Several microalgal species, including Chlamydomonas sp. and Chlorella sp., have shown their capability of producing molecular H2 directly through the utilization of algal fermentative metabolisms. However, the enzyme responsible for H2 production, hydrogenase, is extremely sensitive to O2 and thus effective oxygen control is required to achieve sustainable H2 production. While sulfur deprivation is a well-established strategy for oxygen control in photolysis, sulfur control requires specific synthetic feedstocks and identifying effective alternative oxygen regulation strategies would be of benefit to wastewater applications. The objective of the study was to achieve complete inhibition of O2 evolution for microalgal photolysis-mediated biohydrogen production in a continuous mode using synthetic acetate-enriched fermenter effluent. To counteract natural metabolism of O2 evolution in photosystem II (PSII), we utilized acetic acid, which can be found in fermenter effluent, as an oxygen regulator for photosynthetic bio-H2 production using two microalgal species, C. reinhardtii and C. vulgaris. It was hypothesized that acetate can occupy the Cl- binding site at the oxygen evolving complex (OEC) in photosystem II (PSII). It was found that acetate-enriched wastewater promotes oxygen depletion under continuous algal H2 photobioreactors (PBR), producing average hydrogen of 108 ± 4 µmol/L for C. reinhardtii and 85 ± 15 µmol/L for C. vulgaris at 100 µmol/m2/s with a 15 day duration and without sulfur deprivation. An upward (210 µmol/m2/s) or downward (48 µmol/m2/s) shift in the light intensity gradually led to a decrease in the enhanced extent of H2 production, suggesting that light intensity is one of the important parameters for microalgal H2 production. The H2ase activity for C. reinhardtii and C. vulgaris showed stable values (41.6 ± 2.3 and 38.8 ± 1.2 U/mg of protein) during the 15 days, correlating with the H2 production. Better understanding on the role of acetate on O2 regulation in PSII and light intensity in natural environments is expected to lead algal-driven bio-H2 production technologies to significant advancements.

Microalgal photolysis-mediated biohydrogen production in acetate-enriched wastewater

2019 Spring National Meeting

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