Hydrogen Production by Sulfur-Deprived Chlamydomonas reinhardtii Under Photoautotrophic Conditions

Thus far, all experiments leading to H₂ production by sulfur-deprived cultures of microalga have been done with photoheterotrophic cultures in the presence of acetate, which increases the cost of the H₂ produced. This study demonstrates that sustained H₂ photoproduction by a sulfur-deprived green alga, Chlamydomonas reinhardtii, is possible under strictly photoautotrophic conditions in the absence of acetate or any other organic substrate in the medium. To accomplish this, we used cultures pre-grown with 2% CO₂ under low light conditions (25 μ E m^{- 2} s^{- 1}) and also supplemented with CO₂ during S-deprivation along with a special light regime. Maximum H₂ production (56.4 ± 16.7 ml l^{- 1} culture, equal to 56.4 × 10^{- 3} m³ m^{- 3} culture) was observed with photoautotrophic cultures: (a) supplied with carbon dioxide for the first 24 h of sulfur deprivation, (b) exposed during the O₂-producing stage to high light (110 -- 120 μ E m^{- 2} s^{- 1}), and (c) then exposed to low light (20 -- 25 μ E m^{- 2} s^{- 1}) during the O₂-consumption and H₂-production stages.