Kazuhiro Itoh

To improve energy production cost, it is necessary to operate bioreactors at a deeper depth to increase per unit area production; however, self-shading could be an inhibiting factor. Therefore, it is important to employ a variety of agitators so that microalgae in deep regions can be agitated, allowing sufficient aeration. We aimed to evaluate the effectiveness of a self-sufficient aerator in an open pond cultivation system for a microalga. Three experimental cases with different agitation velocities (high: Casehigh; low: Caselow; no agitation: Casezero) were evaluated. In Caselow, cells grew fastest in the early stage of cultivation due to reduced mechanical shear stress. However, the increased turbidity after 150 h reduced the cell density and increased chlorophyll a content, which could be attributed to low light intensity. The maximum TAG content was achieved in Casehigh. The findings suggest that strong agitation using an aerator can promote TAG accumulation.

To evaluate biodiesel production from microalgae, a flotation experiment was conducted using the living cell culture fluid of the diatom Chaetoceros gracilis using a venturi tube type microbubble generator. We compared the separation performance of three different culture periods: 1, 2, and 3 weeks from the start of cultivation. After 1 week, the cells were in the logarithmic growth phase, while after 2 and 3 weeks, cell growth had reached the stationary phase. The amounts of triacylglycerol (TAG) in the foam on the surface of the fluid tank were measured. TAG increased during the first 20 min after the start of circulation without additional coagulants and pH adjustment. The disruption of cells was achieved simultaneously. The amounts of TAG in the culture fluids at weeks 2 and 3 were higher than those at week 1. C. gracilis cells in the stationary phase accumulated large amounts of TAG and were easy to disrupt by pressure fluctuation in the venturi tube. These results provide insight into the fracture strength and buoyance of cells for efficiently separating the cells from large volumes of culture fluid.

A new aeration pipe has been developed for wastewater treatment in the food industry.Wastewater from the food industry is perishable due to the occurunce of hydrogen sulfide gas or odor from the deposited sludge near the bottom of the aeration tank. In the present work, we employed the high-speed air injection-type aeration pipe to strengthen the stirring effect. The test aeration pipe was installed near the bottom of the water tank, which is 2m in width and 1.75m in depth of the water. The three-dimensional velocity was evaluated using an electromagnetic velocimeter near the aeration pipe. The three-dimensional circulation flow was observed and the flow rate was evaluated to be about 4 00L/min. The good oxygen transfer efficiency（OTE）was obtained from the measurement of the dissolved oxygen. We have shown examples of wastewater treatment conditions in the implemented plant in the food industry.

We investigate the vapor bubble stability in liquid argon and water using a molecular dynamics simulation. The Lennard-Jones interparticle interaction potential is used to simulate the interaction forces between molecules. The Stillinger' s cluster criterion is employed to classify the vapor molecules evaporated from the bulk liquid. Using this criterion, the vapor molecules are determined to have no neighboring molecules within a 1.23 to 1.32σ radius, where σ is the interaction radius in the L-J potential. The pressure of vapor and liquid phase can be calculated from the virial equation of sate. The stability of bubble is disscussed applying the Young-Laplace equation. The spherical bubble shape is maintained, when the liquid pressure takes the negative value. The thickness of vapor-liquid interface and the number of molecules across vapor-liquid interface are not proportional to the size of bubbles.

In this study, we investigate the vapor bubble stability in liquid argon using a molecular dynamics simulation. The Lennard-Jones (L-J) interparticle interaction potential is used to simulate the interaction forces between argon molecules. The discrimination method based on Stillinger's cluster criterion is employed to classify the vapor molecules evaporated from the bulk liquid. In this criterion, the vapor molecules are determined to have no neighboring molecules within a 1.23 to 1320 sigma radius, where sigma is the interaction radius in the L-J potential. It is found that the spherical bubble shape is maintained and the Young-Laplace equation applies mainly as a result of the large negative pressure of the liquid. The 10-90 thickness of the vapor-liquid interface was approximately 30 to 90% of the bubble radius in the present simulation. A certain frequency of condensation and evaporation was maintained in the smaller bubble case, which is not proportional to the decrease in bubble surface area. (C) 2017 Elsevier B.V. All rights reserved.

The effectiveness of vacuum degassing and steam treatment was examined as a means to reduce waste and increase energy recovery in the treatment of sewage sludge. Equipment using a steam ejector was constructed to apply these treatments consecutively and was able to operate continuously for more than 15 min in an experiment sucking the digestive sludge. The methane component ratio in the bio-gas generated from the treated sludge increased by 11 points. Both the removal of VTS, CODcr and BOD and the digestive efficiency also increased. Further, the use of a water ejector in combination with the steam ejector and reduction of the pressure of degassing was found to promote the solubilization of digestive sludge.