Kazuhiro Itoh

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.