Continuous hydrogen production during fermentation of α-cellulose by the thermophillic bacterium Clostridium thermocellum
✍ Scribed by Lauren Magnusson; Nazim Cicek; Richard Sparling; David Levin
- Publisher
- John Wiley and Sons
- Year
- 2009
- Tongue
- English
- Weight
- 190 KB
- Volume
- 102
- Category
- Article
- ISSN
- 0006-3592
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✦ Synopsis
Abstract
Continuous hydrogen (H~2~) production during fermentation of α‐cellulose was established using the thermophillic, anaerobic bacterium Clostridium thermocellum ATCC 27405. The objectives of this work were to characterize growth of C. thermocellum, quantify H~2~ production and determine soluble end‐product synthesis patterns during fermentation of a cellulosic substrate under continuous culture conditions. A 5 L working volume fermentor was established and growth experiments were maintained for over 3,000 h. Substrate concentrations were varied from 1 to 4 g/L and the feed was introduced with continuous nitrogen gas sparging to prevent clogging of the feed‐line. The pH and temperature of the reactor were maintained at 7.0 and 600°C, respectively, throughout the study. At concentrations above 4 g/L, the delivery of α‐cellulose was impaired due to feed‐line clogging and it became difficult to maintain a homogenous suspension. The highest total gas (H~2~ plus CO~2~) production rate, 56.6 mL L^−1^ h^−1^, was observed at a dilution rate of 0.042 h^−1^ and substrate concentration of 4 g/L. Under these conditions, the H~2~ production rate was 5.06 mmol h^−1^. Acetate and ethanol were the major soluble end‐products, while lactate and formate were greatly reduced compared to production in batch cultures. Concentrations of all metabolites increased with increasing substrate concentration, with the exception of lactate. Despite a number of short‐term electrical and mechanical failures during the testing period, the system recovered quickly, exhibiting substantial robustness. A carbon balance was completed to ensure that all end‐products were accounted for, with final results indicating near 100% carbon recovery. This study shows that long‐term, stable H~2~ production can be achieved during direct fermentation of an insoluble cellulosic substrate under continuous culture conditions. Biotechnol. Bioeng. 2009; 102: 759–766. © 2008 Wiley Periodicals, Inc.