Transformation of chloroxylenol in real sewer sediments: Key adsorption sites and CYP450-catalyzed biodegradation

The widespread discharge of emerging micropollutants (EMs) into sewer systems has raised serious environmental concerns throughout the world. However, the transformation mechanisms underlying the accumulation of EMs in sewer sediments remain largely unexplored. This study investigated the transformation fate and mechanisms of chloroxylenol (PCMX) in sewer sediments. Results demonstrated that adsorption and biodegradation were the predominant routes for PCMX removal in sewer sediments, accounting for 51.6 % and 38.6 % of the bulk removal, respectively. The adsorption process adhered to a pseudo-second-order kinetic model, involving three phases including surface diffusion, intraparticle diffusion, and equilibrium. Increased secretion and structural loosening of extracellular polymeric substances (EPS) promoted PCMX adsorption, largely due to the abundant existence of hydrophobic functional groups. Among these, the amino-N of extracellular protein had the most significant effect on PCMX adsorption. For comparison, biodegradation played a key role during a long-time operation, ascribing to the contribution of cytochrome P450 (CYP450) monooxygenase. Molecular docking and dynamics simulation revealed that van der Waals and hydrogen bonding played crucial roles in PCMX adsorption, and Leu341, Phe322, and Thr79 (key CYP450 residues) provided efficient active binding sites. These findings offer in-depth insights into the interplay between physicochemical and biological processes in EMs transformation.