Effect of post-treatment process of microalgal hydrolysate on bioethanol production

Microalgae accumulate abundant lipids and are a promising source for biodiesel. However, carbohydrates account for 40% of microalgal biomass, an important consideration when using them for the economically feasible production of biodiesel. In this study, different acid hydrolysis and post-treatment processing of Chlorella sp. ABC-001 was performed, and the effect of these different hydrolysates on bioethanol yield by Saccharomyces cerevisiae KL17 was evaluated. For hydrolysis using H₂SO₄, the neutralization using Ca(OH)₂ led to a higher yield (0.43 g ethanol/g sugars) than NaOH (0.27 g ethanol/g sugars). Application of electrodialysis to the H₂SO₄ + NaOH hydrolysate increased the yield to 0.35 g ethanol/g sugars, and K⁺ supplementation further enhanced the yield to 0.41 g ethanol/g sugars. Hydrolysis using HNO₃ led to the generation of reactive species. Neutralization using only NaOH yielded 0.02 g ethanol/g sugars, and electrodialysis provided only a slight enhancement (0.06 g ethanol/g sugars). However, lowering the levels of reactive species further increased the yield to 0.25 g ethanol/g sugars, and K⁺ supplementation increased the yield to 0.35 g ethanol/g sugars. Overall, hydrolysis using H₂SO₄ + Ca(OH)₂ provided the highest ethanol yield, and the yield was almost same as from conventional medium. This research emphasizes the importance of post-treatment processing that is modified for the species or strains used for bioethanol fermentation.