Study On Hydrodynamic Characteristics And Optimal Operation And Control Of Modified Oxidation Ditch

In order to solve sludge deposit in the bottom,low nitrogen removal efficiency of the modified oxidation ditch in Western Wastewater Treatment Plant in Handan city,the hydrodynamic characteristics and optimal operation and control in full-scale were studied in this paper.Considered anoxic zone of the oxidation ditch as the experimental ditch,the velocity were tested at the different conditions such as when only the aerating dish[single speed/double speed(with high or low velocity) or submersed flow driver and both of them running,results of velocity distribution figures in kinds of states were gained. There all existed high velocity in upper and intermediate,low velocity in below and bottom.And the flow pattern in crook ditches were very complex,there all existed high velocity outside and low inside,intermediate high,both upper and below low in kinds of crook ditch.And meanwhile there all existed sludge deposit in straight and crook ditches,on the basis of which,according to the devices arrangement and test results,the experimental ditch was divided into three parts by the submersed flow driver,as follows: RD04～RD11(east),RD11～RS09(east),RS09～RD04(west),and then the optimal combination modes of aerating dishes and submersed flow driver were obtained by experiment design,and the feasibility was proved by experiment finally.The results revealed that the flow pattern in straight and crook ditches both had been improved obviously after the states adjusted,although there existed sediment 0.3～0.8m,0.4～1.2m (mainly existing in the forth crook ditch),respectively,which made it exist dead sludge because of the previous scheduling by experience and not removed in short time,and it can be inferred that the below velocity were 0.14～0.27m/s,0.11～0.23m/s,respectively.On the basis of the above work,according to the experimental study and analysis of synchronous nitrogen and phosphorus removal by the oxidation ditch,it can be concluded that COD_Cr removal efficiency changed slightly before and after the states adjusted,90.70%,91.04%,respectively,COD_Cr concentration in effluent were always below 70mg/L.Compared to the states before adjusting,NH₄⁺-N and TN removal efficiency after adjusting were both increased by 11.57%,11.28%,respectively,and after adjusting average TP concentration in the effluent is 0.50mg/L,the TP removal efficiency was 93.93%,the processes of anaerobic phosphorus release,anoxic and aerobic phosphorus adsorption occurred.The optimal control parameters for COD_Cr,TN and TP removal were determined through orthogonal experiment of intuitive and variance analysis.The significant factors of COD_Cr and TN and TP removal by the modified oxidation ditch were DO and MLSS,DO,MLSS and R,respectively.The optimal operation parameters were determined as follows:DO concentration of anoxic and aerobic zone of 0.3～0.5 mg/L,2.0～2.5mg/L,respectively,MLSS concentration of 5000mg/L,sludge recycle flow rate of 65%.The nitrogen and phosphorus removal by the modified oxidation ditch depended on the control on DO concentration,DO concentration in anoxic and aerobic zone of oxidation ditch were 0.3～0.7,2.0～3.2mg/L,respectively.MLSS in the oxidation ditch should be controlled seriously,optimal MLSS concentration of 4600～5400mg/L,the control range of F/M was 0.06～0.13[kgBOD/(kgMLSS·d)],and sludge age was 16～20d through the discharge of residual waste.