Enhancing lipid yield in freshwater microalgae through synergistic abiotic stressors for sustainable biodiesel production

Microalgae biomass shows notable promise as a liquid biofuel source with a lower carbon footprint. However, for large-scale commercialization, increasing lipid yield, especially by utilizing waste resources in a circular bioeconomy framework is critical to ensuring both efficiency and environmental sustainability. This study presents a novel approach to enhance sustainable biodiesel production from Chlorella vulgaris using composted chicken manure (CM) as the sole nutrients source through various individual and combined abiotic stressors to optimize lipid yield and biodiesel quality. It was observed that the lipid yield of microalgae cultures was increased to 0.163, 0.381, and 0.182 g/L when stressed under 4 % v/v nutrients limitation, 15 g/L of salinity, and 2 g/L of bicarbonate, respectively compared to stress-free culture (0.139 g/L). Moreover, C. vulgaris cultivated under combined stress conditions i.e., salinity (15 g/L) and bicarbonate addition (2 g/L) further enhanced the lipid yield and carbon dioxide (CO₂) fixation rate than control culture by 68.26 % and 16.64 %, respectively. Additionally, the transesterified lipid demonstrated a remarkable resemblance to corn, soybean, and sunflower oil, containing substantial quantities of palmitic acid (C16:0), oleic acid (C18:1), and linoleic acid (C18:2), thus highlighting its potential as a viable alternative to traditional vegetable oils for biodiesel conversion. Fourier transform-infrared (FT-IR) spectroscopy further confirmed the presence of ester functional groups and unsaturated bonds in the biodiesel, validating the successful transesterification and high-quality FAME profile of both control and stressed cultures.