Treatment wetlands play an important role in reducing nitrogen content in wastewater and agricultural run-off water. The main removal process is denitrification and the removal efficiency depends on the hydrological and microbiological features of the wetland, especially in terms of water residence times and denitrification rates. The aim of this thesis was to increase the understanding of the coupled hydrological and microbiological processes regulating the denitrification capacity. This was done by applying a broad spectrum of analyses methods, including tracer experiment, water flow modeling, denitrification rate measurements, and analyses of the microbial community structures. The tracer experiment and flow modeling revealed that the wetland design, especially the vegetation, largely can affect the water residence time distributions in wetlands. In the investigated wetland, vegetation dominated the water flow, explaining 60-80% of the variance in water residence times, whereas basin shape only explained about 10% of the variance, but also mixing phenomena significantly affected the residence times and could considerably delay solutes. Measured potential denitrification rates in the wetland exhibited significant spatial variations, and the variations were best described by concentration of nitrogen in sediments and water residence time. Analyses of the denitrifying bacteria populations indicated that a few key populations dominated and that the community diversity increased with decreasing nutrient levels and increasing water residence times. Moreover, it was found that denitrification rates in terms of Menten and first order kinetics can be evaluated by fitting a mathematical expression, considering denitrification and other nitrogen transforming processes to measured product formation in nitrate limited experiments. / QC 20101110

科学研究費補助金 研究種目:基盤研究(B) 課題番号:06554036 研究代表者:吉岡 崇仁 研究期間:1994-1996年度

Thermonuclear fusion may become an attractive future power source. The most promising of all fusion machine concepts is the tokamak. Despite decades of active research, still huge tasks remain before a fusion power plant can go online. One of these important tasks deals with the interaction between the fusion plasma and the reactor wall. This work focuses on how eroded wall materials of different origin and mass are transported in a tokamak device. Element transport can be examined by injection of certain species of unique and predetermined origin, so called tracers. Tracer experiments were conducted at the TEXTOR tokamak before its final shutdown. This offered an unique opportunity for studies of the wall and other internal components: For the first time it was possible to completely dismantle such a machine and analyse every single part of reactor wall, obtaining a detailed pattern of material migration. Main focus of this work is on the high-Z metals tungsten and molybdenum, which were introduced by WF6 and MoF6 injection into the TEXTOR tokamak in several material migration experiments. It is shown that Mo and W migrate in a similar way around the tokamak and that Mo can be used as tracer for W transport. It is further shown how other materials - medium-Z (Ni), low-Z (N-15 and F), fuel species (D) - migrate and get deposited. Finally, the outcome of dust sampling studies is discussed. It is shown that dust appearance and composition depends on origin, formation conditions and that it can originate even from remote systems like the NBI system. Furthermore, metal splashes and droplets have been found, some of them clearly indicating boiling processes. / <p>QC 20151203</p>