Evaluating the Performance of Activated Sludge System by Anoxic- Oxic Process: a Case Study in Mahdishahr

  Anoxic-oxic (A/O) is a new method of wastewater treatment and is being used in Mahdishahr wastewater plant. considering the lack of studies in this area, it seemed necessary to study the performance of A/O system in wastewater treatment. This study was carried out to evaluate the efficiency of Mahdishahr wastewater Treatment Plant. The present cross sectional study was conducted in 2014 during 8 months. Sampling was performed two times per week from the incoming wastewater, aeration pond and effluent. Overall, 200 samples were collected. The efficiency of Treatment Plant was measured by TSS, BOD5, COD, MLSS, MLVSS, and SVI indices in aeration ponds based on standard method. Then the datas were analyzed by statistical analysis. The mean concentrations of BOD5, TSS and COD in influent were 221.6 mg/l, 203.8mg/l and 321 mg/l respectively. The mean concentrations of BOD5, TSS and COD in effluent were 23.65 mg/l, 16.79 mg/l and 34.9 mg/l respectively. According to the results the average removal efficiency of BOD5, TSS and COD were about 87.25%, 91.77% and 87.29% respectively. These results are in accordance with standards of Iranian Department of Environment to be used for agricultural purposes. During the study, the monthly mean for SVI was 67.3 ml/g and the mean for MLSS and MLVSS was 1880 and 1182 mg/l respectively.   in present study, the efficiency of A/O process in COD removals is approximately 89 percent, representing high degradability of wastewater in A/O reactor. In addition, according to the results this method was efficient and the effluent complied with Iranian standards in terms of COD, TSS and BOD5, thus the flow is suitable for reuse or discharge to water courses.