報告書番号

V12006

タイトル（和文）

微生物によるBDF副生グリセロール廃液からのエタノール生産

タイトル（英文）

Microbial conversion of crude glycerol generated from biodiesel fuel production into ethanol

概要 （図表や脚注は「報告書全文」に掲載しております）

当所が有するエタノール生産微生物について、バイオディーゼル燃料（BDF）を生産する際に副生するアルカリ性のグリセロール廃液からのエタノール生産性を調査し、連続的培養の最適化を図った。当所が有する2種類のエタノール生産微生物（NS-1株、NS-3株）についてグリセロール純品を含有させアルカリ環境で培養試験を実施した結果、エタノール変換効率（エタノール生成量/グリセロール消費量）はpHの影響を受けず、NS-1株では92.7%という高い変換効率を維持した。さらに、pH未調整のグリセロール廃液含有培養液（pH=9）からもエタノールの生成が確認された（エタノール変換効率72.5%）。アルカリ環境下でグリセロールからのエタノール生産を始めて実証した。
NS-1株によるエタノール連続生産培養のシミュレーションを実施した。現状の最高値（28.1g/L）に匹敵する約600mM（27.6g/L）のエタノールを定常的に生産可能と予測された。

概要 （英文）

Glycerol is produced as a byproduct in biodiesel fuel (BDF) production. Generally, glycerol is produced at concentrations of 10% the amount of BDF produced, which can then be converted into useful chemicals by microbial fermentation. We previously isolated two species of bacteria that could convert glycerol to ethanol. However, the ability of these bacteria to produce ethanol from crude glycerol was unknown. Crude glycerol has high alkalinity due to the introduction of an alkaline catalyst during BDF production. In this study, we investigated the conversion activity against crude glycerol, and numerically simulated the performance of ethanol production under continuous cultivation.
Two bacterial strains—NS-1 and NS-3—originally obtained from our institute, were used in this study. First, we investigated their ethanol-producing activity from pure glycerol under high pH conditions (up to pH = 9). The ethanol-producing activity was not affected by pH. In addition, the ethanol conversion ratio (ethanol production/glycerol consumption) was maintained from pH 7 to 9 at approximately 90% and 40% for NS-1 and NS-3 strains, respectively. Next, the ethanol-producing activity of the NS-1 strain was investigated against a medium containing crude glycerol with a pH of 9. Ethanol production was observed and almost all of the glycerol was consumed within 7 days, with an ethanol conversion ratio of 72.5%. This is the first study, to the best of our knowledge, to demonstrate the bioconversion of crude glycerol to ethanol under alkaline conditions.
A numerical growth simulation for continuous cultivation of ethanol production from crude glycerol was performed using the NS-1 strain. In this simulation, the initial glycerol concentration was assumed to be 50 mM, and maintained at this level while crude glycerol was periodically added. Consequently, the ethanol concentration reached a final level of 600 mM, which is the highest concentration level reported to date.

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