Comparison of technical and economic efficiency of extended aeration and sequencing batch reactors processes in hospital wastewater treatment

Wastewater of hospitals can cause many risks to public health due to having a variety of pathogenic microorganisms, pharmaceutical substances, and other hazardous toxic substances. The aim of this study was to evaluate the chemical quality of effluents from wastewater treatment plant of Falsafi Hospital and Hakim Jorjani Hospital in Gorgan, Iran, and to compare them technically and economically. This descriptive-analytical study was performed on 64 samples of raw wastewater entrance and output effluent obtained from treatment plants using extended aeration process and sequencing batch reactors (SBR) in two hospitals in Gorgan. All experiments for determination of pH, free residual chlorine, biochemical oxygen demand (BOD), chemical oxygen demand (COD), and total suspended solids (TSS) were performed using standard methods. Finally, the obtained data were analyzed using t-test and Mann-Whitney test in SPSS software. Based on the results, the removal efficiency of BOD, COD, and TSS of the extended aeration system was 91, 90.8, and 95.7 percent, respectively, while these values for the SBR system were found to be 91.7, 91.9, and 95.3 Percent, respectively. Moreover, in the output of the two hospitals, pH values were recorded as 6.69 ± 0.26 and 7.33 ± 0.2 and the average amount of free residual chlorine was 0.12 and 0.13 mg/l, respectively. This study demonstrates good performances of the extended aeration activated sludge system and the SBR system in terms of reduction of pollution load to its standard limits for agriculture and irrigation purposes. However, due to slightly better efficiency, lower cost of investment, and operation compared to other methods, the SBR system is recommended.