Mathematical Modeling And Optimization Analysis Of Wastewater Treatment A~2/O Process

With the rapid development of urbanization in China,the quality of people’s lives has been rising,urban sewage discharge has to a new height,and sewage discharge standards are increasingly strict.The research on sewage treatment technology is in full swing.As an essential part of sewage treatment,it is vital to save operation costs under the premise of pollutants reaching the effluent standard.The activated sludge process stands out from the sewage treatment process because of its excellent treatment effect and low cost.In recent years,the application of activated sludge mathematical models combined with computer software in the design,optimization,and upgrading of sewage treatment plants has been expanding.In this paper,the A²/O process model of a sewage treatment plant in Kunming was established by using the ASM1 model in Matlab software,and the operation of the sewage treatment plant was simulated based on accurate operational data.The simulated results of BOD₅,TN,and NH₃-N fitted well with the measured results,and optimization suggestions were based on the original process parameters.The ASM1 model used in the research process was the ASMs series model of the beginning,including 13 components,5 stoichiometric coefficients,14 kinetic parameters,and 8 reaction processes,and the matrix form was expressed.The model was widely used in wastewater treatment plants at home and abroad because of its simple structure,clear rate expression,and great parameter values.It can be simulated by computer software flexibly.In this simulation process,the steady-state simulation of the actual sewage treatment plant in the dry and rainy seasons was carried out using the model.There was some error between the simulation results and the true water output value in the dry and rainy seasons.Sensitivity analysis was used to analyze the parameters,and the trial algorithm was used to correct the parameters that had a noticeable effect on the effluent results.Parametersμ_A（maximum specific growth rate for auto trophic biomass）,f _P（fraction of biomass leading to particulate peoducts）,Y_H（yield for hetero trophic biomass）,b _H（decay coefficient for heterotrophic biomass）,K_OH（oxygen half-saturation coefficient for heterotrophic biomass）,and K_NH（ammonia half-saturation coefficient for autotrophic biomass）,were repaired under dry season conditions.Rainy season correction under the state of the parameters of the b _A（decay coefficient for autotrophic biomass）,μ_A（maximum specific growth rate for auto trophic biomass）,b _H（decay coefficient for heterotrophic biomass）,Y_H（yield for hetero trophic biomass）,f _P（fraction of biomass leading to particulate peoducts）,K_OH（oxygen half-saturation coefficient for heterotrophic biomass）,K_NH（ammonia half-saturation coefficient for autotrophic biomass）.The corrected model had a small error and was applied to dynamic simulation.Under the premise of ensuring the quality of effluent water,a series of process parameters were optimized and analyzed to reduce energy consumption,including internal reflux ratio,external reflux ratio,sludge discharge,and dissolved oxygen.After analysis,the optimal internal reflux ratio in the dry season was 180%,the optimal external reflux ratio was 70%,the optimal sludge discharge was 634.4 m³/d,the optimal range of dissolved oxygen concentration was 1.1 mg/L-2.1mg/L,that is,the value of KLa in the fifth tank should be between 90/d-122/d.In the rainy season,the optimal internal reflux ratio was 160%,the optimal external reflux ratio was 70%,the optimal sludge discharge capacity was 1179 m³/d,and the optimal dissolved oxygen degree range was 0.9mg/L-1.9 mg/L,that is,the value of KLa in the fifth tank should be 74/d-106/d.The results show that the A²/O process mathematical model can reasonably simulate the natural change process of the sewage treatment plant,and the optimization suggestions can be used as a benchmark for simulation and optimization of other sewage treatment plants.