Methane (CH4) plays an important role in regulating Earth’s climate. Its atmospheric concentrations are related to both biotic and abiotic processes. The biotic one can be formed either by chemoautotrophic or heterotrophic pathways by methanogens. Abiotic CH4 formation can occur from several sequential reactions starting with H2 production by serpentinization of Fe-bearing minerals followed by Fischer-Tropsch Type reactions or thermogenic reactions from hydrocarbons. In the presence of suitable electron acceptors, microbial oxidation utilizes CH4 and contributes to regulating its emission.  From the perspectives of astrobiology and Earth climate regulation, this thesis focuses on: (1) Dynamics of CH4 formation and oxidation in lake sediments (Paper I), (2) Constructing an automatic flux chamber to facilitate its emission measurements (Paper II), (3) dynamics of both abiotic and biotic CH4 formation processes related to olivine water interaction in temperature range 30 - 70°C (Paper III and IV). Paper I showed that potential CH4 oxidation strongly correlated to in situ its formation rates across a wide variety of lake sediments. This means that the oxidation rates could be enhanced in environments having the high formation rates. Thereby, the oxidation would likely be able to keep up with potentially increasing the formation rates, as a result diffusive CH4 release from freshwater sediments might not necessarily increase due to global warming. Paper II presented a new automated approach to assess temporal variability of its aquatic fluxes. Paper III and IV together revealed that H2 can be formed via olivine-water interaction. Abiotic CH4 formation was formed likely by Fischer-Tropsch Type reactions at low inorganic carbon concentration but by thermogenic processes at high inorganic carbon concentration. Paper IV showed that biotic methanogenic metabolism could harvest H2 and produce CH4. The dynamics of these processes seemed strongly affected by carbonate chemistry. / At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Manuscript. Paper 4: Submitted.

The aim of this thesis was to determine effect of drainage, restoration and addition of mineral and organic nitrogen to spruce swamp forest soil on potential methane production and oxidation. Six study sites (2 pristine, 2 drained and 2 restored) were located in Šumava National Park in the Czech Republic.

Methane derived authigenic carbonate (MDAC) precipitation occurs within marine sediments as a byproduct of the microbial anaerobic oxidation of methane (AOM). While these carbonates form in chemical and isotopic equilibrium with the fluids from which they precipitate, burial diagenesis and recrystallization can overprint these signals. Plane polarized light (PPL) and cathodoluminescent (CL) petrography have allowed for detailed characterization of carbonate phases and their subsequent alteration. Modern MDACs sampled offshore in northern Cascadia (n =33) are compared with paleoseep carbonates (n =13) uplifted on the Olympic Peninsula in order to elucidate primary vs. secondary signals, with relevance to interpretations of the carbonate record. The modern offshore environment (S. Hydrate Ridge and Barkley Canyon) is dominated by metastable acicular and microcrystalline aragonite and hi-Mg calcite (HMC) that with time will recrystallize to low-Mg calcite (LMC). The diagenetic progression is accompanied by a decrease in Mg/Ca and Sr/Ca ratios while variation in Ba/Ca depends upon the Ba-concentration of fluids that spur recrystallization. CL images discern primary carbonates with high Mn/Ca from secondary phases that reflect the Mn- enrichment that characterizes deep sourced fluids venting at Barkley Canyon. Methane along the Cascadia continental margin is mainly of biogenic origin, where reported strontium isotopic values reflect a mixture of seawater with fluids modified by reactions with the incoming Juan de Fuca plate. In contrast, the Sr-isotopic composition of carbonates and fluids from Integrated Ocean Drilling Program (IODP) Site U1329 and nearby Barkley Canyon point to a distinct endmember (lowest ⁸⁷Sr/⁸⁶Sr = 0.70539). These carbonates also show elevated Mn/Ca and δ¹⁸O values as low as -12‰, consistent with a deep-source of fluids feeding thermogenic hydrocarbons to the Barkley Canyon seeps. Two paleoseep carbonates sampled from the uplifted Pysht/Sooke Fm. have ⁸⁷Sr/⁸⁶Sr values similar to those of the anomalous Site U1329 and Barkley Canyon carbonates (⁸⁷Sr/⁸⁶Sr = 0.70494 and 0.70511). We postulate that the ⁸⁷Sr-depleted carbonates and pore fluids found at Barkley Canyon represent migration by the same type of deep, exotic fluid as is found in high permeability conglomerate layers down to 190 mbsf at Site U1329, and which fed paleoseeps in the Pysht/Sooke Fm. These exotic fluids likely reflect interaction with the 52-57 Ma igneous Crescent Terrane, which is located down-dip from both Barkley Canyon and Site U1329. This previously unidentified endmember fluid in northern Cascadia may have sourced cold seeps in this margin since at least the late Oligocene. / Graduation date: 2012

Doctor of Philosophy (PhD) / Ultra-lean methane combustion in porous burners is investigated by means of a pilot-scale demonstration of the technology supported by a computational fluid dynamics (CFD) modelling study. The suitability of porous burners as a lean-burn technology for the mitigation of methane emissions is also evaluated. Methane constitutes 14.3% of total global anthropogenic greenhouse gas emissions. The mitigation of these emissions could have a significant near-term effect on slowing global warming, and recovering and burning the methane would allow a wasted energy resource to be exploited. The typically low and fluctuating energy content of the emission streams makes combustion difficult; however porous burners—an advanced combustion technology capable of burning low-calorific value fuels below the conventional flammability limit—are a possible mitigation solution. A pilot-scale porous burner is designed expressly for the purpose of ultra-lean methane combustion. The burner comprises a cylindrical combustion chamber filled with a porous bed of alumina saddles, combined with an arrangement of heat exchanger tubes for preheating the incoming methane/air mixture. A CFD model is developed to aid in the design process. Results illustrating the operating range and behaviour of the burner are presented. Running on natural gas, the stable lean flammability limit of the system is 2.3 vol%, a considerable extension of the conventional lean limit of 4.3 vol%; operating in the transient combustion regime allows the lean limit to be reduced further still, to 1.1 vol%. The heat exchanger arrangement is found to be effective; preheat temperatures of up to 800K are recorded. Emissions of carbon monoxide and unburned hydrocarbons are negligible. The process appears stable to fluctuations in fuel concentration and flow rate, typically taking several hours to react to any changes. A CFD model of the porous burner is developed based on the commercial CFD code ANSYS CFX 12.0. The burner is modelled as a single 1-dimensional porous domain. Pressure loss due to the presence of the porous solid is accounted for using an isotropic loss model. Separate energy equations for the gas and solid phases are applied. Models for conductive heat transfer within the solid phase, and for convective heat transport between the gas and solid phases, are added. Combustion is modelled using a finite rate chemistry model; a skeletal mechanism for ultra-lean methane combustion is developed and incorporated into the model to describe the combustion reaction. Results from the model are presented and validated against experimental data; the model correctly predicts the main features of burner behaviour. Porous burners are found to show potential as a methane mitigation technology.

Doctor of Philosophy (PhD) / Ultra-lean methane combustion in porous burners is investigated by means of a pilot-scale demonstration of the technology supported by a computational fluid dynamics (CFD) modelling study. The suitability of porous burners as a lean-burn technology for the mitigation of methane emissions is also evaluated. Methane constitutes 14.3% of total global anthropogenic greenhouse gas emissions. The mitigation of these emissions could have a significant near-term effect on slowing global warming, and recovering and burning the methane would allow a wasted energy resource to be exploited. The typically low and fluctuating energy content of the emission streams makes combustion difficult; however porous burners—an advanced combustion technology capable of burning low-calorific value fuels below the conventional flammability limit—are a possible mitigation solution. A pilot-scale porous burner is designed expressly for the purpose of ultra-lean methane combustion. The burner comprises a cylindrical combustion chamber filled with a porous bed of alumina saddles, combined with an arrangement of heat exchanger tubes for preheating the incoming methane/air mixture. A CFD model is developed to aid in the design process. Results illustrating the operating range and behaviour of the burner are presented. Running on natural gas, the stable lean flammability limit of the system is 2.3 vol%, a considerable extension of the conventional lean limit of 4.3 vol%; operating in the transient combustion regime allows the lean limit to be reduced further still, to 1.1 vol%. The heat exchanger arrangement is found to be effective; preheat temperatures of up to 800K are recorded. Emissions of carbon monoxide and unburned hydrocarbons are negligible. The process appears stable to fluctuations in fuel concentration and flow rate, typically taking several hours to react to any changes. A CFD model of the porous burner is developed based on the commercial CFD code ANSYS CFX 12.0. The burner is modelled as a single 1-dimensional porous domain. Pressure loss due to the presence of the porous solid is accounted for using an isotropic loss model. Separate energy equations for the gas and solid phases are applied. Models for conductive heat transfer within the solid phase, and for convective heat transport between the gas and solid phases, are added. Combustion is modelled using a finite rate chemistry model; a skeletal mechanism for ultra-lean methane combustion is developed and incorporated into the model to describe the combustion reaction. Results from the model are presented and validated against experimental data; the model correctly predicts the main features of burner behaviour. Porous burners are found to show potential as a methane mitigation technology.

No description available.

Call number: LD2668 .T4 1984 N43 / Master of Science

The availability of substrates is one of the most important environmental constraints on the diversity and functioning of microorganisms. Substrate quantity and quality as well as the metabolic features of heterotrophic microorganisms determine the efficiency, speed and type of transformation that can occur in nature. As such their interplay with the environment regulates how much carbon and energy is incorporated by bacteria and subsequently reaches higher trophic levels. In lakes the bulk substrate that is available for bacteria is composed of a complex mixture of compounds, varying in lability and distribution in the environment. This thesis addresses the coupling of organic substrates, their metabolic use and the composition and ecology of the microbial community. Controlled laboratory experiments with mixed bacterial communities in either batch cultures or chemostats were designed to shed further light on bacterial use of labile and quantitatively significant carbon compounds. I show that different amino acid substrates only exert a minor influence on bacterioplankton community composition and growth. Hence the ability to use a wide range of such abundantly produced protein monomers seems to be widespread among freshwater bacteria. In contrast, when acetate was provided as the only carbon substrate, in either pulsed or continuous amendments, this very different substrate input mode had a strong effect on bacterial community composition. Biomass yield, for example, was twice as high when acetate was given in the form of pulses rather than provided continuously. In another set of experiments, I show that the oxidation of the globally significant greenhouse gas methane is a process that can potentially take place at the water-ice interface of seasonally ice-covered lakes and was not constrained by temperature as suggested in previous studies. This work also suggests that methane oxidation in ice-covered lakes can be constrained by competition for nutrients between specialized methanotrophs and heterotrophic bacteria. Combined these studies suggest that some labile substrates cause minor selection on bacterial community structure and functioning. This probably reflects the competitive advantage of using a broad range of low molecular weight substrates. However, as in the case of methanotrophs there is specialization for a specific low molecular weight substrate such as methane. In which case, competition with other community members i.e. for nutrients can constrain methane oxidation. In both cases it might however not depend just on the availability of substrate, but also on how substrates are distributed in time and space.

Fuel processing is one of the essential parts for development of intermediate solid oxide fuel cells (IT-SOFC). Natural gas (methane) is considered as the most abundant and cost effective fuel for the production of hydrogen for IT-SOFC. The primary aim of this thesis is to use a novel precursor material—layered double hydroxide (LDH) – for developing a new type of cost effective, highly active and long lasting catalyst which can reform natural gas in IT-SOFC anode environment. Small amount of noble metals Pd, Rh and Pt are used as promoters to enhance the catalyst’s performance as while maintaining the cost relatively low. The research objectives are achieved by a series of studies including catalysts synthesis, characterisation and the catalytic activities. The thesis initially gives a comprehensive review on fuel cell and SOFC technology, steam methane reforming and reforming catalyst to provide better understanding of the research. Experimental studies include the effects of the synthetic conditions of the LDH precursors and thermal treatments on the physical, chemical behaviours and catalytic activities of the catalysts and promotional effects by noble metals. The LDH derived catalysts compositions, promoter quantities and operating conditions are optimised for the best performance in the IT-SOFC anode environment. A new method for the development of precursor sol for easy coating of the anode is developed and studied. The sol preparation is achieved by acid attack. The sol developed is found to produce better coating and has very high catalytic properties after activation. The catalysts developed were tested for their stability and self-activation ability to ensure its use in the commercial cells. The findings of the present study indicate that the catalysts developed show excellent catalytic performance and these catalysts have very high potential for further commercialisation in IT-SOFC.

No description available.