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

Abstract Hydrogen (H 2 ) production by microalgae represents a promising approach to renewable energy generation. In this study, the photoheterotrophic H 2 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 H 2 production, producing 461.56 mL H 2 L −1 (48.76 mL H 2 g −1 glucose), with a maximum rate of 22.62 mL H 2 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 H 2 L −1 (29 mL H 2 g −1 sucrose) and 52.2 mL H 2 L −1 (17.63 mL H 2 g −1 fructose), respectively, with reduced production rates (6.96 and 13.92 mL H 2 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 H 2 production. This study experimentally compares the effects of various sugar sources on photoheterotrophic H 2 production in C. vulgaris , elucidating the role of organic carbon availability in modulating microalgal metabolism and bioH 2 yield. The findings highlight that the choice of carbon source is a critical determinant of photoheterotrophic H₂ production efficiency under nutrient-replete conditions.