Abstract
The evaluation and consideration issue on BOD removal was studied by using observed data in rural sewerage facilities with biofilm processes. It was found that the probability distribution of influent BOD concentration in inflow pump tank and effluent BOD·EATU-BOD concentrations in sedimentation tank agreed with logarithmic normal distribution. the 130D removal was confirmed to be satisfied with treatment performance required. It was recognized that the distribution of effluent BOD concentrations in sedimentation tank has wider variation than the distribution of influent BOD concentration in inflow pump tank because of N-BOD concentration due to nitrification. The increase of effluent BOD concentrations in sedimentation tank was found to be resulted from the oxygen required for the conversion of ammonia to nitrate in effluent and dilution water. It was considered that the measured BOD value cloud be achieved to meet the C-BOD value due to the suppression of nitrification reaction by changing the sampling point from sedimentation tank to disinfection tank or discharge tank. From an analytical standpoint of the evaluation method regarding to BOD removal, the improvement of existing BOD test such as change of standard dilution water method and sampling point is the effective measure to overcome the effect of nitrification in rural sewerage facilities with biofilm processes.
