Abstract
The water quality before and after the secondary treatment in domestic wastewater treatment facilities in Chiba prefecture Japan were surveyed. T-N removal performance was high in the plants operated in intermittent aeration mode as compared with those operated in continuous aeration mode because of occurence of biological denitrification in their process. The performance of T-N removal was low in the facilities of which influent BOD concentration was low even though it was operated in intermittent aeration mode. The decease of BOD was observed in equalization tanks in the facilities of resort condominiums of which influent BOD load was extremely low. The mean value of influent BOD/T-N ratio in such facilites was below 2. That caused lack of proton donor resulting in difficulty in progress of denitrification while nitrification was advanced sufficiently. The relation between influent BOD/T-N ratio and T-N removal in surveyed 37 facilities suggested that the maximum T-N removal for a certain value of BOD/T-N ratio smaller than 4 decreased by the equation approximately: RN,Max=20×(BOD/T-N)+10, where RN,Max is the maximum T-N removal(%). This equation can be applied to estimate the amounts of proton donor to be added in facilities of which influent BOD/T-N ratio is low.
