Sustainable PUFA-Rich Lipid-Accumulating Biomass Production via Dual Waste Valorization Using Heterotrophic Microalgae Cultivated on Anaerobic Effluent and Molasses

The growing global demand for sustainable solutions necessitates innovative strategies for biomass and high-value compound production from waste. This study explores the heterotrophic cultivation of microalga <i>Chlorella</i> sp. G049 using anaerobic effluent (AE) derived from food waste and molasses as cost-effective substrates to produce polyunsaturated fatty acid (PUFA)-rich lipids while concurrently treating wastewater. Initially, one-factor-at-a-time (OFAT) experiments identified 12.5% AE and 20 g/l molasses as effective concentrations for promoting growth. Subsequently, Response Surface Methodology (RSM) was employed to optimize co-utilization of AE and molasses, maximizing biomass concentration, lipid yield, and PUFA content. The optimal conditions-18.5% AE and 18.18 g/l molasses-resulted in significantly enhanced biomass concentration (4.09 g/l), lipid yield (87.00 mg/l), and PUFA content (9.30%). The extracted lipids exhibited nutritional potential and met international biodiesel standards, with a notably high cetane number (62.95) and oxidative stability (15.27 h). Additionally, the microalgal system effectively removed chemical oxygen demand (91.79%), ammonium (63.19%), nitrate (73.21%), and phosphate (96.76%), confirming its robust wastewater remediation capacity. This dual-purpose approach points out the advantages of valorizing waste streams into value-added bioproducts and supports the advancement of circular bioeconomy principles.