Abstract

Photosynthetic bacterium Rhodobacter sphaeroides S10 was grown photoheterotrophically to produce hydrogen in three types of culture vessels having very different surface-to-volume ratios (S). The aim was to investigate the effect of the culture system geometry (low-aspect ratio cylindrical geometry, a rectangular or flat bottle geometry, and a tubular loop) on growth and hydrogen production as the culture vessel geometry affects the average internal irradiance. A mixed carbon substrate produced by hydrolysis of oil palm empty fruit bunch fibers was used to grow the bacterium and produce hydrogen. Internal average irradiance was shown to affect growth and hydrogen production. A tubular photobioreactor with a high surface area to culture volume ratio (S = 181.7 m⁻¹) proved to be the best culture system for producing hydrogen at a high rate. In contrast, the highest value of the maximum specific growth rate occurred in the relatively poorly lit culture of the cylindrical vessel with a comparatively low surface-to-volume ratio (S = 52.3 m⁻¹). The result suggests that irradiance regimen is a key factor controlling the switch from biomass production to hydrogen production.