Removal of micropollutants during drinking water production from surface water with coagulation - flocculation

摘要

Surface water is an important source for drinking water supply. Organic micropollutants in surface water are present in small concentrations but may have consequences for human health. In this paper, the removal of organic micropollutants from surface water by using traditional technologies (coagulation - flocculation) in drinking water production is studied. Laboratory experiments were carried out to examine to what extent micropollutants are removed during coagulation - flocculation. Experiments were done with river water (Dijle river, Leuven, Belgium). The pH of the samples varied from 7 to 7.6 which is in the range of optimal pH in coagulation - flocculation. Four different micropollutants (aldrin, dieldrin, atrazine and bentazon) were studied with different concentrations and different amounts of coagulant Al_2(SO_4)_3.18H_2O. The removal rate of the studied micropollutants seemed to be dependent on the hydrophobicity of the components. Freundlich isotherms were calculated for the tested micropollutants to calculate the adsorption capacity. When comparing the hydrophobicity of the tested pesticides (expressed with log Kow) with the calculated log K values, it can be seen that the higher the hydrophobicity, the higher the adsorption capacity (see figure 1). There was a decrease in removal efficiency for different pesticides from surface water during coagulation -flocculation: aldrin (log Kow = 6.75, log K= 0.71), dieldrin (log Kow = 5.45, log K = 0.28), atrazin (log Kow = 2.82, log K = -0.14) and bentazon (log Kow = 1.67, log K= -0.57). Coagulation - flocculation can remove some organic fraction in water but the removal efficiency is too low as a stand - alone process in most cases. Therefore, in drinking water production, other techniques have to be added for moderate to high concentration of micropollutants.