Production of biological hydrogen and bacterial carotenoids with Rhodobacter sphaeroides O.U.001 in a biorefinery concept

Abstract

In this study, the goal was to produce biohydrogen and bacterial carotenoids with Rhodobacter sphaeroides O.U.001, a purple non-sulfur photosynthetic bacterium, utilizing sugar beet molasses in the context of biorefinery. First, media with different sugar concentrations (10 g/L, 20 g/L, 30 g/L, 40 g/L, 50 g/L) were prepared for bacterial growth. Then, hydrogen production was carried out using these media in anaerobic conditions in 100 ml bioreactors. After hydrogen gas was collected from the bioreactors, carotenoid extraction was performed from the remaining bacteria. As a result of the analyzes, it was found that the amount of biohydrogen and the amount of bacterial carotenoids obtained were inversely proportional to the increased sugar concentrations. The maximum hydrogen formation was detected in the medium containing 10 g/L of sugar (19.18 mL). According to the results of gas chromatography analysis, the quantity of hydrogen in the total gas was found to be around 23.6%. The highest yield of carotenoids was again obtained from bacteria reproduced in a medium containing 10 g/L of sugar (3.12 mg/g, carotenoid/dry biomass). As a conclusion, this study provides an example for the successful realization of two high value-added products within a biorefinery approach by using molasses obtained at an affordable cost.