Effect of natural organic matter loading on the atrazine adsorption capacity of an aging powdered activated carbon slurry

The effect of natural organic matter loading and calcium carbonate precipitate towards atrazine adsorption capacity of an aging powdered activated carbon slurry was investigated in an hybrid membrane process consisting of an immersed microfiltration membrane system in a completely stirred tank reactor containing powdered activated carbon. The reactor was fed with clarified Seine river water containing natural organic matter (NOM). Samples of the slurry were taken from the reactor and dried at low temperature to avoid the adsorbed NOM degradation. Thermal and CaCO3 analyses were carried out to characterize each sample. The adsorption capacity of each sample was measured by the classical method of isotherms, a modelling method was applied to predict the adsorption capacity in natural water. Kinetic experiments were carried out and the results were also modelized to determine kinetic parameters (k(f) and D-s), The isotherms showed a significant decrease of the capacity during the 62 d of aging (from 3.4 to 0.4 mg g(-1) for an equilibrium concentration of 0.1 mu g L-1 in distilled-deionized water). A linear relationship was found between the Freundlich constant K and the age (r(2) > 0.9). The kinetic experiments showed also the decrease of the D-s value m(from 1.16 x 10(-15) to 8.3 x 10(-17) m(2) s(-1)) while k(f) remained constant and appeared as a non-limiting parameter. Operating charts based on these results were drawn as tools for operators giving operating conditions (age of PAC slurry and fresh PAC dosage rate) to remove a given concentration of atrazine. (C) 1999 Elsevier Science Ltd. All rights reserved.