A Protocol for Elucidating the Mechanisms of Biosorption: Uptake of Cu(II) and Pb(II) by Viable Pseudomonas aeruginosa Cells

This study presents a methodological approach to elucidate the mechanisms underlying the biosorption of Cu(II) and Pb(II) by live Pseudomonas aeruginosa cells. Experiments were conducted under controlled conditions, and kinetic, equilibrium, and desorption analyses were employed to characterise both transport and attachment mechanisms. The biosorption of Pb(II) was best represented by the pseudo-second-order model, while the fit of Cu(II) was best described by both the pseudo-first- and pseudo-second-order models. The diffusion-chemisorption (D-C) model provided additional insight into transport mechanisms. The solid-phase mass transfer index (RDC) values indicated that intraparticle diffusion played a moderate role in controlling the uptake of both Cu(II) and Pb(II), with a more pronounced effect observed for Pb(II). Equilibrium data conformed best to the Sips isotherm, suggesting heterogeneous surface binding and possible cooperative adsorption. Maximum monolayer capacities were 82.48 mg/g for Cu(II) and 32.50 mg/g for Pb(II). Desorption studies enabled the quantitative attribution of metal binding to distinct interactions, including physisorption, ion exchange, complexation, and intracellular accumulation. Cu(II) biosorption was primarily governed by complexation (51%) and ion exchange (46%), while Pb(II) biosorption was largely driven by ion exchange (64%). The approach formulated in this research offers a practical framework for probing biosorption mechanisms in subsequent investigations.