Abstract
The design and operation factors on the effluent ATU-BOD and N-BOD concentrations in sedimentation tank were investigated by using observed data in the rural sewerage facilities with biofilm process and activated-sludge process. The operational problems with occurrence of N-BOD were also studied on the basis of the results of BOD removal performance obtained from research data of the rural sewerage facilities with both processes. Regarding to effluent BOD concentrations in sedimentation tank with both processes, it was found that the biological nitrification reaction and nitrogenous compound had the considerable influence on the effluent N-BOD concentration in sedimentation tank. The effluent ATU-BOD concentration in sedimentation tank was assumed to be governed by first-order function with complete-mix system of biological treatment process in the rural sewerage facilities with both processes. It was recognized that the effluent ATU-BOD concentration in sedimentation tank with both processes were influenced by the design and operation factors such as influent ATU-BOD concentration, microorganisms (mixed liquor suspended solids/specific surface area of contact filter for fixed bed submerged filter), and average DO in reactor (contact aeration tank/aeration tank). The effluent ATU-BOD concentration in sedimentation tank with both processes were found to be predicted by the empirical formula of hydraulic retention time and the design/operation factors mentioned above. Consequently, it is important that the control in occurrence of N-BOD and operational countermeasure for decrease of ATU-BOD are effective to maintain BOD removal efficiency in the rural sewerage facilities with both processes.
