Chapter I presents general information about landfill leachate, characteristics of leachates in Vietnam and review of general leachates treatment situation in the country.
In chapter II, a careful bibliographical study on biological processes of nitrification and denitrification is done.
In chapter III, existing activated sludge models are briefly reviewed, focusing on ASM1 and ASM3. The ASM3 model then is studied in more detail with focuses on state variables, processes; kinetic and stoichiometric parameters of the model.
A careful bibliographical study on sequencing batch reactor (SBR) is done in chapter IV. Chapter V presents materials and methods that will be applied in the experiments in laboratories and modelling processes of this study.
In chapter VI, an SBR bench-scale is set up in the laboratory to study partial nitrification process.
Chapter VII presents the experimental studies on maximum nitrification and denitrification capability, then determination of kinetic and stoichiometric parameters that will be used for calibration in the next steps.
Chapter VIII presents a study on partial nitrification by applying data analysis and experimental planning method.
In chapter IX (the key part of the Thesis), the modelling of the partial nitrification and denitrification in SBR is presented.
It is hoped that, this study will contribute to the major issue of leachate treatment in Vietnam, especially in the North of the country where leachate characteristics and variations are the same as what was used during our experiments.
Partial nitrification seems to be easily achieved in an SBR bench-scale using leachate in Nam Son landfill site. Some important characteristics of the studied leachate, are high alkalinity, high pH leading to high free ammonia concentration in the system. This free ammonia is known as a growth rate inhibitor for nitrite oxidizing bacteria, thus limiting oxidation of nitrite to nitrate and accumulating nitrite during the nitrification period. DO concentration is also known as an important influencing factor in partial nitrification in many previous studies. But in our case, its influence is just significant when the nitrification process is nearly complete: no more ammonium remains in the system, alkalinity concentration is reduced leading to a lower buffer capacity, lower pH, and then nitrite is easily oxidized to nitrate. A sufficiently high DO concentration in this case, expresses its importance in bringing about the best nitrification efficiency, while saving aeration energy.
The SBR technique has demonstrated its advantages, especially the flexibility in changing the working volume, and the operating time.
Modeling of partial nitrification and denitrification processes for landfill leachate treatment using the SBR technique was the main objective of this study. The simulation software - WEST® program was very useful tool to implement this task. With this program, the available model base for activated sludge model (ASM1, ASM 2, ASM 3 etc,), presented in the Peterson matrix, the variables, kinetic, stoichiometric parameters, processes can be easily modified to another activated sludge model suitable in the scope of our study. In the present case, based on the ASM3, the ASM3_2step was developed and applied, in which nitrification and denitrification are divided into two steps with nitrite as an intermediate product. The modified ASM3_2step has shown its high accuracy during calibration process. It could be use also for the other processes/techniques using activated sludge, by adding more equations and parameters.
Calibration and validation were implemented for two cases: Partial nitrification and denitrification with and without carbon addition. Good results were obtained where the simulations fit well the experimental data. The kinetic and stoichiometric parameters found are very important for the other simulations, especially in process optimisation.
It also demonstrates that, through process optimisation, general productivity of the SBR system can be increased. Controlling DO, changing operating time cycle mechanisms can improve the total nitrogen removal efficiency, save some aeration energy for nitrification and carbon source for denitrification.
As our results are very promising, the next step could be to implement the ANAMMOX process.
Key words: Partial nitrification and denitrification, ASM3_2steps, SBR, modeling.