Valorization of banana peel and orange peel as low-cost biosorbents for Cu(II), Cr, and Pb(II) removal from aqueous solutions

The persistent presence of heavy metals in wastewater presents major threats to the environment and public health because of their toxic nature, non-biodegradability, and bioaccumulation. Conventional treatment methods are often costly and complex, highlighting the need for low-cost and sustainable alternatives. This experimental study explores the potential of banana peel (BP) and orange peel (OP) as eco-friendly biosorbents for eliminating Cu(II), total dissolved chromium (Cr), and Pb(II) from aqueous solutions, with potential relevance for low-cost wastewater pre-treatment applications. Surface characterization using SEM revealed porous, irregular morphologies favorable for adsorption, while FTIR analysis revealed the presence of key functional groups, including hydroxyl, carboxyl, and carbonyl, that play a vital role in metal ion binding. Batch adsorption experiments demonstrated that metal removal efficiency increased with higher biosorbent doses and decreased with increasing initial concentrations, indicating the influence of biosorbent availability and surface saturation. Under operational conditions, maximum percentage removals of Cu(II) (up to 91.8% with BP and 74.2% with OP), Cr (up to 73.7% with BP and 86.8% with OP), and Pb(II) (up to 95.0% with BP and 79.1% with OP) were achieved. Solution pH strongly influenced adsorption behavior, with Cr removal favored under acidic conditions, while Cu(II) and Pb(II) exhibited higher removal efficiencies near neutral pH. Post-adsorption SEM and FTIR analyses provided mechanistic insights, indicating surface coverage, pore occupation, and functional group involvement through ion exchange and surface complexation mechanisms. Overall, untreated fruit peels demonstrate strong potential as low-cost biosorbents for heavy-metal-laden wastewater. Future studies should focus on determining adsorption capacities under optimized conditions, supported by isotherm, kinetic, and thermodynamic modeling, as well as evaluating regeneration and reusability through multiple adsorption-desorption cycles. Spent biosorbent management strategies and comparative assessment with existing literature will further strengthen practical applicability and circular-economy relevance.