Impact of natural organic matter compounds on pesticide adsorption on activated carbon

Activated carbon is used in drinking water treatment in order to deliver water according to the European standards on pesticides concentrations (Directive 98/83/EC- O.J. 05/12/98). However, the impacts of dissolved natural organic matter (N.O.M.) compounds reduce strongly pesticides adsorption on powder and granular activated carbon. This paper describes a study on the influence of the main dissolved natural organic compounds from river, fulvic acids (F.A.) and humic acids (H.A.), on atrazine and MCPA adsorption on powder activated carbon (F-400, Chemviron Carbon). The aim of this study is to determine the adsorption behaviour of two pesticides specifically according to the F.A. and H.A. concentrations. The methods used consist of adsorption kinetics and adsorption isotherms. These were carried out: in mineral reconstituted water, based on Meuse river composition, in mineral and organic reconstitued waters (with different F.A. and H.A. concentrations) and in Meuse river water. The results are analysed with the Freundlich equation. Allowing for this pattern, it is possible to determine the impacts of F.A. and H.A.concentrations on the adsorption decreasing of these two pesticides. The results demonstrate that the influence of F.A. and H.A. leads to a decrease of adsorption capacity according to an exponential decreasing pattern. The impacts on MCPA and atrazine adsorption perform a same profile but appear quantitatively different. first because of their different adsorption coefficients (KF) in mineral reconstitued water (atrazine is adsorbed about 3 times higher than MCPA) and secondly according to the F.A and H.A concentrations. In our experimental conditions, the comparison of F.A. and H.A, impacts on adsorption decreasing shows clearly that a same Kf result is achieved with a 4 times lower H.A. concentration than F.A for both pesticides. Taking into account the results in Meuse river and those in reconstituted waters, it appears that the influences of F.A. and H.A. are not additional. In conclusion, according to their concentrations, the F.A. and H.A. of the dissolved .N.O.M. are responsible for a large part of the adsorption competition effect against MCPA and atrazine. According to their own characteristics, the impact of H.A. in comparison with F.A., reduces more the adsorption capacity for both pesticides.