No description available.

No description available.

The effect of low pH on autotrophic ammonia oxidation was to be investigated. Autotrophic ammonia oxidisers were successfully isolated from soils of low pH, from sites around Scotland, in an attempt to determine if acid tolerant or acidiphilic strains were responsible for nitrification in these soils. No acid tolerant bacteria were isolated and adaptation, of nitrifiers, to low pH was not found to have occurred during the maintenance of agricultural soil plots at low pH. Carbonate was found to be limiting at low pH, if sodium carbonate, alone, was used to adjust the pH of the medium. The pH minima for ammonia oxidation was not affected by additional carbonate. Recently isolated nitrifying bacteria, grown in liquid culture, were found to produce large amounts of exopolysaccharides at stationary phase, causing cell aggregation. Evidence suggested that this material offered protection against desiccation. Continuous flow columns were used to study surface attached N. europaea at low pH. It was demonstrated that surface attachment allowed nitrification to occur at 1.3 pH units lower than in liquid batch culture. This system also demonstrated a requirement for additional carbonate in medium of low pH. Evidence was found to indicate that ammonium is transported into the cell and that NH3 is not a limiting factor due to low pH. A nitrifying biofilm showed that attachment within a polysaccharide matrix offered significant persistence in a low pH environment and that activity occurred at a value lower than in liquid batch culture. The sensitivity of N. europaea to inhibition by PEX was found to increase in liquid batch culture. Continuous flow soil columns showed nitrapyrin to be more inhibitory at low pH. Nitrification occurred in columns at a pH value lower than in liquid batch culture. This culture system suggested that the bacteria were in a different physiological state than when grown in batch culture. Several strains of ammonia oxidisers, isolated from acid soils, were shown to possess a urease enzyme. A Nitrosospira sp exhibited limited growth on urea at pH 5.5.

No description available.

No description available.

Bibliography: leaves 77-83.

Graduation date: 1995

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.

The greenhouse gas nitrous oxide (N2O) is produced mainly by the microbial processes of nitrification and denitrification. I hypothesized that microbial community structure (composition and abundance) is linked to differences in soil N2O emissions from these two processes. Microbial community composition (type and number of nitrifier and denitrifier genotypes), abundance and N2O emission activity were determined and compared for soils from two landscapes characteristic of the North American prairie pothole region (cultivated vs. uncultivated wetlands). The landscape difference in composition of individual microbial communities was not predictive of soil N2O emissions, indicating that there is redundancy in each microbial community in relation to N2O emission activities. However, community factors influenced the pattern and distribution of N2O emission from the soils of the study site. For example, nitrification was the dominant N2O emitting process for soils of all landforms. However, neither nitrifier amoA abundance nor community composition had predictive relationships with nitrification associated N2O emissions. This lack of relationship may be a consequence of using amoA as the gene target to characterize nitrifiers. For denitrifying bacteria, there was a temporal relationship between community composition and N2O emissions. However, this may be related to the change in water-filled pore space over time. Alternatively, the presence of fungi can be linked directly to N2O emissions from water accumulating landform elements. Under hypoxic conditions, there may be two fungal pathways contributing to N2O release: fungal denitrification via P450nor and fungal heterotrophic nitrification. Results suggest that the relative importance of these two processes is linked to root exudates such as formate. It is the interaction between the seasonal fluctuations of the microbial and environmental factors that determine the level of N2O emissions from soils.

The greenhouse gas nitrous oxide (N2O) is produced mainly by the microbial processes of nitrification and denitrification. I hypothesized that microbial community structure (composition and abundance) is linked to differences in soil N2O emissions from these two processes. Microbial community composition (type and number of nitrifier and denitrifier genotypes), abundance and N2O emission activity were determined and compared for soils from two landscapes characteristic of the North American prairie pothole region (cultivated vs. uncultivated wetlands). The landscape difference in composition of individual microbial communities was not predictive of soil N2O emissions, indicating that there is redundancy in each microbial community in relation to N2O emission activities. However, community factors influenced the pattern and distribution of N2O emission from the soils of the study site. For example, nitrification was the dominant N2O emitting process for soils of all landforms. However, neither nitrifier amoA abundance nor community composition had predictive relationships with nitrification associated N2O emissions. This lack of relationship may be a consequence of using amoA as the gene target to characterize nitrifiers. For denitrifying bacteria, there was a temporal relationship between community composition and N2O emissions. However, this may be related to the change in water-filled pore space over time. Alternatively, the presence of fungi can be linked directly to N2O emissions from water accumulating landform elements. Under hypoxic conditions, there may be two fungal pathways contributing to N2O release: fungal denitrification via P450nor and fungal heterotrophic nitrification. Results suggest that the relative importance of these two processes is linked to root exudates such as formate. It is the interaction between the seasonal fluctuations of the microbial and environmental factors that determine the level of N2O emissions from soils.