Phase 4 identified two specific targets for study:
(1) Research related to biomethanation of organic matter found in geological formations: evaluation of methods related to biologic processes to release methane harbored in siliceous rocks and lignite formations, and the storage ability, subterranean transfer characteristics, and relevant parameters for the development of an in situ model.
(2) Research related to underground fixation of CO2: isolation of organisms that can be utilized for the biological fixation of CO2, and improved understanding of the void structures and geochemical characteristics of siliceous and lignite formations in which CO2 storage occurs.
To achieve these objectives, the Subsurface Microbiology Research Group, Groundwater Environment Research Group, and Sedimentary Rock Research Group each established a number of research tasks, addressing inquiries in several fields ranging from field science to basic technology development. Since past research results were expected to contribute to research into methanogenesis within geological formations, in FY 2013, we decided to conduct research focusing on this topic; this research is described further below.
　The Subsurface Microbiology Research Group conducted research related to seeking and evaluating methanogenic microorganisms and microorganisms that produce methanogenic substrates, in addition to studies of subsurface microbial community structure and CO2-fixing microbes. In FY 2013, the Group plans to collect Wakkanai Formation rocks and groundwater from a 350-meter tunnel in the JAEA underground facility, as well from unweathered lignite from a 200-meter deep underground exploratory drilling site in the Sarufutsu mining area of the Tempoku coalfields, and is considering research utilizing these samples. The Group also attempted to clarify the properties of new methanogenic microorganisms that were the most predominant in the deep subsurface in Horonobe, and carried out the study on the decomposition of refractory organic matter in sedimentary rock as an initial process in the methanation of unused organic matter in the sedimentary rocks, as well as research on the structural changes due to microorganisms. In collaboration with the Groundwater Environment Research Group, the Subsurface Microbiology Research Group also studied the decomposition of persistent organic matter in sedimentary rocks using diluted hydrogen peroxide.
　The Groundwater Environment Research Group identified the mechanism by which substrates for methanogenic microorganisms are formed and conducted geochemical research related to geological storage of CO2. To clarify the origin of dissolved methane in the Quaternary and Tertiary formations around Horonobe, the Groundwater Environment Research Group carried out geochemical analysis on samples obtained in the above-mentioned formations. Moreover, using analysis equipment introduced in FY2013, the Group quantified the hydrogen concentration in groundwater while also analyzing its relationship to the metabolic activity of methanogenic microorganisms. The Group also analyzed the composition of humic substances contained in a variety of sedimentary rocks, including lignite, assessing the effects of weathering and hydrothermal alterations on the composition of the organic matter found in these rocks. As part of ongoing research to develop means of converting the organic matter in geological formations to low-molecular-weight organic acids that can be used by methanogenic microorganisms, the Group studied the oxidation (decomposition) of organic matter in sedimentary rocks by hydrogen peroxide, dissolved oxygen, and similar agents. The Group also conducted research related to organic matter elution by chelating agents and the relationship between calcite supersaturation and methanogenesis pathways as basic research related to CO2 fixation in geologic formations.
　Since rock mechanics and geotechnical engineering are important in realizing biomethane recovery and CO2 fixation, the Sedimentary Rock Research Group investigated the pore characteristics of sedimentary rock, conducting research related to the effects that failure and deformation of rock have on osmosis in sedimentary rock. This research evaluated the pore properties of lignite using a micro-focus X-ray CT scanner, which revealed changes in internal structures that developed during the saturation and drying process. The Sedimentary Rock Research Group also analyzed the constituent elements of samples, using an electron probe microanalyzer and fluorescent X-ray analysis. Using lignite specimens collected during drilling surveys of the Sarufutsu mining area of the Tempoku coalfields, the Group also investigated a variety of physical characteristics and strength and deformation properties.