Enhancing biomass and lipid productivity of Chlorella sp. BRE5 with surplus phosphorus supply implementing semi-continuous cultivation in the indoor and outdoor reactor system
摘要
In this work, a semi-continuous cultivation strategy (SCCS) with surplus phosphorus (P) supply was studied to evaluate the performance of Chlorella sp. BRE5 for enhanced biomass and lipid production. Different P doses (250–1000%) were supplied at various stages of cultivation (9th, 15th, and 21st day) under the shake-flask study. The highest total biomass yield (8.36 g L−1) was achieved with 750% P, when supplemented from the 15th day. High P availability promotes nucleic acid, ATP, and phospholipids synthesis, providing energy for cell growth, thereby enhancing biomass and lipid production. The optimized strategy was further scaled up in an indoor photobioreactor (PBR-3) and outdoor open raceway pond (ORP-3), where the total biomass yields in PBR (9.38 g L−1) and ORP (4.36 g L−1) were higher than in reactors without surplus P supply (PBR-2 and ORP-2) and batch (PBR-1 and ORP-1) systems. Lipid content (26.9%) and lipid productivity (93.3 mg L−1 d−1) grown under PBR-3 were 1.27 and 2.68 times higher, respectively, than in ORP-3. Although the carbohydrate content in ORP-3 (32.7%) was slightly higher than PBR-3 (31.8%), overall carbohydrate productivity (52.8 mg L−1 d−1) was found to be lower due to uncontrolled environmental conditions. Fatty acid profile under optimized P strategy primarily comprises C16-C18 (92.9–95.6%), with high saturated fatty acids, indicating microalgal oil is suitable for high-quality biofuel production. This study demonstrates a scalable SCCS with surplus P supply for improved microalgae biomass and lipid production, while supporting nutrient recovery from wastewater and sustainable biofuel production.