Fluoride contamination in drinking water is a global challenge due to its adverse health effects, including dental and skeletal fluorosis. The limitations of conventional removal methods, such as chemical precipitation and ion exchange, drive the search for sustainable and low-cost adsorbents. Coffee grounds, an abundant agro-industrial residue rich in carbon, show great potential as a precursor for activated carbon. Surface modification with citric acid, including its natural source from lemon juice, can significantly enhance adsorption capacity and provide a low-cost process accessible to rural communities, thereby promoting self-sufficiency in safe water treatment locally.

In this study, activated carbons derived from coffee grounds were prepared under different activation conditions (non-activated, CO₂-activated, and H₃PO₄-activated) and subsequently impregnated with citric acid or lemon extract. Adsorption experiments using sodium fluoride solutions were conducted to evaluate performance. CO₂-activated carbon impregnated with citric acid exhibited the highest adsorption capacity, reaching 0.16 mg g⁻¹ after 6 hours of contact.

The results demonstrate that agro-industrial residues, when converted into functional adsorbents, can provide viable, sustainable, and low-cost alternatives for fluoride removal in drinking water. This innovative approach reinforces the role of circular economy strategies and technological innovation in decentralized sanitation, particularly in vulnerable rural communities lacking access to conventional solutions.