AWWA JAW49904

The effect of granular activated carbon (GAC) service time on the remaining life of GAC adsorbers that are exposed to periodic pollutant episodes was evaluated. Equilibrium and kinetic parameters describing the adsorption of atrazine were determined for GAC that had been preloaded with backgound organic matter (BOM) for as long as 25 months. Furthermore, atrazine removal was measured in pilot tests employing GAC that had been preloaded for five and 20 months. Isotherm data showed that: preloaded BOM sharply reduced the remaining adsorption capacity of GAC for atrazine; competitive adsorption was not important on the tested prelaoded GAC samples; and, use of pulverized preloaded GAC led to an overestimate of remaining adsorption capacity. Preloading had the greatest effect on GAC capacity; adsorption kinetics were not affected as severely. The homogeneous surface diffusion model was used to predict atrazine removal in pilot tests and to predict remaining GAC life. For the given adsorbent and background water, remaining life predictions for atrazine removal are presented for scenarios that may be typical for utilities in the midwestern United States and in western Europe. Includes 43 references, tables, figures.