Paracetamol biodegradation in an ethane-based membrane biofilm reactor

• An ethane-fed MBfR achieved stable and near-complete PCT removal. • PCT degradation was dominated by the hydroquinone pathway in the biofilm. • Mycobacterium and Mycolicibacterium seemed to play key roles in PCT transformation. • Rapid detoxification prevented toxic BQ accumulation during PCT degradation. • Oxidative-stress self-regulation supported sustained PCT degradation. Paracetamol (PCT) is a ubiquitous pharmaceutical contaminant, yet the detoxification mechanisms of PCT and its biotransformation products remain insufficiently understood. In this study, an ethane-fed membrane biofilm reactor (MBfR) was developed to investigate PCT removal, transformation pathways, and microbial stress-regulation strategies. The MBfR achieved consistently high PCT removal (>99%, with a removal rate of 2687.6 ± 97.9 μg/(L·d)) under increasing influent concentrations without accumulation of toxic aromatic intermediates. Transformation analyses revealed that PCT degradation was dominated by the hydroquinone pathway, characterized by rapid conversion to p-aminophenol (PAP), followed by efficient ring cleavage and downstream assimilation. Metagenomic and metatranscriptomic analyses identified Mycobacterium and Mycolicibacterium as potential key functional taxa involved in PCT transformation, supported by the enrichment and expression of genes encoding pyrazinamidase. Importantly, the biofilm exhibited a self-regulating defense against quinonoid stress, integrating fast reductive conversion of p-benzoquinone (BQ) to hydroquinone (HQ) with thiol-mediated conjugation and coordinated antioxidant systems, thereby preventing electrophilic and oxidative damage and sustaining high degradation activity. This study provides new mechanistic insight into how ethane-driven aerobic biofilms couple pharmaceutical degradation with redox control, oxidative-stress control and conjugative detoxification, highlighting MBfR systems as a robust and safe platform for the treatment of pharmaceutical-contaminated water systems.