Sustainable hexavalent chromium removal from aqueous solutions using novel plant-based biocoagulants: Comparative performance, mechanism elucidation, and economic evaluation

This study evaluates the effectiveness of three natural biocoagulants; walnut husk powder, avocado seed powder, and palm petiole waste for removing hexavalent chromium from aqueous solutions. Key operational parameters, including pH, coagulant dose, and particle size, were optimized using the Box-Behnken design. The biocoagulants-flocculants were comprehensively characterized before and after treatment using techniques such as XRD, FTIR, XRD, SEM-EDX, and ZP measurements to elucidate the mechanisms of chromium removal. Under optimized conditions, all biocoagulants-flocculants demonstrated significant removal efficiencies: walnut husk powder (92.47 %), avocado seed powder (ASP, 94.09 %), and palm petiole waste (PPW, 98.56 %). Cost analysis identified ASP as the most economical option, with a treatment cost of 0.0015 USD/m³. Reusability studies revealed that PPW retained the highest performance over multiple cycles, achieving 66.81 % removal efficiency after five reuse cycles. These findings highlight the efficacy, mechanisms, and scalability of these biocoagulants-flocculants as sustainable solutions for hexavalent chromium removal in water treatment applications.