Optimal Operating Condition of Substrate Removal in Oxidation Ditch Process with Intermittent Aeration

Abstract

An oxidation ditch can be used for the simultaneous removal of organic carbon and nitrogen compounds, as a relatively small scale wastewater treatment process. In this study, substrate removal and its optimal operating conditions in an oxidation ditch process with intermittent aeration was investigated through the treatment tests of synthetic sewage, and the theoretical model system combining the kinetic models of substrates removal with the tank-in series model of mixing. In the treatment tests, over 93% of T-N could be removed under the optimal condition of the intermittent aeration without decreasing the BOD removal efficiency compared with continuous aeration. Even under the worst condition of intermittent aeration, 72.5% removal of T-N obtained, whereas T-N removal under continuous aeration was less than 60%. Therefore, it was concluded that an efficient and stable simultaneous removal of organic carbon and nitrogen compounds is possible by selecting and keeping the best condition of intermittent aeration. Also, the theoretical model gave good agreement with the experimental data, and then proved to be applicable for predicting the quality of effluent from an oxidation ditch with intermittent aeration. By another computation using the model, the simultaneous removal of over 95% of BOD and over 90% of T-N was expected under the operating conditions which gave the value of 2 to 4 (mg/l) to the index OCM proposed to evaluate the total amount of oxygen supplied in a retention time.