Crynodeb
Low enthalpy geothermal heat – using open-loop ground source technology to recover and store heat from abandoned flooded coal mines – is an important aspect of decarbonising heating and energy systems. In this thesis, the biogeochemistry of coal mine groundwater was investigated, with the aim of understanding the relevant relationship between microbial activities and low-carbon energy technologies. Organic matter leaching from coal under short-time controlled laboratory experiments demonstrated that different bioavailable molecules can be formed due to hydroxyl radical formation, especially in oxygenated conditions. Furthermore, long-term experiments, monitored through microcalorimetry, under strictly anoxic conditions and using a microbial inoculum, demonstrated that coal could sustain microorganism activity under strictly oligotrophic conditions. These findings imply that coal carbonaceous material, widely considered recalcitrant, could be relevant in the carbon cycle in coal mine groundwater and that the activity of microorganisms towards coal degradation results in energy dissipation in form of heat. In situ investigations using a multi-isotopic and techniques developed and applied for metabolomic analyses (FI-ESI-MS) together with traditional geochemical techniques have revealed the presence of a cryptic sulfur cycle in coal mine groundwaters, potentially widespread also in other subsurface environments. Sulfate reduction and methanogenesis are key biogeochemical processes in coal mine groundwater, wherein hydrogen sulfide re-oxidation masks the microbial sulfate -reducing activity.Sequencing of 16S rDNA genes from the biofilm formed on incubated material in coal mine water, suggests that this community structure contains metabolic capacity for both oxidative and reductive sulfur transformations, which are relevant in relation to biofouling and corrosion of geothermal heat recovery installations, and the long-term viability of such schemes. Specifically, the control of f H2S concentrations is related to the presence of microorganisms capable of oxidizing hydrogen sulfide to sulfate. In this regard, mineral phases – such as pyrite and elemental sulfur – that are not considered important in the context of coal mine waters and biofouling, have become an essential component in the
mineral phases dominating the scaling in presence of trace amount of H2S. This work has furthered our understanding of subsurface coal based biogeochemical cycles and enhanced critical knowledge required for the long-term implementation of low-carbon energy technologies.
| Dyddiad Dyfarnu | 2024 |
|---|---|
| Iaith wreiddiol | Saesneg |
| Sefydliad Dyfarnu |
|
| Goruchwyliwr | Andrew P. Mitchell (Goruchwylydd), Gareth Farr (Goruchwylydd) & Arwyn Edwards (Goruchwylydd) |