A. H. AL-Abdaly, A., & K. K. Al-Ahmady, D. (2014). Effect of the hydraulic detention time and the volumetric ratio of anaerobic to aerobic zone on the efficiency of the upgraded activated sludge units using (Bardenpho) system. Al-Rafidain Engineering Journal (AREJ), 22(1), 97–109. https://doi.org/10.33899/rengj.2014.87020