Phytohormone-augmented microalgae: A dual-functional solution for pharmaceutical contaminants removal and resource...

Microalgae-based wastewater treatment offers dual advantages of carbon sequestration and resource recovery, yet its efficacy in removing pharmaceutical contaminants (PCs) remains limited. Phytohormone augmentation presents a promising strategy to enhance PCs removal and bioresource production, but the mechanisms and scalability of this approach are poorly understood. This study systematically evaluated the dual effects of seven phytohormones including indole-3-acetic acid (IAA), abscisic Acid (ABA), salicylic acid (SA), gibberellin A3 (GA3), jasmonic acid (JA), brassinolide (BR), and zeatin (ZT) on the degradation of triclocarban (TCC) and the production of bioresources in Chlorella pyrenoidosa. All phytohormones significantly improved microalgal growth, TCC removal, and biomolecule yields. SA exhibited the most balanced performance, achieving near-peak biomass yield (0.52 g L^-1, vs. ZT's 0.53 g L^-1) and TCC removal (86.2 %, vs. GA's 87.4 %), and the highest lipid productivity (4.27 mg L^-1 d^-1). Mechanistic analyses revealed that phytohormones acted via dual pathways: enhancing degradation metabolism to reduce oxidative stress and modulating calcium ion (Ca²⁺)/nitric oxide (NO) signaling to maintain reactive oxygen species (ROS) balance. Scaling up to 50-L photobioreactors treating real domestic wastewater, SA boosted removal of 16 PCs by 74.7 % (2.60-fold of the algae-only control) while elevating lipid, starch, protein, and pigment productivities by 2.86-, 4.71-, 8.91-, and 6.96-fold, respectively. Notably, 99.997 % of supplemented SA was utilized by microalgae, ensuring no secondary pollution. This work demonstrates phytohormone-augmented microalgae as a sustainable, scalable biotechnology for simultaneous wastewater purification and circular bioeconomy applications.