Performance Evaluation of the Extended Aeration Activated Sludge System in the Removal of Physicochemical and Microbial Parameters of Municipal Wastewater: A Case Study of Nowshahr Wastewater Treatment Plant

Introduction:&nbsp;Extended aeration activated sludge system has a lower sludge production than other activated sludge processes. Due to its high hydraulic retention time (HRT), the tolerance of this process is higher than the shocks caused by increased organic loading rate. The main objective of this study is to evaluate the performance of the aeration system in removing physicochemical and microbial parameters from the wastewater of Nowshahr, Iran. Materials and Methods:&nbsp;This is a descriptive-analytical study that was carried out in the wastewater treatment plant of Nowshahr during 6 months. The parameters BOD5, COD, TSS, total coliform (TC) and fical coliform (FC) were measured, and also the MLSS, F/M ratio, SVI, HRT and &theta;c were measured in aeration basin. Data were analyzed using the Excel software and SPSS (Pearson correlation test and one-sample t-test), and P < 0.05 was considered significance level. Results:&nbsp;The average removal efficiency of BOD5, COD, TSS, TC and FC was 57.7%, 61.4%, 70.8%, 84.6% and 84.3% respectively. The &theta;c, HRT, SVI, F/M and MLSS in the aeration basin were obtained, respectively, 5.64 day, 25 h, 48.83 ml/g, 0.28 day-1 and 180 mg/L. In addition, the average output of parameters in the hot months of the year was higher than those in the cold months. Conclusion: According to the results, the Nowshahr wastewater treatment plant has the adequate efficiency to produce effluent in accordance with environmental standards for discharge into surface water and consumption in agriculture.