Evaluation of Marble Industry Waste for Chlorella vulgaris Cultivation in Third-Generation Bioethanol Production

Abstract

The increasing global energy demand and environmental concerns related with fossil fuel consumption have intensified interest in renewable biofuel resources. Third-generation biomass, particularly microalgae, has gained attention due to its high growth rate, carbohydrate-rich composition, and lignin-free cell wall, which enables efficient saccharification with reduced pretreatment requirements. In this study, C. vulgaris cultivated in the presence of marble waste was evaluated as a feedstock for bioethanol production. Mixotrophic cultivation was carried out for 14 days, and the highest biomass concentration (0.39 g/L) was obtained at a marble waste concentration of 1 g/L, whereas biomass production under photoautotrophic conditions was only 0.33 g/L. To enhance fermentable sugar concentration, 5 g/L of microalgal biomass was subjected to alkaline H₂O₂ (1, 2.5, 5, and 7.5%) and dilute H₂SO₄ pretreatment methods. Among the methods, dilute acid pretreatment with 1% H₂SO₄ resulted in the highest reducing sugar concentration. Bioethanol production by S. cerevisiae was subsequently investigated at initial biomass concentrations of 5, 10, and 15 g/L, which yielding maximum ethanol concentrations of 1.48 ± 0.03, 2.18 ± 0.04, and 3.08 ± 0.05 g/L, respectively, after 24 hours of fermentation.