Transforming Recycled Coffee Grounds into High-Performance Bio-Adsorbents for Efficient Removal of Toxic Chromium (Cr(VI)) from Water

This study explores the potential of using spent coffee grounds (SCG) treated with Ca(OH)₂ as an innovative and sustainable adsorbent material for removing toxic chromium ions (Cr(VI)) from water. Unlike conventional adsorbents, which often require complex synthesis processes and may generate secondary pollution, this study highlights the novel approach of utilizing waste coffee grounds a widely available and low-cost agricultural byproduct enhanced through a simple yet effective chemical modification process. The coffee grounds were processed through a series of preparation steps, including washing, drying, sieving, and chemical treatment with Ca(OH)₂ solutions at varying concentrations to enhance their surface properties and adsorption capacity. Adsorption experiments were systematically conducted under diverse conditions, including contact time, pH, adsorbent dosage, temperature, and initial Cr(VI) concentration, to determine the optimal parameters for effective chromium removal. The results demonstrated that Ca(OH)₂ treatment significantly altered the physicochemical characteristics of the coffee grounds, improving their porosity and increasing the availability of active sites for Cr(VI) adsorption. Under optimal conditions contact time of 180 minutes, pH 3, an adsorbent dosage of 1 gram, and a temperature of 313 K the modified SCG achieved a maximum adsorption capacity (qmax) of 19.84 mg/g, outperforming many previously reported bio-adsorbents. Furthermore, desorption studies indicated that HNO₃ was the most effective regenerating agent, achieving a desorption efficiency of 91.60%. However, the reusability assessment revealed a gradual decline in adsorption efficiency over multiple cycles, decreasing from 90.89% in the first cycle to 44.08% after ten cycles. This research provides a pioneering contribution to the field of wastewater treatment by demonstrating a practical and eco-friendly method for upcycling waste coffee grounds into a high-performance adsorbent. The study not only validates the feasibility of using chemically modified SCG for heavy metal removal but also underscores its potential scalability for real-world applications in environmental remediation. By integrating waste valorization with sustainable water purification strategies, this work opens new avenues for the development of green, cost-effective, and efficient adsorbent materials in the fight against water pollution.