Effects of different sugar sources on photoheterotrophic hydrogen production by Chlorella vulgaris

1 Effects of different sugar sources on photoheterotrophic hydrogen production by Chlorella vulgaris Isabela Calegari Moia1, Raffaella Margherita Zampieri1,2, Eleftherios Touloupakis1,* 1Research Institute on Terrestrial Ecosystems, National Research Council, Via Madonna del Piano 10, 50019, Sesto Fiorentino, FI, Italy; 2Department of Agriculture, Food, Environment and Forestry, UniversiHydrogen (H₂) production by microalgae represents a promising approach to renewable energy generation. In this study, the photoheterotrophic H₂ production of Chlorella vulgaris was investigated using three different sugar sources: glucose, sucrose, and fructose. Cultures were grown in a 0.5 L photobioreactor under controlled light and temperature, and assessed for H₂ yield, production rate, nutrient uptake, biomass accumulation, and light conversion efficiency (LCE). Glucose yielded the highest H2 production, producing 461.56 mL H₂ L⁻¹ (48.76 mL H₂ g⁻¹ glucose), with a maximum rate of 22.62 mL H₂ L⁻¹ h⁻¹ and an LCE of 7.09%, likely due to its high uptake and efficient metabolism. Sucrose and fructose produced lower yields of 24.36 mL H₂ L⁻¹ (29 mL H₂ g⁻¹ sucrose) and 52.2 mL H₂ L⁻¹ (17.63 mL H₂ g⁻¹ fructose), respectively, with reduced production rates (6.96 and 13.92 mL H₂ L⁻¹ h⁻¹, respectively) and LCEs of 2.18% and 1.23%, respectively. Sugar consumption reached 9.42 g L⁻¹ for glucose, 0.84 g L⁻¹ for sucrose, and 2.96 g L⁻¹ for fructose; in all cases, the initial sugar concentration was 10 g L⁻¹. Glucose also stimulated higher nutrient uptake, with 1.36 g L⁻¹ nitrate, 137.85 mg L⁻¹ phosphate, and 55.25 mg L⁻¹ sulfate consumed during H2 production. This study experimentally compares the effects of various sugar sources on photoheterotrophic H₂ production in C. vulgaris, elucidating the role of organic carbon availability in modulating microalgal metabolism and bioH2 yield. The findings highlight that the choice of carbon source is a critical determinant of photoheterotrophic H₂ production efficiency under nutrient-replete conditions.