Influence of light-dark cycles on hydrogen production from sugarcane bagasse by Rhodobacter sphaeroides

Abstract

Photo-fermentative hydrogen production from lignocellulosic biomass offers a clean, efficient, and eco-friendly alternative for energy generation. Large-scale photo-fermentative hydrogen production, ideally conducted under outdoor conditions is influenced by the daily light-dark cycle. This study examines the effect of a 12-h light-dark cycle (12L/12D) on hydrogen production by Rhodobacter sphaeroides HY01 using sugarcane bagasse (SCB), comparing it with continuous light (CL) conditions. The results show that bacterial growth was not significantly affected by the light-dark cycle. The optical density (OD₆₆₀) of the culture reached 3.25 under 12L/12D and 3.49 under CL. However, total hydrogen yield decreased substantially under the light-dark cycle, from 6020.11 ± 54.71 mL/L in CL to 4242.73 ± 182.03 mL/L in the 12L/12D condition. Additionally, the rate of hydrogen production was higher under CL (119.78 ± 4.82 mL/(L·h)) compared to 12L/12D (60.97 ± 7.27 mL/(L·h)), while the lag phase was shorter under CL, at 17.25 ± 1.04 h, versus 20.37 ± 3.98 h under 12L/12D. Gas chromatography-mass spectrometry (GC-MS) analysis identified lactic acid, butyric acid, and ethanol as the primary soluble metabolites, with ethanol yield under 12L/12D being approximately half of that under CL. Notably, light conversion efficiency (LCE) for hydrogen production was significantly enhanced under the light-dark cycle, showing a 1.36-fold increase compared to CL conditions. These findings not only contribute to the understanding of the influence of light cycles on biohydrogen production but also support the development of more efficient and cost-effective biohydrogen systems for sustainable energy production.