Atrazine (2-chloro-4-ethylamino-6-isopropylamino-1,3,5-triazine) (ATZ) is one of the components of S-triazine. Due to its certain characteristics, ATZ causes pollution in various ecosystems and has been of concern for its probable carcinogenic effects on humans. Researchers have used chemical and physical methods for removing ATZ from the environment. Although these methods are quick, they have not been capable of complete mineralization. Therefore, researchers are looking for methods with lower energy consumption and cost and higher efficiency. In this study, biodegradation of ATZ by microbial consortium was evaluated in the aquatic environment. The present study aimed to evaluate the efficiency of ATZ removal from aqueous environments by using an anaerobic submerged biological filter in four concentration levels of atrazine and three hydraulic retention times. The maximum efficiencies of ATZ and soluble chemical oxygen demand (SCOD) were 51.1 and 45.6%, respectively. There was no accumulation of ATZ in the biofilm and the loss of ATZ in the control reactor was negligible. This shows that ATZ removal in this system was due to biodegradation. Furthermore, the results of modeling showed that the Stover–Kincannon model had desirable fitness (R2 > 99%) in loading ATZ in this biofilter.