Continuous Hydrogen Photoproduction by Chlamydomonas reinhardtii: Using a novel two-stage, sulfate-limited chemostat system

This study demonstrates, for the first time, that it is possible to couple sulfate-limited Chlamydomonas reinhardtii growth to continuous H₂ photoproduction for more than 4000 h. A two-stage chemostat system physically separates photosynthetic growth from H₂ production, and it incorporates two automated photobioreactors (PhBRs). In the first PhBR, the algal cultures are grown aerobically in chemostat mode under limited sulfate to obtain photosynthetically competent cells. Active cells are then continuously delivered to the second PhBR, where H₂ production occurs under anaerobic conditions. The dependence of the H₂ production rate on sulfate concentration in the medium, dilution rates in the PhBRs, and incident light intensity is reported.