Enhancing wastewater remediation in microalga Euglena gracilis: The role of trivalent cerium (Ce³⁺) as a hormonal effect factor and its metabolic implications

This study explored the effects of trivalent cerium (Ce³⁺) as a hormonal effect factor on microalga Euglena gracilis in domestic wastewater treatment. It was discovered that 12.50mg/L Ce³⁺ markedly enhance E. gracilis dry weight (by 63.44%, P < 0.05) and boost its efficiency in extracting key water quality indicators such as total nitrogen (TN) by 66.08% (p < 0.05), total phosphorus (TP) by 37.17% (p < 0.05), ammonia nitrogen (NH4+-N) by 39.90% (p < 0.05), and chemical oxygen demand (COD) by 97.17% (p < 0.05) from wastewater. Metabolomic analysis revealed that Ce³⁺ treatment significantly alters E. gracilis's metabolic profile, notably in lipid metabolite synthesis. This treatment increased the production of essential membrane lipid metabolites like phosphatidylglycerol and phosphatidic acid, vital for cellular membrane integrity. Additionally, Ce³⁺ stimulated the synthesis of certain antioxidant dipeptides, reducing wastewater-induced reactive oxygen species (ROS) levels. This treatment improved not only nutrient removal efficiency from wastewater by E. gracilis but also its conversion to high-value metabolic products, such as paramylon and lipids. These findings highlight Ce³⁺'s pivotal roles in augmenting E. gracilis's wastewater treatment efficacy and environmental resilience, offering significant insights for microalgae's use in environmental management and bioenergy.