| dc.description.abstract | The objectives of this study are listed as follows: (1) to establish a mathematical model based on the kinetic of Activated Sludge Model No.1(ASM1) to describe the water quality variations in the sewer systems, (2) to establish a modified mathematical model based on the kinetic of Activated Sludge Model No.2d (ASM2d) and Mixed Culture Biofilm Model (MCBM) to describe the transformation of different compounds including carbon, nitrogen, and phosphorus in the A2O, TNCU, TNCU1, AOAO and TNCUO processes, (3) to explore the consistency between the calculated and observed values of different components by the modified model under different operation conditions in the processes, and (4) to analyze the kinetics of different microorganisms including heterotrophic organisms(XH), phosphorus accumulating organisms(XPAO), and autotrophic organisms(XAUT) in the processes by using the mathematical model.
In the study of establishing the sewer water quality model, oxygen transfer and water quality variations in gravity sewer pipes were studied in a 21 m long, 0.15 cm diameter model sewer. A partial differential equation that considered the Fick’’s law including the molecular and eddy diffusion terms were derived. The analytic solution of the partial differential equation was used to determine the oxygen transfer function values in the vertical direction by the method of nonlinear regression. The oxygen transfer function in the vertical direction is a function of molecular diffusion, eddy diffusion and flow velocity. In the experiments of the water quality variations in sewer pipe, the model values test values showed a good consistency. The results indicated that the biofilm attached on the pipe bottom predominated the degradation of pollutants. The anoxic growth of XH affected the transformation pathways of different components. XAUT did not exist in the system.
In the study of establishing the nutrient removal activated sludge model, there were three modifications: (1)the biosorption effect of the soluble COD(SS), (2)the ammonification of the organic nitrogen in influent wastewater, and (3)the XH growth in the anaerobic tank. The influent wastewater qualities were fixed and the operation conditions were varied. When a steady state was reached, the comparisons between the model predicted values and measured values in each test were made in five types of processes. It showed a good consistency between them. According to the consistent results, the biosorption effect of SS and ammonification of the organic nitrogen in the influent wastewater were the important effects in activated sludge system. Additionally, the XH might grow in the anaerobic tank. Furthermore, it was indirectly proved that the denitrifying PAOs existed in the nutrient removal activated sludge system.
In A2O, TNCU, and TNCU1 processes, the XH, XPAO, and XAUT would decrease in the anaerobic tank due to the lysis reactions and would increase in the aerobic tank. The polyphosphate (XPP) would decrease in the anaerobic tank and increase in the consequent aerobic tank due to the recovery of XPP level. At last, XPP revealed stable values under different operation conditions. The polyhydroxy-alkanoates (XPHA) would increase in the anaerobic tank and be consumed in the consequent aerobic tank. The concentration of XPHA maintained stable values eventually. On the other hand, the biofilm kinetic characteristics in TNCU1 process was modeled by using ASM2d and MCBM. The results indicated that when dissolved oxygen concentrations increased in the aerobic tank, the fraction of XAUT and nitrate would increase, the fraction of XI and ammonia nitrogen would decrease in the biofilm. The fraction of XH and SS in biofilm would not be affected when dissolved oxygen varied in the aerobic tank.
The nitrogen and phosphorus were removed efficiently in the TNCUO and AOAO processes by compartment reconfiguration and stepwise feeding strategy. The results obtained in this study can be summarized as follows: (1)The effective removal efficiency of carbon, T-P and T-N at 86.8~97.6, 92~100 and 62.9~76.4 %, respectively, were achieved in these testing runs. (2)The microbial kinetics would be affected by different operations. (3)When the step feeding strategy was adopted, the HRT was longer due to the less influent flowrate in the front stages and the microbes would grow in quantities in the aerobic reactors. In the followed anoxic reactors, the microbes would decrease in quantities due to the dilution effect. (4)The TNCUO and AOAO processes could be operated more efficiently without additional energy for nitrified liquid circulation and addition of external carbon substrate for denitrification in the anoxic zones.
Since the model simulation results showed a good consistency with the test values, the model could be applied on operations of the full scale plant. | en_US |