| Oxidation ditch is the most widely used process for municipal wastewater treatment. The purpose of this paper is to investagate the actual effect of oxidation ditch process and to study the possible method to lower energy consumption for the operation of oxidation ditch. The change of the pollutant concentration in wastewater was analysed firstly along the flow from the influent to the effluent in No.3 WWTP of Xi’an city. Then, the activity of the sludge was measured through oxygen uptake rate, ammonium oxidation rate, nitrite oxidation rate, endogenous breathing rate, denitrifying rate, release and absorbing phosphorus rate. At last the concentration change of DO along the ditch and water head loss was measured and evaluated. The results indicate that:1、The removal efficiency of COD、NH4+-N、TN and TP can reach 94.9%、90.3%、79.8% and 93.8% respectively. Effluent water quality can meet the first standard （B） of《Discharge standard of pollutants for municipal wastewater treatment plant》. The Orbal oxidation ditch has signifcant effect on the removal of nitrogen and phosphorus.2、Sludge activity of nitrification and denitrification is strong. By comparing the method of oxygen uptake rate and ammonium oxidation rate, it showed that the oxygen uptake rate can represent ammonium oxidation rate, which is accurate,fast and simple.3、The characteristic of DO gradient change in single ditch and between ditches guarantees the optimum condition for the removal of nitrogen and phosphorus. To achieve favourable effect on nitrogen and phosphorus removal, it is necessary to control the number of aeration disc reasonably and maintain DO concentration at 01.5mg/l.4、In the premise of avoiding sludge sedimentation, the horizontal velocity of the flow could be reduced for decreasing water head loss in oxidation ditch, which can also cut down the energy of aeration and propulsion equipments greatly. So the operation costs of wastewater treatment plant will be saved. |
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