en عمومى General پژوهشي Research <strong>Background:</strong> Various chemical, physical and biologic treatment methods are being used to remove nitrogen and phosphorus from wastewater. Sequencing batch reactor (SBR) is a modified activated sludge process that removes phosphorus and organic material from sanitary wastewater, biologically.<br> <strong>Methods: </strong>This study was conducted in 2016.The performance of an aerobic-anaerobic SBR pilot device, located at Ahwaz West Wastewater Treatment Plant, Ahwaz, southern Iran in phosphorus and organic material removal was evaluated to determine the effect of the aerobic-anaerobic step time on the efficiency of nitrogen and phosphorus removal, the effect of changing the sequence of steps and the effect of time ratio on phosphorus removal efficiency. A reactor of 8 L was used. Influent contained 397 and 10.7 mg/l COD and phosphorus, respectively. The pilot plant started with a 24 h cycle including four cycles of 6 h, as follows: 1- Loading (15 min), 2-Anaerobic (2 h)-Aerobic (2 h), 3- Settling (1 h), Idleness (30 min) and 5- decant (15 min).&nbsp;<br> <strong>Results: </strong>After reaching steady conditions (6 months), Removal percentages of phosphorus, BOD₅, COD, and TSS in The SBR over a period of 6 months was 79%, 86%, 89% and 83%, respectively.<br> <strong>Conclusion:</strong> Result of this study can be used for designing and optimum operation of sequencing batch reactors. Environment, Phosphorus, SBR, Wastewater 27 32 http://ijt.arakmu.ac.ir/browse.php?a_code=A-10-483-1&slc_lang=en&sid=1 Nadiya Shahandeh 10031947532846007289 0000000306947361 No Department of Environmental Engineering, Ahvaz Branch, Islamic Azad University, Ahvaz, Iran. Reza Jalilzadeh Yengejeh rahma.reza@gmail.com 10031947532846007290 0000000283605739 Yes Department of Environmental Engineering, Ahvaz Branch, Islamic Azad University, Ahvaz, Iran.