Concurrent removal of cetirizine hydrochloride and biodiesel accumulation in Chlorella vulgaris

The wide presence of the antihistamine cetirizine hydrochloride (CET) in the aquatic environment requires the urgent formulation of effective and sustainable repair strategies. This study explores the dual application value of Chlorella vulgaris in CET bioremediation and biodiesel feedstock production. At 1 mg/L, algae could achieve 90 % removal of CET, though as the concentration increased (10-100 mg/L), the removal efficiency dropped to 78-79 %. In addition, at extremely high concentration (100 mg/L), CET gradually inhibited the growth and function of light system II. However, it also induced beneficial metabolic reactions: the cell lipid content increased to 41.09 % of the dry weight, and it significantly improved key biodiesel indicators, such as iodine value and cold filtration blockage points. Transcriptomic profiling revealed the key role of cytochrome P450 (CYP450) with significant upregulation. Furthermore, molecular docking simulations demonstrated that CET bound steadily to CYP450 at the active site, suggesting that CET was involved in enzymatic transformation. CET stress also diverted carbon allocation from carbohydrates and proteins toward lipid synthesis, as evidenced by increased biosynthetic activity of glycolytic and triacylglycerol biosynthetic genes. Further evidence suggested that CET was biosorbed via extracellular polymers by π-π interactions. These findings collectively position C. vulgaris as an integrated platform for antihistamine pollutant removal and renewable biodiesel precursor production, a "waste-to-wealth" strategy aligned with the principles of the circular bioeconomy.