Renewable algal photo H₂ production without S control using acetate enriched fermenter effluents

Renewable energy production using microorganisms is one of the challenging issues for environmental sustainability. Algal hydrogen (H-2) production has often been achieved by sulfur (S) and chloride ion (Cl-) deprivation in a growth medium; however, it may not be realistic to control S or Cl- concentrations in natural sources (e.g., wastewater). In this study, two different green algal species, Chlamydomonas reinhardtii and Chlorella sorokiniana were selected and their photosynthetic activities were compared with different acetate/Cl- ratios both in batch and continuous modes. At 150 of acetate/Cl- ratio, the H-2 production rates were 0.25-0.33 mmol L-1 min(-1) for C. sorokiniana and 0.20-0.38 mmol L-1 min(-1) for C. reinhardtii, respectively. The hydrogenase (HydA) reactivation and photosystem II (PSII) inhibitor test revealed that biohydrogen production by algae is due to photosynthetic activity. It was found that maintaining acetate/Cl- ratios greater than 60-100 leads to continuous O-2 depletion and thus renewable H-2 production for both algal species. Molecular dynamics (MD) simulations of hydrogen bonding between Y-z and His(190) in PSII supported O-2 inhibition using acetate. Using fermenter effluents, C. sorokiniana and C. reinhardtii showed a successful continuous H-2 production of similar to 80 mmol L-1 and similar to 95 mmol L-1, respectively, for 15 days. (C) 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.