Integrated UiO-66-bacterial composite for methylene blue removal: Mechanistic insights and detoxification

The integration of adsorption and biodegradation in a single biocatalytic platform offers a sustainable route for dye decolorization, yet its mechanistic understanding remains limited. In this study, a UiO-66-Pseudomonas aeruginosa biocomposite immobilized within a sodium alginate/polyvinyl alcohol (SA/PVA) matrix was used for methylene blue (MB) removal. Structural characterizations (XPS and N₂ adsorption-desorption) verified the successful incorporation of all components, forming a mesoporous network with hierarchical pores that facilitated mass transfer. The adsorption process followed pseudo-second-order kinetics and fitted the Langmuir model, achieving a maximum capacity of 18.87 mg g^-1 with CaCl₂/boric acid crosslinked beads. LC-MS analysis revealed four major degradation metabolites, supporting three pathways, namely oxidative demethylation, reduction, and ring-cleavage oxidation. Enzymatic assays confirmed the role of laccase, manganese peroxidase (MnP), and NADH-DCIP reductase in the biodegradation mechanism. In addition, phytotoxicity tests using Vigna radiata demonstrated substantial detoxification of treated effluent, indicating reduced environmental risk. These findings provide mechanistic insights into the synergistic role of UiO-66 and P. aeruginosa in enhancing both adsorption and biodegradation, highlighting their promise as an effective biocatalytic system for sustainable wastewater remediation.