In FY 2016, the Subsurface Microbiology Research Group, Groundwater Environment Research Group, and Sedimentary Rock Research Group each proposed and conducted research on several projects in field science and development of basic technology concerning biomethane generation in geological formations, described further below.
　The Subsurface Microbiology Research Group continued its investigation of the microbial community structure of the diatomaceous mudstone formations of the JAEA’s Horonobe URL, while also attempting to analyze the microbial community structure in groundwater of lignite formations in the Sarufutsu mining area of the Tempoku coalfields. The Group overcame problems with the water sampling equipment installed the previous year, improving these devices and developing a new water sampling system, making groundwater sampling under anaerobic conditions possible. Using the improved water sampling equipment, the Group found that, by minimizing exposure of groundwater samples to oxygen during sampling, it was possible to collect groundwater under close-to-in situ conditions. The Group made improvements in cultivation models to reflect in situ temperatures, for better research on methanogenic processes in geological formations, and found that, as the culture temperature decreased, the methanogenesis volume and rate also tended to decrease, and that differences in microbial community structures arose owing to changes in culture temperature. The Group also found that the selection of the solid phase added to the culture solution and affecting methanogenesis is important for developing an in situ test model. As part of its analysis of intermediate metabolites of methane source materials, the Group showed that, under anaerobic conditions, microorganisms decomposed monocyclic aromatic moieties of humic substances, which was revealed by pyrolysis–GC/MS analysis.
　The Groundwater Environment Research Group analyzed carbon isotope ratios from methane dissolved in groundwater of the Sarufutsu mining area of the Tempoku coalfields, and found that the methane in this area was of microbial origin introduced via meteoric water recharge. The Group measured the carbon and oxygen isotope ratios of carbonate minerals associated with the Cretaceous formations and the upper part of coal formations of northern Hokkaido. It is suspected that the activity of methanogens in coal formations increased as part of the process of the coal formation, rising to shallow surface areas where the temperature is less than 70 ℃. The Group conducted indoor experiments using hydroquinone, during the study of the hydrogen generation mechanism in the subsurface, and found that hydrogen production volume depends on pH.
　Analyses of water sampled from an existing hot spring well in northern Hokkaido revealed that high concentrations of iodine and dissolved methane coexist, and that this methane originates from both microbes and the thermal decomposition of organic matter. As part of basic technology development, the Group investigated the pH dependence of the reaction between lignite and hydrogen peroxide, and found a tendency for the amount of organic acid produced from lignite to decrease with increasing pH. They also examined the reactivity of lignite, subbituminous coal, and bituminous coal to hydrogen peroxide, and found that the lower the thermal maturity of the coal is, the higher the reaction rate with hydrogen peroxide is.
　The Sedimentary Rock Research Group conducted various physical, chemical, and mechanical tests on lignite in order to describe the characteristics of sedimentary rock during biomethane production. In particular, to evaluate the physical and mechanical properties of lignite, the Group used lignite samples from rocky outcrops and boring cores to measure elastic wave velocity using the ultrasonic pulse method and conduct unconfined compression tests, to conduct elemental analyses via non-destructive X-ray fluorescence analysis, and to measure permeability through one-dimensional permeability testing. Visual measurements of lignite structures were carried out using a micro-focus X-ray CT scanner to evaluate special mechanical characteristics. The Group also studied the effects of anisotropy, based, in large part, on the direction of cleat in lignite. Considering the promotion of the decomposition of organic matter by hydrogen peroxide, the Group also considered the mechanical properties of lignite during the decomposition of organic matter. In order to obtain design materials for in situ testing of methods for biomethane production technology in sedimentary rock formations, the Group simulated the in situ deposition environment, encouraging the decomposition of organic matter in sedimentary rock by means of hydrogen peroxide and thus evaluating changes in the chemical properties of solvents over time as well as changes to the properties of sedimentary rock.