Yukio Nakata

Microbial fuel cell (MFC) for bioelectricity generation from organic wastes.

Microbial fuel cells (MFCs) have gained a lot of attention recently as a mode of converting organic matter into electricity. In this study, a compost-based microbial fuel cell that generates bioelectricity by biodegradation of organic matter is developed. Grass cuttings, along with leaf mold, rice bran, oil cake (from mustard plants) and chicken droppings (waste from chickens) were used as organic waste. The electric properties of the MFC under anaerobic fermentation condition were investigated along with the influence of different types of membranes, the mixing of fly ash, and different types of electrode materials. It is observed that the maximum voltage was increased by mixing fly ash. Cellophane showed the highest value of voltage (around 350mV). Bamboo charcoal is good for anode material; however carbon fiber is better for the cathode material in terms of optimization of power generated. This developed MFC is a simple cell to generate electricity from organic waste.

A comparative analysis of the mechanical behavior of carbon dioxide and methane hydrate-bearing sediments

Abstract Understanding the mechanical behaviors of carbon dioxide/methane hydrate-bearing sediments is essential for assessing the feasibility of CO2 displacement recovery methods to produce methane from hydrate reservoirs. In this study, a series of drained triaxial compression tests were conducted on synthetic carbon dioxide hydrate-bearing sediments under various conditions. A comparative analysis was also made between carbon dioxide and methane hydrate-bearing sediments. The stress-strain curves, shear strength, and the effects of hydrate saturation, effective confining stress, and temperature on the mechanical behaviors were investigated. Our experimental results indicate that the newly formed carbon dioxide hydrate would keep the reservoir mechanically stable when CH4-CO2 gas exchange took place in a relatively short period of time and spatially well distributed in the pore space. Experiments of CO2 injection in methane hydrate-bearing sediments are necessary to confirm this hypothesis.

Bonding Strength by Methane Hydrate Formed among Sand Particles

The mechanical properties of methane hydrate‐bearing sand were investigated by low temperature and high confining pressure triaxial testing apparatus in the present study. The specimens were prepared by infiltrating the methane gas into partially saturated sand specimen under the given temperature and stress condition which is compatible with the phase equilibrium condition for the stability of methane hydrate. The tests were firstly performed to investigate the effect of temperature on the shear behaviour of the specimen. Then the effect of backpressure was investigated. The strength of methane hydrate bearing sand increased as the temperature decreased and the back pressure increased. The bonding strength due to methane hydrate was dependent on methane hydrate saturation, temperature and back pressure but independent of effective stress. Dissociation tests of methane hydrate were also performed by applying the temperature to the specimen at the various initial stress conditions. The marked development o...

Influence of Water on the Compression Behavior of Decomposed Granite Soil

In order to investigate the influence of water on compression characteristics of decomposed granite soils, single-particle crushing and one-dimensional compression tests were carried out on three types of decomposed granite soils as well as on quartz-rich silica sand under both dry and wet conditions. Results showed that the initial crushing strength of a single particle was reduced and strength variability increased due to the weakening effects induced by the presence of water. Moreover, it was observed that the one-dimensional compression behavior of decomposed granite soil was related to the initial crushing strength. Finally, the magnitude of initial crushing strength was also affected by the degree of weathering of the soil.

Bioelectricity from kitchen and bamboo waste in a microbial fuel cell

This study evaluated bioelectricity generation by using kitchen garbage (KG) and bamboo waste (BW) as a solid waste management option by a microbial fuel cell (MFC) method. The nutrient content [nitrogen, phosphorus and potassium (NPK)] of the by-products of bioelectricity were also analyzed and assessed for their potential use as a soil amendment. A one-chamber MFC was used for bioelectricity generation in laboratory experiments using both KG and BW. A data-logger recorded voltage every 20 mins at a constant room temperature of 25°C over 45 days. The trend of voltage generation was different for the two organic wastes. In the case of KG, the voltage at the initial stage (0–5 days) increased rapidly and then gradually to a peak of 620 mV. In contrast, the voltage increased gradually to a peak of 540 mV in the case of BW. The by-products of bioelectricity can be used as soil conditioner as its NPK content was in the range of soil conditioner mentioned in other literature. Thus, the MFC has emerged as an efficient and eco-friendly solution for organic waste management, especially in developing and technologically less sophisticated countries, and can provide green and safe electricity from organic waste.

Influence of gravel on the compression characteristics of decomposed granite soil.

Large-scale one-dimensional compression tests were performed in order to analyze the influence of gravel on the compression properties of gravel-mixed decomposed granite soils. After adjusting the gravel contents of the said soil, specimens compacted at a certain level of compaction energy and water content were tested. Based on the test results, it was observed that when gravel-mixed decomposed granite soil was compacted at the same energy level, there existed a specific gravel content at which the dry density was maximum and which also produced the minimum compression index. Furthermore, an expression based on two-phase mixture theory was proposed to quantitatively evaluate the effects of gravel content through a material parameter calculated using the theory, and the estimated compression curves agreed very well with the results of the experiments.

Dynamic Behavior of Granulated Coal Ash during Earthquakes

AbstractCoal ashes discharged from coal-fired power plants have recently been gaining attention as a new form of geomaterials. They have been popularly used as ground materials for the improvement of unsuitable soil and for foam-mixed solidified soil. However, development of more applications is needed in light of the enormous amount of coal ash generated. The current study was performed to confirm the applicability of granulated coal ash (GCA) as reclamation material with adequate resistance against liquefaction during an earthquake. In this study, the liquefaction characteristics of GCA were investigated through cyclic triaxial tests and online pseudodynamic response tests, and the results were compared with those of natural sands to examine the cyclic shear properties of the material. The triaxial test results revealed that the slope of the cyclic shear strength curve of GCA was gentle under high confining pressure, but it was still higher than those of natural sands. It was observed that GCA underwent...

Influence of fines content on the mechanical behavior of methane hydrate-bearing sediments

Methane hydrate-bearing sediments with different amounts of fines content and at three densities were artificially prepared under controlled temperature and pressure conditions. The void ratios of specimens after isotropic consolidation tend to decrease with a rise in fines content. The fines particles enter into the pore space between sand grains and densify the specimens. A series of triaxial compression tests were performed to systematically investigate the influences of fines content and density on the shear properties of hydrate-free sediments and methane hydrate-bearing sediments. The test results demonstrate that a rise in fines content within methane hydrate-bearing sediments significantly enhances peak shear strength and promotes dilation behavior. These influences are particularly prominent for specimens at loose packing state. A decrease in void ratio increases the shear strength and stiffness of hydrate-free sediments and methane hydrate-bearing sediments containing fines content of 0% and 8.9%. It is noted that the formation of methane hydrate in samples with varying amounts of fines content increases the stress ratios at the critical state. The addition of fines particles into coarse-grained sand grains alters the internal microstructure of sand matrix and the hydrate formation pattern in the pore space between sand grains and fines particles.

Green electricity by water plants in organic soil and marine sediment through microbial fuel cell

ABSTRACT In this research, water plants microbial fuel cells (MFCs) were designed for bioelectricity generation. Organic soil and marine sediment were used for fresh water and sea water plants, respectively. It was observed that sea plants were more efficient for bioelectricity generation than the fresh water plants. The peak voltage reached at 520 mV when Phragmites australis was used. The MFCs without plants always showed significantly lower (80% lower) voltage in both soils. Seasonal variation was not prominent; however, daily solar radiation had noteworthy influences on voltage generation for both plants.

TWO SURFACE MODEL FOR SOILS WITH INDUCED ANISOTROPY

In order to evaluate the stress-strain behaviour of anisotropically consolidated and over-consolidated soils in a limited stress region, an elasto-plastic constitutive model, taking account of anisotropy effects induced by the initial consolidation, were developed based on the bounding suface plasticity. The model proposed consists of a set of bounding surface, loading surface, plastic potential and hardening modulus. The model contains nin experimental parameters which are easily determined from a few conventional triaxial tests. It was shown that the model was able to reasonably represents the stress-dilatancy properties of over-consolidated sand.