Activated Sludge Model Parameters Calibration Based On Improved Genetic Algorithm

The activated sludge has been widely used all over the world, with the advantages of wide processing range, high operating efficiency and strong anti-interference ability. A reliable mathematical model could predict the actural effluent index in sewage plant, playing an important role in technical study of activated sludge process. Nevertheless, there are some problems about the popularization and application of mathematical models of activated sludge, with a serious issue about the model parameter particularly.In view of the defects about precocity, slow convergence and poor capability in local search of the genetic algorithm, this paper put forward an improved genetic algorithm based on clonal selection strategy (Clonal Selection Genetic Algorithm, referred to as CSGA). CSGA was proved to be superior to the standard genetic algorithm by experiments on several test functions.In this paper, the development history and research status of activated sludge model and secondary sedimentation tank model were introduced firstly. Then the model of an Orbal oxidation ditch activated sludge process was set up based on ASM1and Takacs’s double index settlement rate of secondary sedimentation tank model. After some work about steady state simulation and dynamic simulation, the errors between the value of simulation and monitoring were calculated. The results showed that the errors of COD and TN were small, and the error of SNH was larger.The sensitivity analysis about stoichiometric parameters and reaction kinetic parameters were done in this model. Eleven parameters were calibrated by GA and CSGA dynamically, including Ya. YH,Koh/, ηg, μa, Knh, Kou, O2, O3and O4The errors between the values of simulation and monitoring were calculated, and the results indicated that the effect of calibration by CSGA was better than that by GA. The error decreased obviously after calibrating some parameters, and the accuracy of the model was also improved.Because of high concentration of TN effluent, the operation parameters and process parameters were optimized by CSGA in the model. After the optimization, the average concentration of TN reduced from18.82mg/L to12.91mg/L. and the exceeding standard rate reduced from97.7%to29.17%. The effect of optimization was obvious, and the waste water after processing could be drained off safely.