In recent decades, there has been increasing interest in wastewater treatment because of its direct impact on the environment and public health. Over time, other forms of treatment have been developed and modified, including extended aeration. This process is included in the suspended growth system. In this paper, a comparative study was conducted between the efficiency of the extended aeration plant and that of the trickling filter plant in removal of BOD and COD. The method of comparison was done by knowing the value of the pollutant before and after the treatment and then extract the removal ratio of each pollutant within each plant. The results showed that the percentage of removal of BOD in the trickling filter was 79.5% while in extended aeration was 90.7%. The efficiency of COD removal was 60% in trickling filter and 86% in extended aeration. The study was carried out at the Barrakiyah WWTP in Najaf province in Iraq. As the plant contains these two types of treatment, and the study has been achieved through monthly examinations over a full year.
