Study On Numerical Simulation And Optimization Of A₂N-SBR Two-sludge Denitrifying Phosphorus Removal System

With the improvement of emission standards of urban sewage treatment plants,the application of biological nitrogen and phosphorus removal process with high efficiency and low energy consumption is particularly important in the new sewage treatment plants and the upgrading of existing sewage treatment plants.The traditional biological nitrogen and phosphorus removal process usually has many problems,such as insufficient carbon source,dissolved oxygen contradiction,sludge age contradiction.A₂N two-sludge denitrifying phosphorus removal process has the unique advantages of typical"two-sludge system"and"one-carbon dual-use",which can solve the above problems.The process involves a multi-phase reaction process.The research on the mechanism of denitrifying and phosphorus removal only depends on experiments,which is a large workload.The mathematical model of activated sludge can simplify the complex activated sludge system reasonably according to the mechanism and realize the simulation of the system.It has the characteristics of high efficiency and low cost.It is an important tool to assist process design,process control,and parameter analysis.In this paper,the ASDM model is used to simulate A₂N two-sludge denitrifying phosphorus removal system,combined with experimental data,calibrate and optimize the process parameters,and provide technical support for the process optimization and expanded application of the A₂N two-sludge denitrifying phosphorus removal system.In this paper,the domesticated denitrifying phosphorus accumulating sludge and nitrifying sludge were successfully enriched,and A₂N-SBR two-sludge denitrifying phosphorus removal system was operated.a two-step method was used to enrich and acclimate denitrifying phosphorus accumulating sludge.In the first step,anaerobic/aerobic operation was conducted alternately.The phosphorus removal rate of aerobic phosphorus accumulating bacteria increased from 0.58%to 91.04%.In the second step,anaerobic/anoxic/aerobic operation was conducted alternately.The anoxic time is gradually extended,the aerobic time is shortened,and the dosage of nitrate-nitrogen is correspondingly increased.the proportion of anoxic phosphorus uptake in total phosphorus uptake increased from 15.4%to 95%.There was a significant linear relationship between COD absorption and TP release in the anaerobic stage,and between NO₃^--N removal and TP absorption in the anoxic stage.Indicating that there were a large number of denitrifying phosphorus accumulating organisms with NO₃^--N as the electron acceptor in the system,and the denitrifying phosphorus removal sludge was domesticated successfully.The enrichment of nitrification sludge was carried out by increasing the NH₄⁺-N load gradually.The removal rate of NH₄⁺-N was over 98%,and the NO₃^--N production rate was more than 85%.The removal of NH₄⁺-N and NO₃^--N production showed a good positive correlation during the cycle,and the nitrification was completed in 390 min.After the operation of the A₂N-SBR two-sludge denitrifying phosphorus removal system is stable,the removal rate of COD,NH₄⁺-N,TN and TP reach 86.13%,93.23%,75.97%,90.33%respectively,which achieves good COD removal and denitrification and phosphorus removal effect.The three SBR models with effective volumes of 5 L,45 L,120 L have high simulation accuracy after correction.The key parameters that needed to be corrected for the three nitrification systems were basically the same,which were Kinetic-Ammonia oxidizing-Max.spec.growth rate,Kinetic-Nitrite oxidizing-Max.spec.growth rate,Kinetic-Nitrite oxidizing-Substrate（NO₂）half sat.,Kinetic-Ordinary heterotrophic-Max.spec.growth rate,Stoichiometric-Ammonia oxidizing-Yield,Stoichiometric-Nitrite oxidizing-Yield.After sensitivity analysis and parameter adjustment,seven kinetic parameters and two stoichiometric parameters were corrected.After correction,the model can fit the four indexes of NH₄⁺-N,TN,COD,and TP well.The absolute error of steady-state simulation is less than0.5 mg/L,and the relative error is less than 5%;The mean relative error of dynamic simulation is less than 20%,and the mean absolute error and root mean square error are less than 4 mg/L.Based on the corrected model,the operation optimization simulation of the A₂N two-sludge denitrifying phosphorus removal system was carried out.Considering the effluent quality and system energy consumption,it was suggested that the dissolved oxygen concentration of the nitrifying unit should be set at 2 mg/L,the nitrifying sludge reflux ratio should be 20%,and the excess sludge reflux ratio and denitrifying phosphorus removal sludge reflux ratio should be25%.A₂N two-sludge denitrifying phosphorus removal system has a strong tolerance to a low-temperature environment in winter and can realize stable operation under annual temperature change.