Statistical optimization, kinetic and equilibrium studies of Cu 2+ biosorption using apple pomace

Copper (Cu2+) contamination in industrial wastewater poses serious environmental and public health risks, especially in water-scarce countries such as South Africa. Concurrently, large quantities of apple pomace, an agro-industrial by-product, are generated annually and commonly disposed of by landfilling or incineration, creating additional environmental concerns. This study evaluates apple pomace as a low-cost, sustainable biosorbent for the removal of Cu2+ ions from wastewater. Response Surface Methodology (RSM), using central composite design, optimized initial Cu2+ concentration, adsorbent dosage, and particle size under two scenarios in Design-Expert 13. In the first scenario, targeting maximum overall removal, the optimal conditions were 14.47 mg/L Cu2+, 0.57 g of adsorbent, and a particle size of 125 µm, achieving 89.39% removal. In the second scenario, with 50 mg/L Cu2+, a 1 g dosage, and a particle size of 75 µm, 83.43% removal was achieved. Adsorption equilibrium followed the Langmuir isotherm (R2 = 0.984), and the Elovich model best described the kinetics. FT-IR and SEM-EDX analyses confirmed the presence of active functional groups, a porous surface morphology, and an elemental composition favorable for Cu2+ uptake. The findings demonstrate the potential of apple pomace for sustainable wastewater treatment, with future work focusing on regeneration, multi-metal systems, and fixed-bed applications.