Comprehensive Study on the Application of Orange Peel Waste as a Sustainable Bio-adsorbent for Heavy Metal Remediation in Aquatic Ecosystems

Abstract Heavy metal pollution in aquatic environments remains a major global ecological crisis due to the high toxicity, persistence, and bioaccumulative nature of these elements. Conventional industrial wastewater remediation techniques are constrained by steep operating costs and secondary toxic sludge generation. This study comprehensively evaluates the feasibility of raw and modified orange peel (OP) powder as an eco-friendly, low-cost bio-sorbent for removing dangerous heavy metals such as Lead (Pb²⁺), Copper (Cu²⁺), Cadmium (Cd²⁺), and Chromium (Cr⁶⁺) from simulated and industrial wastewater streams. Characterization studies via Fourier Transform Infrared (FTIR) spectroscopy and Scanning Electron Microscopy (SEM) reveal a highly porous cellulosic matrix rich in carboxyl, hydroxyl, and methoxy functional groups derived from native pectin and lignin components. Batch adsorption investigations were executed to evaluate the influence of solution pH, biosorbent dosage, contact time, and initial heavy metal concentration. Experimental kinetics align with the pseudo-second-order mechanism, suggesting chemical adsorption (chemisorption) as the primary rate-limiting step. Equilibrium isotherm datasets conform closely to the Langmuir model, indicating monolayer adsorption onto defined active binding sites. The chemical modification of raw orange peel with dilute acids (HCl) or alkali salts significantly upgrades the active surface configurations, boosting target metal uptake. Thermodynamic parameter indices confirm the spontaneous, feasible, and predominantly endothermic nature of the biosorption process. This work establishes agricultural waste valorization as a robust contributor to circular economies and green water purification infrastructures.