Poster Presentation 2-30
Continuous Hydrogen Photoproduction by Chlamydomonas
reinhardtii
in a Two-stage Chemostat
System
Alexander
S. Fedorov*, Sergey Kosourov,
Michael Seibert and Maria L. Ghirardi
National
Renewable Energy Laboratory
Phone: (303)384-6318
Fax: (303)384-6150
E-mail: alexander_fedorov@nrel.gov
When Chlamydomonas reinhardtii cells are deprived of sulfate,
photosynthetic O2 evolution activity is inhibited substantially, the
culture becomes anaerobic, hydrogenase activity is
induced, and the organism utilizes residual water oxidation activity to produce
hydrogen gas in the light. This process has been studied extensively in C. reinhardtii batch cultures, where the O2-
evolution and H2-production phases are separated temporally in the
same photobioreactor (PhBR).
In the batch system, sulfur deprivation and H2 photoproduction,
lasting 100-150 h, must be followed by a 2-day recovery period after
re-addition of sulfate before H2 photoproduction
can be repeated. This requirement is the result of long-term effects of sulfur
deprivation on other metabolic activities besides O2 evolution. In
order to extend the H2-photoproduction phase, we developed a
two-stage system that separates the O2-evolution and H2-production
phases physically. This system consists of two automated PhBRs,
both operated in chemostat modes. In the first PhBR, the algal culture is grown aerobically under limited
sulfate to obtain photosynthetically competent,
active cells. The cells from the first PhBR are then
fed to the second PhBR, where H2
production occurs continuously under anaerobic conditions. This is the first demonstration
of continuous algal H2 photoproduction for
1500 h, and we have studied the dependence of the H2-production rate
on several growth parameters (e.g., dilution rate, biomass concentration,
incident light intensity). Possible factors limiting H2-photoproduction
rates in the continuous system will be discussed. This work was sponsored by the Hydrogen, Fuel
Cells, and Infrastructure Technologies Program,