| Abstract | In this study, two pilot scale aerated biological reactors using charcoal as submerged media were conducted to determine the optimum HRT that affects the removal efficiency. The average size of charcoal was 5-10 cm. Influent used was AIT domestic wastewater and air was supplied to maintain dissolved oxygen concentration more than 3-4 mg/lat 0.5m from inlet. BOD removal efficiencies at steady state were 65.1, 89.7 80.1 and 92.6 % for HRT 4, 6, 8 and 10 hours, respectively. TKN removal efficiencies at steady state were 26.4, 88.4, 87 .3, 86.2% for HRT 4, 6, 8 and 10 hours, respectively. The organic loading rates were 140, 113, 73, and 42 g. BOD/m3 .d for HRT 4, 6, 8, and 10 hours. The removal efficiencies of SS, VSS, BOD, S.BOD, TKN and NH4-N were almost same at HRT 6, 8, and 10 hours and those was larger than of HRT 4 hours. Thus, it was concluded that the optimum HRT was more than 4 hours. The wastewater quality parameters were measured along the reactor at the steady state. It showed that pollutants were removed mainly in the first-half of reactor. The results of batch test for nitrification and denitrification confirmed the occurrence of both biological reaction in all part of the reactor. The removal efficiencies of fecal coliform were 92.85, 96.57 and 99.74% for HRT 4, 6 and 10 hours, respectively. Coliphage removal efficiency were 86.7, 90.0 and 80.0% for HRT 4, 6 and 10 hours. It can be concluded that the removal efficiency of fecal coliform and coliphage were more than 90 % and 80 % , respectively. The numbers of fecal coliform and coliphage in influent were about 8*106 MPN/ lOOml and 3*102MPN/100ml, respectively. |