Hydrogen Production Using Microorganisms in Hollow-Fiber Bioreactors

For several months, we have continuously operated two types of laboratory-scale, H2-producing bioreactors consisting of semipermeable hollow-fiber bundles inoculated with two metabilically distinct forms of photosynthetic microorganisms. The first employed a hydrogenase activity found in unique strains of photosynthetic bacteria that functions in darkness to shift CO (and H2O) into H2 (and CO2).Mass transport of gaseous CO from thermally gasified biomass into an aqueous bacterial suspension is the rate-limiting step and the main challenge for bioractor design. A simple method using hollow-fiber technology to enhance mass transfer of CO has proven effective. Hydrogen production from CO at an average rate of 125 ml.g cdw-1.h-1 was observed for more than 6 months. In the secondbioreactor, photoproduction of H2 from H2O at an average rate of 9.1 ml.g cdw-1.h-1 was observed in a hollow-fiber photobioreactor incorporating an immobilized Anabaena variabilis mutant that lacked uptake hydrogenase activity. The unique aspect in this case was the use of light energy to produce H2 from water mediated by the cyanobacterium's nitrogenase enzyme complex. The activity lasted for aperiod of 6 months under ambient conditions in the presence of O2.