Jar Tests for Evaluation of Atrazine Removal at Drinking Water Treatment Plants

Abstract

The objective of this study was to evaluate the effects of major factors such as PAC dosage, pH, contact time, mixing energy, alum dosage, and enhanced coagulation on the effectiveness of atrazine removal. Jar tests and response surface methodology were used to simulate conditions found in different treatment facilities. The time course of atrazine concentration with an initial atrazine concentration of 12 μg/L and initial (Acticarb) PAC of 16 mg/L indicated that it took approximately 5 days to reach equilibrium with the maximum atrazine removal of about 73%. Therefore, in treatment facilities, the adsorption of atrazine with this kind of PAC will be less than the removal achieved at equilibrium, due to the short retention time in a dynamic process. Mixing energy is a major factor affecting atrazine absorption. With jar test times ranging from 30 to 60 min, increasing rpms from 5 to 100 (G = 4 to 321 s−1) resulted in atrazine removals ranging from 34 to 59%. Without addition of PAC, neither lime softening nor alum coagulation (conventional or enhanced dosages ranging from 6 to 18 mg/L) demonstrated atrazine removal. A synergistic relationship appears to exist between PAC dosage and enhanced coagulation (with pH adjusted to about 5.8); neither PAC nor enhanced coagulation resulted in as high a removal rate of atrazine as the two did together (greater than 60%). The results of this study are useful for evaluation of different PAC application points in conventional drinking water treatment plants. Key words: Atrazine; powdered activated carbon (PAC); jar tests