Continuous photosynthetic biohydrogen production from acetate-rich wastewater: Influence of light intensity

Abstract

Photo-biohydrogen by microalgae is attractive sustainable energy caused by the utilization of solar energy and water. However, due to oxygen (O2) sensitive hydrogenase (HydA) activity, effective control of O2 and light intensity is critical for achieving sustainable photosynthetic hydrogen (H2) production. Here we demonstrate continuous algal H2 production using acetate-enriched fermenter effluent, achieving the complete O2 cessation without sulfur depletion. Average H2 production of 108 ± 4 μmol L−1 for Chlamydomonas reinhardtii and 88 ± 7 μmol L−1 for Chlorella sorokiniana at 100 μmol m−2 s−1 were observed for 15 days, respectively. The highest light energy to H2 energy conversion efficiency (LHCE) of 1.61% for C. reinhardtii and 1.06% for C. Sorokiniana was obtained under low light intensity (50 μmol m−2 s−1) but the LHCE decreased with the increase of light intensity followed by photoinhibition, which led to a decrease of HydA activity and H2 production. Low H2 production was observed at 50 μmol m−2 s−1 under the highest LHCE, in which microalgae exhibited photoinhibition biomass growth kinetics to produce chlorophyll a (Chl a) for electron generation. These results demonstrate that light is a feasible strategy for producing electron for H2 production under anoxygenic photosynthesis.