Sustainable lipid production from Chlorella vulgaris USU1 strain using packed absorption column-derived effluent as carbon source for biomass generation

• C. vulgaris USU1 enables 50% CO 2 fixation with 0.00864 g/mL biomass concentration • Packed absorption column effluent supports microalgae growth at 24:0 light, 50-rpm • Unprecedented lipid yield of 31.19% surpasses prior studies 19.74-28.62% ranges • Integrated biorefinery yields IDR 3,331/L profit with residual CO 2 of 5,000 mg/L • Microalgae biomass reveals 56% protein, fatty acids dominated by palmitic (29.7%) The global surge in population and economic growth has intensified energy consumption reliant on fossil resources, leading to environmental degradation. Biogas, while offering a renewable alternative, requires CO 2 purification. This study addresses the critical knowledge gap in integrated waste-to-value approaches by investigating the synergistic coupling of biogas purification effluent utilization with Chlorella vulgaris USU1 cultivation for lipid production. This novel integration facilitates simultaneous high-quality biofuel generation and significant CO 2 utilization, thereby enabling absorbent regeneration in a closed-loop system. Utilizing packed absorption column-derived effluent (PACDE) containing KHCO 3 -PZCOO - complex solutions as the nutrient medium, this study systematically optimized cultivation parameters to maximize both biomass production and carbon utilization efficiency. Under optimized conditions (24:0 light intensity, 50-rpm agitation, 0.6 initial absorbance), the system achieved 58.3% CO 2 biofixation efficiency with a maximum biomass concentration of 8.64 g/L. Biochemical characterization revealed a composition of 23% carbohydrates and 56% proteins, with the fatty acid profile predominantly comprising palmitic (29.7%), oleic (27.6%), and linoleic (24.1%) acids. Notably, the USU1 strain demonstrated superior lipid accumulation capability with 31.19% yield, surpassing previously reported values for comparable strains. Economic analysis established favorable metrics with capital costs of IDR 4,505/L, operating expenses of IDR 1,155/L, and profit gained of IDR 8,991/L, yielding a net profit of IDR 3,331/L. Mass balance assessment demonstrated valorization of carbon inputs with approximately 2.97 kg CO 2 annually while generating 1,175 L of lipid-rich microalgae oil and 3,745 L of reusable biofertilizer effluent. This research establishes a foundation for scalable and closed-loop carbon capture and utilization technologies with implications for industrial zero-waste implementation and circular bioeconomy paradigms.