In this research, four experimental plants have been constructed and operated in order to study the impact of using the anaerobic selectors on the behavior and efficiency of the extended aeration activated sludge system. The study program was divided into three stages. In the first stage, the experimental plants were run on the hydraulic retention time of the aerobic reactor equals to (32) hours, whereas, the hydraulic retention times in the biological aerobic reactors for the second and the third stages were (24 and 18) hours respectively. The results of the study revealed that; adding the anaerobic selectors improves the properties of the aerobic biological treatment in terms of removing soluble organic materials (CODs) and the efficiency of removing phosphor (PO4). The results also showed that,the organic and phosphorus removal efficiency increases with increasing the hydraulic retention time of the anaerobic selector. In contrast the values of the sludge volume index (SVI) decreases with this increasing. Higher removal efficiencies were recorded in the experimental stations that include anaerobic selector, which operates on a hydraulic retention time of (120 min) followed by the plant with the selector of (60 min) detention time and in the last place the plant that include selector, which operates on a hydraulic retention time of (30 min).
Keywords:Anaerobic selector, Activated sludge, HDT,SVI, Phosphorus removal, Organic removal