伊藤 和宏

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.

食品加工施設の排水は腐敗しやすく，槽底に滞った汚泥から臭気や硫化水素などが発生し，排水処理施設の能力を低下させる．これに対し，高流速で空気を注入する方式のエアレータを用いて攪拌し，好気性処理を安定させる方法を提案した．地下水槽（幅2m×水深1.75m）の底部にエアレータを設置し，曝気中の流速を3軸電磁流速計で測定した．3次元的な循環流が観察され，循環流量は約400 L/min と推定された．また，溶存酸素量（DO）の測定から，良好な酸素溶解効率（OTE）が得られた．さらに，実際の食品加工排水に適用した場合の処理状況について報告した．

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.

下水廃棄物の減容化とエネルギー回収の向上に対する基礎的検討を目的として，減圧脱気・蒸気処理法を試した．蒸気エジェクタを適用して消化汚泥を連続的に減圧槽に導き，これらの処理を施す装置を試作した．15 min間以上の連続処理が可能であり，処理した汚泥を発酵させた消化ガスのメタン成分が11ポイント増加することを示した．また本処理により，VTS, CODcr, BODの除去率が増加し，消化率も増加することを明らかにした．さらに，水エジェクタと蒸気エジェクタとを組み合わせて，脱気処理時の圧力を下げた実験を行い，可溶化が促進されることを示した