| Since its original application in Holland,the oxidation ditch process has become a significant sewage treatment technique all over the world. Operating in the aeration mode,it can be obtain a high treatment efficiency together with a high degree of sludge stabilization.A general dynamic model,including biological process,hydraulics,oxygen transfer and temperature,was studied for the oxidation ditch. Transport of wastewater constituents was described by 1-D advection-dispersion. Equation with the source term written principally according to the Activated Sludge Model No.l(ASMl). Oxygen transfer was strongly related to the feature included in the oxygen mass balance. The temperature model was based on a heat balance of reactor.The model consists of mass balance equations for 13 water quality variables reported in the ASM1,boundary conditions are defined at the control volumes,where the inlet,the outlet,and the rotor are located. The model is applied to predict the concentrations of all the 13 water quality variables in the tripe oxidation ditch of Binhe WWTP,Shenzhen,performing carbon oxidation,nitrification,denitrification and settling. The application of the model shows that all variables,with the exception of dissolved oxygen(DO),are uniformly distributed in the ditch,thus permitting the characterization of the oxidation ditch as a completely-mixed reactor. The DO concentration,which controls the reactions rates of almost all the process,shows a plug-flow behaviour,In the calibration,the values of the correction factors a and 3 of the equation of the aeration equipment(rotors) have been determined. The application of the model shows that predicted DO concentration values are in a very good agreement with experiments. |
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