Characterization of cell growth and photobiological H2 production of Chlamydomonas reinhardtii in ASSF industry wastewater

• Cells can grow in wastewater medium with the rate as high as 0.19 × 106 cells/h.
• Cell density reached 8.9 × 106 cells/mL in wastewater medium grown culture.
• An 8.5 folds higher photo-H2 production was obtained in wastewater culture.

Photobiological H2 production in microalgae is a promising approach for the development of alternative clean and renewable energy. As a unicellular green alga, Chlamydomonas reinhardtii is regarded as an ideal candidate for sustainable photo-H2 production. However, growth and photo-H2 producing are still expensive and energy extensive. Wastewater has been suggested as an economical resource for microalgae growth and biofuels production. In this study, we characterized the cell growth and photo-H2 production of C. reinhardtii CC503 cultured in waste water from pressing process of fermented sweet sorghum stalks during Advanced Solid State Fermentation (ASSF). The maximal cells concentration reached 8.9 × 106 cells/mL in ASSF wastewater medium (AWM) with the fastest growth rate of 0.19 × 106 cells/h, compared to 18.2 × 106 cells/mL and 0.36 × 106 cells/h in TAP medium and to 1.3 × 106 cells/mL and 0.02 × 106 cells/h in BGII medium respectively. The optimized concentration of wastewater for algae cells growth was determined to be 13.3% (7.5 folds dilution), under which, surprisingly the photosynthetic H2 evolution was increased by more than 700% compared to the cells grown in TAP medium. This system appears to be a good strategy for the development of an economical microalgal photobiological H2 production scheme. Finally, the possible mechanism for such an H2 enhancement was identified as the reduction of PSII activity in AWM grown cells.