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- 2009 (2) (entfernen)
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- Englisch (2)
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- Chlorine (1)
- Hydrated cement (1)
- LIBS (1)
- Laser-induced breakdown spectroscopy (1)
- Limit of detection (1)
- Methanogenic archaeal community (1)
- Structure and function (1)
- Temperature shift (1)
The microbial community in anoxic rice field soil produces CH4 over a wide temperature range up to 55°C. However, at temperatures higher than about 40°C, the methanogenic path changes from CH4 production by hydrogenotrophic plus acetoclastic methanogenesis to exclusively hydrogenotrophic methanogenesis and simultaneously, the methanogenic community consisting of Methanosarcinaceae, Methanoseataceae, Methanomicrobiales, Methanobacteriales and Rice Cluster I (RC-1) changes to almost complete dominance of RC-1. We studied changes in structure and function of the methanogenic community with temperature to see whether microbial members of the community were lost or their function impaired by exposure to high temperature. We characterized the function of the community by the path of CH4 production measuring δ13C in CH4 and CO2 and calculating the apparent fractionation factor (αapp) and the structure of the community by analysis of the terminal restriction fragment length polymorphism (T-RFLP) of the microbial 16S rRNA genes. Shift of the temperature from 45°C to 35°C resulted in a corresponding shift of function and structure, especially when some 35°C soil was added to the 45°C soil. The bacterial community (T-RFLP patterns), which was much more diverse than the archaeal community, changed in a similar manner upon temperature shift. Incubation of a mixture of 35°C and 50°C pre-incubated methanogenic rice field soil at different temperatures resulted in functionally and structurally well-defined communities. Although function changed from a mixture of acetoclastic and hydrogenotrophic methanogenesis to exclusively hydrogenotrophic methanogenesis over a rather narrow temperature range of 42-46°C, each of these temperatures also resulted in only one characteristic function and structure. Our study showed that temperature conditions defined structure and function of the methanogenic microbial community.
A significant parameter to monitor the status of concrete buildings like bridges or parking garages is the determination of the depth profile of the chlorine concentration below the exposed concrete surface. This information is required to define the needed volume of restoration for a construction. Conventional methods like wet chemical analysis are time- and cost-intensive so an alternative method is developed using laser-induced breakdown spectroscopy (LIBS). The idea is to deploy LIBS to analyze drill cores by scanning the sample surface with laser pulses. Chlorine spectral lines in the infrared (IR) and ultraviolet (UV)-range were studied for chlorine detection in hydrated cement samples. The excitation energies of these spectral lines are above 9.2 eV. Hence high plasma temperatures and pulse energies in the range of some hundred millijoules are needed to induce sufficient line intensity levels at the required working distance. To further increase the line intensity and to lower the detection limit (LOD) of chlorine a measuring chamber is used where different ambient pressures and gases can be chosen for the measurements. The influences on the line intensity for pressures between 5 mbar and 400 mbar using helium as process gas and the influence of different laser burst modi like single and collinear double pulses are investigated. For the first time a LOD according to DIN 32 645 of 0.1 mass% was achieved for chlorine in hydrated cement using the UV line 134.72 nm.