Methanol-driven co-metabolic enhancement of benzotriazole and 5-chlorobenzotriazole degradation by Chlorella pyrenoidosa: Mechanisms, transformation pathways, and metabolic insights

Benzotriazoles (BTRs), widely used as tire additives, pose a significant challenge as persistent aquatic pollutants due to their recalcitrance to conventional biological degradation. This study elucidated methanol (ME)-enhanced co-metabolic degradation of 1H-benzotriazole (BT) and 5-chlorobenzotriazole (CBT) by green microalgae. Among the six microalgal species evaluated, Chlorella pyrenoidosa demonstrated superior removal of BT and CBT under 1 % ME supplementation, achieving efficiencies of 33.50 % and 89.67 %, respectively. ME functioned as an electron donor, which favored the reductive dechlorination of CBT, leading to a 2.85-fold higher removal efficiency compared to BT. Biotransformation was identified as the dominant removal mechanism, with 11 and 10 transformation products (TPs) detected for BT and CBT, respectively. An integrated analysis of TPs and transcriptomic data revealed that ME activates a metabolic enzyme-photosynthetic machinery, enhancing electron transport, energy generation, cytochrome P450 (CYP450) expression, and extracellular polymeric substance (EPS) production, thereby facilitating efficient pollutant removal. The proposed degradation pathways further confirmed the role of ME in facilitating specific biotransformation reactions. These findings provide mechanistic insights and establish a theoretical foundation for the development of ME-microalgae co-metabolism systems as a sustainable technology for remediating persistent pollutants in aquatic ecosystems.