A Circular Economy Approach: Transforming Pumpkin (Cucurbita pepo) Peel Waste into a Low-Cost Adsorbent for Water Purification

The widespread contamination of aqueous ecosystems by synthetic dyes, discharged from industries such as textiles and printing, poses a severe environmental and health risk due to their toxicity and recalcitrance. Conventional treatment methods often suffer from high operational costs and the generation of secondary pollutants. Addressing this global challenge, this study explores the valorization of agro-industrial Cucurbita pepo peel waste into low-cost, effective bioadsorbents. Embracing a circular economy model, we transformed this abundant by-product into three distinct materials: raw untreated biomass (CPP-R), and two thermally treated versions produced via pyrolysis at 200°C (CPP-200) and 400°C (CPP-400).

Comprehensive physicochemical characterization using FTIR, laser granulometry, and point of zero charge (PZC) analysis was conducted. The results confirmed that thermal treatment significantly modifies the material's surface chemistry, increasing the presence of key functional groups and altering its porous structure. The materials' efficacy in removing Methylene Blue (MB) from aqueous solutions was then assessed in a batch system, systematically optimizing parameters such as pH, contact time, and initial concentration.

Our findings reveal that thermal treatment markedly enhances adsorption capacity, with the biochar produced at 400°C (CPP-400) demonstrating superior performance. Adsorption kinetics were best described by the pseudo-second-order model, indicating that chemisorption is the dominant rate-limiting mechanism. Furthermore, equilibrium data correlated strongly with the Freundlich isotherm, suggesting multilayer adsorption onto a heterogeneous surface with energetically diverse binding sites. This research highlights a viable pathway for converting agricultural by-products into a valuable resource for environmental remediation.