Degradation kinetics of atrazine and its degradation products with ozone and OH radicals: A predictive tool for drinking water treatment

The present study investigates the degradation of atrazine (2-chloro-4-(eth ylamino)-6-isopropylamino-s-triazine) by ozone and OH radicals during ozona tion and advanced oxidation processes, with the identification of the main degradation products. Besides the dealkylated and amide degradation product s(6-amino-2-chloro-4-isopropylamino-s-triazine, 6-amino-2-chloro-4-(ethylam ino)-s-triazine, 4-acetamido-2-chloro-6-isopropylamino-s-triazine, 4-acetam ido-6-amino-2-chloro-s-triazine, and chlorodiamino-striazine), two new degr adation products with an imine group were identified (2-chloro-4-ethylimino -6-isopropylamino-s-triazine and 6-amino-2-chloro-4-ethylimino-s-triazine). The contribution of the different pathways (direct ozone and OH radical re action) to the overall degradation process has been quantified, and the rat e constants of the reactions of atrazine and its main degradation products with both oxidants have been measured. The ethyl group is more reactive tha n the isopropyl group (i.e. 19 times during ozonation and four times during OH radical attack). The ethyl group reacts in higher proportion through ox idation to acetamide or imine derivates than to dealkylation. In contrast, the isopropyl group reacts mainly through dealkylation to the free amino gr oup. Acetamido and imino groups a re found to be resistant to chemical oxid ation. These reactivities were corroborated by the measured values of the r ate constants with both oxidants. A combination of product distribution and the kinetic parameters together with ozone and OH radical concentrations a llowed us to calculate the evolution of the concentration of the degradatio n products for a given ozonation process.