It is difficult to reuse the construction sludge directly because the water content of it is extremely high. Therefore, it has been disposed as industrial waste in the final disposal site. In order to reduce the construction cost and environmental load, the effective reuse of construction sludge has been an important problem. In order to increase the recycling rate of construction sludge and to solve the above mentioned problem, the authors have already developed a new recycling method for construction sludge by using paper debris and cement. As this method can improve the high water content sludge into high quality ground materials on sites, this method has already been utilized in over 400 construction sites in Japan.

On the other hand, the biodegradation of fibrous materials is not made clear as yet. It is considered qualitatively that fibrous materials used in this method is hard to be biodegraded by soil microbes, because fibrous materials still remains in the soil which was improved by this method 10 years ago. However, the degradation by soil microbes is not confirmed quantitatively.

Therefore, the biodegradability of fibrous materials was investigated experimentally through a culture test and a soil buried test. As a result, it was found that paper fragments were degraded in the solution of pH7.0, but were not degraded in the solution of pH9.5. Furthermore, it was confirmed through soil buried test that paper fragments buried in the normal mud were degraded significantly, but those buried in Fiber-Cement-Stabilized soils were not degraded and fibrous materials remained. Therefore, it was concluded that the fibrous materials in Fiber-Cement-Stabilized soil are not degraded by soil microbes when pH of Fiber-Cement-Stabilized soil is over 9.5, and they remains in the modified soils for a long time.

Recently, the possibility of realizing a subsurface bio-reactor has been realized since microbial methanogenesis has been confirmed in diverse subsurface environments such as coalbeds or petroleum reservoirs. We propose a new gasification method for use in subsurface environments, known as the Subsurface Cultivation and Gasification (SCG). SCG was devised based on the production of biogenic methane gas in subsurface environments. This approach employed hydrogen peroxide to decompose organic matter rapidly. Conversion of organic matter from source rocks into biomethane with the help of microorganisms is expected to be highly profitable. In this study, a series of batch tests using a hydrogen peroxide (H₂O₂) solution were performed on lignite to estimate the potential of low-molecular-weight organic acid production. The effects of several factors on the production of low-molecular-weight organic acids have been considered, such as, concentration of H₂O₂, temperature, liquid-solid ratio, and specific subsurface area of lignite. It was found that the quantity of low-molecular-weight organic acids depended on temperature, liquid-solid ratio, and specific subsurface area of lignite; however, there isn't a unique relationship between them and the H₂O₂ concentration. Moreover, the mass of lignite reduced remarkably when batch tests were performed with a high concentration of H₂O₂. If H₂O₂ is to be injected into a target seam with the SCG method, we should estimate the optimum H₂O₂ concentration to produce low-molecular-weight organic acids with taking into consideration the mechanical stability of the target seam as well as the subsurface environmental chemical reaction with a geological improvement.

A new smelting process of Ti via Bi–Ti liquid alloy is proposed, which comprises reduction of TiCl₄ by Bi–Mg alloy, enrichment of Ti in Bi–Ti alloys, and vacuum distillation of the alloys. In this study, the continuous reduction of TiCl₄ by Bi–Mg alloys and vessel materials for the reduction step were investigated. Firstly, we demonstrated the reduction of TiCl₄ by Bi–Mg alloys and the subsequent recovery of Bi–Ti liquid alloys and MgCl₂ repeatedly. As the result, the alloys containing 5.2–7.4 mol% of Ti were obtained. However, it was found that the reduction rate of TiCl₄ by Bi–Mg alloys is much slower than that by pure Mg because of MgCl₂ layer formed on the alloys, slow mass transfer of Mg in the alloy, and small activity of Mg. For fast reduction of TiCl₄, it is required to inject TiCl₄ into Bi–Mg alloys. Secondly, we kept Bi–10 mol% Ti alloys in stainless steel, soft steel, and Mo crucibles at high temperatures, and measured solubility of each metal in the alloys. The solubility of Mo in the alloy at 900℃ was 220 ppm, and elution from stainless steels and soft steel was dramatically suppressed at 500℃. However, it was found that most Mo in the alloy remains in Bi₉Ti₈ at the segregation cell. To decrease Mo content in Ti product, it is required that the vessel is cooled to lower temperatures than 900℃ or the shorter time of contact between Mo and liquid alloys is desired.