Bio-hydrogen production by Chlorella vulgaris under diverse photoperiods

The hydrogen production by Chlorella vulgaris exposed to four different light patterns was explored. Cultures of immobilized, sulfur-deprived cells were purged with N2 and either kept in the dark for 72 h, kept in the dark for 24 h before being exposed to light (intensity of 120 μ mole/m2/s) for 72 h, exposed to light for 72 h, or kept in the light for 24h before being subjected to darkness for 48 h. The latter condition provided for the highest total hydrogen production of 530±5 ml/l of medium and a maximum hydrogen release rate of 34.8 ml/h/l. Growth for 72 h under partial light conditions was essential for continuous and enhanced hydrogen production. The addition of glucose to the sulfur-deficient medium increased hydrogen production by 18 times under partial light condition. To increase the hydrogen productivity, a carbon source may be added to enhance hydrogen production.