Microbial hydrogen production
- National Renewable Energy Lab., Golden, CO (United States); and others
Photosynthetic bacteria inhabit an anaerobic or microaerophilic world where H{sub 2} is produced and consumed as a shared intermediary metabolite. Within a given bacterial isolate there are as many as 4 to 6 distinct enzymes that function to evolve or consume H{sub 2}. Three of the H{sub 2}-evolving physiologies involving three different enzymes from photosynthetic bacteria have been examined in detail for commercial viability. Nitrogenase-mediated H{sub 2} production completely dissimilates many soluble organic compounds to H{sub 2} and CO{sub 2} at rates up to 131 {mu}mol H{sub 2}{sm_bullet}min{sup -1}{sm_bullet}g cdw{sup -1} and can remain active for up to 20 days. This metabolism is very energy intensive, however, which limits solar conversion efficiencies. Fermentative hydrogenase can produce H{sub 2} at rates of 440 {mu}mol{sm_bullet}min{sup -1}{sm_bullet}g cdw{sup -1} at low levels of irradiation over indefinite periods. The equilibrium for this activity is low (<0.15 atmospheres), thereby requiring gas sparging, vacuuming, or microbial scavenging to retain prolonged activity. Microbial H{sub 2} production from the CO component of synthesis or producer gases maximally reaches activities of 1.5 mmol{sm_bullet}min{sup -1}{sm_bullet}g cdw{sup -1}. Mass transport of gaseous CO into an aqueous bacterial suspension is the rate-limiting step. Increased gas pressure strongly accelerates these rates. Immobilized bacteria on solid supports at ambient pressures also show enhanced shift activity when the bulk water is drained away. Scaled-up bioreactors with 100-200 cc bed volume have been constructed and tested. The near-term goal of this portion of the project is to engineer and economically evaluate a prototype system for the biological production of H{sub 2} from biomass. The CO shift enables a positive selection technique for O{sub 2}-resistant, H{sub 2}-evolving bacterial enzymes from nature.
- Research Organization:
- National Renewable Energy Lab. (NREL), Golden, CO (United States)
- OSTI ID:
- 183300
- Report Number(s):
- NREL/CP-430-20036-Vol.2; CONF-9504160-VOL.2; ON: DE95009296; TRN: 95:008711-0012
- Resource Relation:
- Conference: 1995 DOE/NREL hydrogen program review, Coral Gables, FL (United States), 18-21 Apr 1995; Other Information: PBD: Sep 1995; Related Information: Is Part Of Proceedings of the 1995 US DOE hydrogen program review, Volume II; PB: 876 p.
- Country of Publication:
- United States
- Language:
- English
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