A Model Construction For A Cyclic Activated Sludge System (CASS) System And Control Mechanisms Research Of Its Biochemical Reactiono Process

The cyclic activated sludge system?CASS?is a batch biological wastewater treatment technology that initially developed by Goronazy and his co-workers in the United States with the advantages of less filamentous bulking,low investment,simple operation and so on.So far,a large number of sewage treatment plants have employed this system at home and abroad.However,when facing the problems of suddenly fluctuating influent COD/N and increasingly stringent sewage discharge standards,CASS system could not develop effective strategy timely since its design and operation often depends on the experience of engineers,ultimately leading to a decrease in pollutants reduction.Therefore,the key research in this paper is to optimize the operating parameters of the CASS system,and create an effective mathematical model as a supplementary tool which is able to research the influence of the operating parameters on effluent quality in CASS system,in order to improve the sewage treatment performance of the system.The operating parameters?organic load?sludge age and temperature?used for the simulation of a lab-scale CASS system at different influent COD/N condition are determined by the response surface model?RSM?.The results showed under the suitable operation parameter combination,CASS system would operate at a good condition,resulting in meeting the simulation requirements.In addition,the volume ratio of the anoxic zone to the aerobic zone?VRZ?at different influent COD/N condition are researched by experiments.It is shown that under the VRZ condition of 0⁹/26,CASS system would work at best state,which can be used for the follow-up experiments and simulation of the objects.In order to study the effect of the operation parameters on the pollutants reduction.This study was to establish two mathematical model namely E-ASM1and M-ASM3 model by embedding competition mechanism between microbes,the formation and degradation kinetics of microbial products(i.e.,S_MPP and X_EPS)and the concept of simultaneous utilization and storage of organic substrate into the ASM1and ASM3 model,in order to describe the pollutants removal process in CASS system.Based on the result of sensitivity analysis,the sensitivity parameters were calibrated by using experimental data taken from a bench-scale CASS system.In addition,the applicability and accuracyof the two established model were evaluated,the result shown that the average deviation between the M-ASM3 model and the measured data of a pilot-scale CASS system is the smallest,demonstrating that this model was preferable to describe the biochemical reaction process in a CASS system.By comparing the output of the original ASM3 model,it is proved that the dynamic parameters of M-ASM3 model must be adjusted in order to describe pollutants concentration variation.The microbiological community structure in a CASS system was also detected,and it results show that the abundance of denitrifying bacteria is about 0.5 to 0.6 of that of aerobic heterotrophic bacteria.It is reasonable to use two different values to describe the growth rate of heterotrophic bacteria under aerobic and anoxic conditions namly?_NO=0.6,and proving the validity of the M-ASM3 model again.Effects of the working conditions?OLR???T and VRZ?on biochemical reaction kinetics in CASS system under different influent COD/N condition is studied by using M-ASM3 model.The simulation results show that the impact of the specific growth rate?_A.O.O of autotrophic bacteria under low influent COD/N condition is more significanter than that of the specific growth rate?_H.O.O of heterotrophic bacteria.The parameter H?the coefficient associated with the effect of substrate concentration?of them are 1.602gS_NH/m³.d and 0.925gSs/m³.d,respectively.While the influence of the specific growth rate(?_H.O.O and?_A.O)under high influent COD/N condition is opposite.The lower the influent COD/N condition is,the high the impact of the temperature,whereas the impact of the temperature on?_A.O.O is more smaller.In addition,the relationship between operating parameters and effluent quality in a CASS system are simulated.It is shown that the effect of working conditions on sewage treatment is the performance of parameters(?_H.O??_A.O?K_CODOD and K_NH)variation.Namely,increasing the values of these parameters could enhance the specific growth rate(?_H.O.O and?_A.O)and pollutant degradation rate constants(K_CODOD and K_NH),and then improve the effluent quality.