報告書番号

U98051

タイトル（和文）

微生物によるCO2固定 8. -連結した螺旋状チューブラーリアクターにおける培養液の流れの諸条件とクロレラの光合成生産-

タイトル（英文）

Microbial CO2 fixation 8. Conditions of medium flow and photosynthetic production of Chlorella in combined unit system of cone-shaped helical tubular photobioreactors

概要 （図表や脚注は「報告書全文」に掲載しております）

実用化を想定できるシステムを示すため、効率の良い基本ユニットを多数連結化する方法を検討した。培養液流速を一定に保った条件で通気速度のみを変化させた場合、通気速度の増加に伴いクロレラの生産性が上がり、ピークに達した後低下した。これはCO２供給のプラス効果と、培養液の撹拌が過剰になることにより生じる細胞へのマイナス影響のバランスによっておこる現象と考えられ、含CO２ガス流量を適切に保つ必要性が示された。次に、当所提案の螺旋状チューブラーリアクターについて、培養液の流れの状態に着目し、培養液の流速と生産性の関係について、理論的かつ実験的に検討を行った。これにより、１ユニットと同じ培養液の流れの状態を２及び４ユニット連結のシステムで再現することができ、流れの状態を保った場合に生産性の維持が可能であった。以上の検討により、１ユニットの現象を再現できる、ユニットの連結化を図ることが可能となった。

概要 （英文）

We have been investigating the microalgal CO2 fixation / conversion technology in order to contribute to the mitigation of global warming. We have proposed a cone-shaped helical tubular photobioreactor (HTP) and indicated an advantage of the HTP in view of photosynthetic efficiency. Also, the appropriate HTP design of the basic unit was decided. It was difficult to keep a high photosynthetic productivity in a large-sized system as a medium fluidity was different from that in a basic system. Therefore it is necessary to establish a combined unit system so as to increase CO2 fixation mass instead of the large-sized system. In this report, we investigated a relationship between the medium fluidity and photosynthetic productivity of Chlorella biomass under an air-lift operation and examined a combined unit system of the HTPs. Firstly, the culture apparatus capable of keeping a medium flow rate steady and adjusting an air flow rate was utilized to clarify the effect of the air flow rate on a photosynthetic productivity. The productivity increased first, reached a peak at the air flow rate of 1.0 L/min and then decreased as the air flow rate increased in a constant medium flow rate (0.98 L/min). This seemed to be due to a balance between a positive effect of CO2 supply by increasing the air flow rate and a negative effect to microalgae by an excessive agitation of medium. This result shows the importance of keeping the air flow rate reasonable under the air-lift operation. Secondly, the medium flow rate was calculated theoretically using two-phase gas-liquid flow equations and adjusted by changing heights of the HTP parts in order to clarify the relationship between the medium flow rate and photosynthetic productivity under the air-lift operation, and the productivity was examined. The order of medium fluidity calculated theoretically was same as that measured experimentally. The HTP which had high medium fluidity attained higher productivity. Photosynthetic productivity increased with an increase of the medium flow rate under the medium flow rate of 0.95 L/min. Lastly, we examined the combined unit system of two or four HTP units so as to reproduce the condition of one unit. The medium fluidity at two or four HTP units was same as that of one unit as predicted theoretically. The photosynthetic productivity per the HTP at two or four HTP units was same or a little higher than that at one unit by keeping the same medium fluidity as one unit. From these results, an appropriate combined unit system was successfully established, which means the increase of CO2 fixation mass.

報告者

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