Effect of preadsorbed background organic matter on granular activated carbon adsorption of atrazine

This study examines the effect of preadsorbed background organic matter (measured as dissolved organic carbon, DOC) on the granular activated carbon (GAC) adsorption of atrazine. Thirty-four experiments were conducted in batch contactors using organic-free laboratory water (< 0.1 mg/l DOC) and pilot-column GAC, preloaded with DOC for 3-20 weeks (equivalent to 4.3-32 mg DOC/g GAC). Freundlich isotherms were determined for adsorption of atrazine at initial concentrations from 10 to 1000 micrograms/l. The isotherm data indicate that GAC capacities for atrazine are only moderately reduced by preadsorbed DOC. At an initial concentration of 1000 micrograms/l atrazine, the GAC capacity for atrazine decreases by -1.0 mg atz/mg preadsorbed DOC. At an initial concentration of 10 micrograms/l atrazine, the GAC capacity for atrazine decreases by only -0.40 mg atz/mg preadsorbed DOC. For the pilot-column GAC preloaded with a maximum of 32 mg DOC/g GAC, the decrease in capacity for atrazine averages -33 +/- 13%.