抄録
In this study, two municipal sewage treatment plants that employed modified oxidation ditch system for sludge reduction were assessed to evaluate its performance based on mass balance analysis. An analysis of operational records showed the peak of discharge during midnight due to the flow equalization effect. A preliminary study showed the higher organic concentration in effluent from modified system although the removal rate was almost same as that of the traditional oxidation ditch system. Mass balance analysis based on the round-the-clock survey revealed the removal rates of organic parameters, T-N and T-P were 84 - 98%, 64 - 78% and 54-87%, respectively. Of the two plants surveyed, the plant with lower treatment efficiencies in most parameters showed periodical carryover of SS, suggesting the high accumulation of sludge due to the lack of appropriate sludge withdrawal. Based on the mass balance analysis, it is estimated that the sludge production was reduced by ca.20% without the deterioration of effluent quality. To expect more reduction effect, it is necessary to find the optimum design and operational conditions of this system where the minimum withdrawal and maximum sludge reduction effect will balance.
