal is usually low. The efficiency was worse when the matrix was distilled water than for Dijle river water, which is consistent with the idea that the removal of micropollutants only occurs through adsorption on the available organic material, and not on inorganic coagulants. Sorption on the natural material available in the Dijle river water seemed to be the main mechanism controlling the removal of micropollutants with coagulation/flocculation, rather than the amount of coagulant added. The hydrophobicity of the compounds was found to be a major factor in determining the removal efficiency with coagulation–flocculation; the most hydrophobic compound had the highest removal efficiency. Nevertheless, the removal was below 50% under all the tested circumstances. The results of this study prove that pesticide removal in conventional water treatment plants depends on physico-chemical interactions, but is insufficient even with extreme doses of alum.
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Keywords: coagulation–flocculation; drinking water production; hydrophobic pesticides; pesticides

Document Type: Research Article

Affiliations: 1: Laboratory for Applied Physical Chemistry and Environmental Technology, Department of Chemical Engineering, Leuven, Belgium; 2: Department of Sanitary Engineering, Faculty of Civil Engineering and Geosciences, Delft University of Technology, Delft, The Netherlands; and 3: Department of Environmental Engineering, Division of Water Supply and Sanitation, Hanoi University of Civil Engineering, Hanoi, Vietnam

Publication date: 2008-09-01

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