Photocatalytic Degradation of Metformin Using ZnO/UV System: Kinetic Study and Transport Modeling in Porous Media

Abstract

The occurrence of pharmaceutical contaminants in aquatic and terrestrial environments has become a major environmental concern due to their persistence, continuous release, and biological activity at low concentrations. Metformin hydrochloride, a widely prescribed antidiabetic drug, is frequently detected in water and soil systems owing to its high consumption and resistance to biodegradation. This work couples photocatalysis with soil transport modeling to assess removal efficiency and environmental fate.This study investigates the transformation of metformin from aqueous solutions using ZnO-assisted photocatalysis under UV irradiation, combined with an assessment of its transport behavior in porous media. The influence of key operational parameters, including catalyst loading, initial concentration, and pH, was systematically evaluated. Under optimal conditions (pH 9.7, 0.3 g L⁻¹ ZnO), a removal efficiency of 77% was achieved within 180 min. Kinetic analysis confirmed pseudo-first-order behavior, demonstrating the effectiveness of photocatalysis compared to adsorption alone. It should be noted that UV–Vis spectrophotometry reflects primary transformation rather than complete degradation due to the possible formation of transformation products such as guanylurea. The transport of metformin was further simulated in light sand and biosolid-amended soil using a nonlinear physical nonequilibrium (PNE) model. Breakthrough curve analysis revealed rapid transport with limited retention in lignt sand, whereas delayed migration and enhanced sorption were observed in biosolid-amended soil, indicating nonlinear sorption behavior. These findings highlight the importance of integrating advanced treatment processes with subsurface transport analysis to provide a more comprehensive environmental risk assessment of pharmaceutical contaminants.