Effects of carbon dioxide concentration and swine wastewater on the cultivation of Chlorella vulgaris FSP-E and bioethanol production from microalgae biomass

The study investigated the potential of wastewater-derived microalgae as a cost-effective feedstock for bioethanol production. The influence of CO₂ loading, use of swine wastewater as a nutrient source, effect of micronutrients in the cultivation media, and scale-up of Chlorella vulgaris FSP-E was conducted. Results showed that 2% CO₂, 25% swine wastewater, 500 mg/L sodium nitrate, 40 mg/L K₂HPO₄, 75 mg/L MgSO₄, and 6 mg/L citric acid were optimal for maximal biomass production, nitrate removal, and carbohydrate accumulation in BG-11 medium. The maximum biomass and carbohydrate content obtained in this study were 35-fold and 60%, respectively. Scaling up to 5 L volume was challenging due to illumination, aeration, and mixing issues. The obtained carbohydrate-rich biomass was subjected to mild sulfuric acid hydrolysis and subsequently used for bioethanol fermentation. The hydrolysate was composed solely of glucose and galactose and was converted into bioethanol within 8 h by Saccharomyces cerevisiae with an ethanol yield of 0.22 ± 0.01 g ethanol per g biomass. Further exploration of effective lighting and mixing strategies are recommended to realize economically viable microalgal biofuels. © 2024 Elsevier Ltd.