Isolation of a Metal-Tolerant Serratia Marcescens for Cu(II) and Pb(II) Biosorption: Elucidating Transport and Attachment Mechanisms

This study explores the biosorptive potential of a metal-tolerant strain of Serratia marcescens isolated from soil near an underground fuel storage tank, for the removal of Cu(II) and Pb(II) from aqueous solutions. Batch biosorption experiments were conducted to assess kinetic and equilibrium behaviour. The Weber and Morris intraparticle diffusion and the diffusion-chemisorption (D-C) models were applied to elucidate transport mechanisms. Langmuir and the Freundlich isotherms were used for equilibrium modelling. Individual and sequential desorption tests using distilled water, CaCl₂, EDTA and HCl were performed to identify the nature of attachment mechanisms. Both metals reached equilibrium within 60 min, with Cu(II) showing a faster uptake rate (half-time 2.2 min) than Pb(II) (13.9 min). Surface adsorption and intracellular diffusion were identified as the dominant transport pathways, with the D-C model indicating a stronger diffusion contribution for Pb(II) (R_DC = 0.392) than for Cu(II) (R_DC = 0.156). Langmuir analysis yielded monolayer capacities of 34.4 mg/g for Cu(II) and 22.2 mg/g for Pb(II). Desorption studies using distilled water, CaCl₂, EDTA and HCl provided insight into binding mechanisms. CaCl₂ and EDTA each desorbed 47.3% of Cu(II), suggesting a notable influence by ion-exchange and complexation, while HCl released 4.5%, consistent with intracellular accumulation. This study highlights the multifaceted biosorption of Cu(II) and Pb(II) by S. marcescens. Integrating kinetic, equilibrium and desorption analyses provide mechanistic clarity, which guides optimization and regeneration strategies and strengthens the biosorbent’s practical value for cost-effective, sustainable heavy metal remediation.