Application Research Of Modified ASM-CFD Coupling Simulation In MBR Operation And Condition Optimization

In this paper,the actual membrane bioreactor(MBR)of a biopharmaceutical wastewater treatment facility in Pudong,Shanghai was used as the research object,and the coupled model of modified activated sludge No.1 model(ASM1)-computational fluid dynamics(CFD)was applied to the simulated MBR.The operation situation,in order to obtain the MBR flow field with the biochemical reaction model added.The MBR water inflow and operating conditions of the actual operation of the project are used as model parameters,and the effluent data is used for model verification.The modified ASM1-CFD coupling model can accurately simulate the water quality indicators such as COD and ammonia nitrogen in MBR for the characteristics of sludge in MBR,and better display the membrane fouling.The research contents are as follows:(1)ASM1 model coupled with CFD model MBR simulation: ASM1 model is applied in the simulation.The simulation in MBR increases the process of biological reaction,making the simulation operation of the reactor more similar to the actual project.Because of the addition of the biological reaction process,in addition to the hydraulic indicators of the effluent,the biological indicators can better compare the degree of conformity of the model with the actual operating conditions.The ASM model parameters at the time of simulation refer to the actual and partial empirical values,and the influent velocity and bottom aeration intensity are consistent with the actual engineering.(2)Revise the ASM1 model and add the effect of SMP on the biological response.The coupled ASM1-SMP model was used to analyze the degradation of COD,total nitrogen and ammonia nitrogen in the MBR.(3)Using the modified ASM1 model to simulate the effects of different MLSS on the effluent quality under aeration intensity.Exploring the influence of the inlet concentration on the effluent water quality,and determining the threshold of the influent COD and total nitrogen concentration leading to the effluent quality exceeding the standard.(4)Using the modified ASM1-CFD to simulate the MBR operating conditions to explore the membrane fouling.Under the premise of ensuring the same aeration intensity,the surface contamination degree of 8mm and 10 mm flat film membrane spacing is simulated and analyzed,and the membrane spacing for effective membrane fouling is sought.Under the condition of ensuring the position of the membrane module is unchanged,the experiment is 100-180m3/L.The surface contamination of the membrane under five aeration strengths was explored to determine the aeration intensity suitable for membrane fouling.The accumulation of membrane surface contamination under different sludge concentrations was investigated to provide data for later conditions optimization.Through MBR meshing,correction of coupling,calculation and result output of ASM1-CFD model,the following conclusions are drawn:(1)Applying the ASM1 model to the CFD simulation of MBR,the MBR effluent water quality simulation results are compared with the actual engineering operation results: during the actual MBR operation,the COD effluent water quality is good,the removal rate is 89%,and the effluent concentration is far.Below the emission standard,the overall operating state is stable and good,and can be used as the basis for the modeling research of this topic.The effluent COD results and measured values of CFD simulations are about 11% overall,slightly higher than 10% in the literature.The overall COD value is low,and the model needs to be corrected.The total nitrogen effluent quality is good,the removal rate is 78%,and the effluent concentration is much lower than the standard.The total nitrogen of CFD simulation is in good agreement with the measured value,and the average gap is about 1mg/L,which is within the acceptable range.The MBR flow field analysis shows that since the aeration surface is disposed below the membrane module rather than the bottom of the reactor,the flow field near the membrane module is in good flow,the flow rate is high,and the gas-liquid mixing effect is good.The flow of the mixed liquid near the liquid level above the water inlet and the pre-zone on both sides of the bottom of the tank is poor,and belongs to the “dead zone” in the reaction tank.(2)The soluble microbial product(SMP)parameters were added to the ASM1 model to obtain the modified ASM1 model.The simulation results showed that the water COD was more consistent with the actual effluent,and the accuracy of the effluent prediction was better,with an error of about 5%.The total nitrogen content obtained by the model simulation showed no significant deviation from the ASM1 model.For the analysis of various indicators in the MBR pool,the removal efficiency of COD and ammonia nitrogen in the aerobic zone inside the reaction tank is high.The simulation of adding SMP components into the reactor is more accurate for COD simulation and has less effect on total nitrogen.When the concentration threshold of influent COD is about 650 mg/L,the effluent concentration exceeds the emission standard of 50 mg/L.When the concentration threshold of total influent nitrogen is about 40 mg/L,the effluent concentration is higher than the discharge standard of 10 mg/L.As the MLSS increased,the concentrations of effluent COD,total nitrogen and ammonia nitrogen decreased.The increase of aeration intensity promotes the degradation of COD and ammonia nitrogen.When the aeration intensity is 160 m3/L,the best degradation effect of COD is obtained.When the gas intensity is 140 m3/L,the effect of degrading ammonia nitrogen is most obvious.(3)Simulation of different membrane spacing and aeration intensity,the results show that the membrane spacing is increased from 8mm to 10 mm,which increases the fluid space between the membranes and reduces the membrane fouling on both sides of the membrane module.The degree of contamination of the entire membrane module is also reduced.The five aeration strengths of 100-180m3/L were simulated.The simulation results verified the influence of the intensity of aeration on membrane fouling.With the increase of aeration intensity,the membrane fouling was improved.However,the aeration intensity of 180 m3/L causes the sludge to break into small particles and release the EPS into the mixture,resulting in more serious membrane fouling.Therefore,a membrane spacing of 10 mm in the engineering MBR and an aeration intensity of 160 m3/L are effective methods for controlling membrane fouling.The analysis of membrane surface contamination under different sludge concentrations has a direct impact on the membrane fouling.The higher the MLSS concentration,the more serious the membrane surface contamination.In summary,in the MBR,the SMP parameters are added to the ASM1 model for correction,the ASM1 and CFD coupling are modified,and the simulation of the MBR operation is verified,and the simulation results are found to be closer to reality.The modified ASM1-CFD can predict the effluent water quality,the flow field distribution in the reactor,the reactor operating conditions,such as aeration intensity,membrane fouling,etc.,to provide a reliable prediction method for engineering operation,and also provide a simulation for controlling membrane fouling.reference.