Spent Coffee Grounds and Their Derivatives as Biosorbents in Wastewater Treatment and Gas Purification

Abstract

Spent coffee grounds (SCGs), a ubiquitous and renewable agricultural waste, have emerged as a promising biosorbent for environmental remediation. This review provides a comprehensive overview of the application of SCG-derived materials in wastewater treatment and gas purification. We systematically summarize their physicochemical characteristics, adsorption performance towards diverse contaminants, and underlying mechanisms. Specifically, modification strategies of raw SCGs are discussed in detail, including chemical modifications (e.g., degreasing/alkali/acid/organic solvent/metal oxide treatment), thermochemical conversions (e.g., pyrolysis, hydrothermal carbonization, and activation), and the fabrication of composites with natural or synthetic materials such as chitosan, clay minerals, and agricultural/industrial wastes. These approaches effectively optimize pore structure, enrich surface functionalities, and enhance selectivity and adsorption capacity. Particular attention is devoted to SCG-derived activated carbon and composites for capturing gaseous pollutants (e.g., CO2, H2S, PH3, and VOCs). Techno-economic analysis of SCG-derived materials production is discussed to evaluate their commercial viability and overall sustainability. Finally, critical research gaps are identified, and future perspectives are proposed, emphasizing the elucidation of adsorption mechanisms, rational material design, and rigorous techno-economic and life-cycle assessments. This review underscores the potential of SCG-based materials as low-cost, high-performance alternatives to conventional adsorbents, aligning with the principles of a circular economy and environmental sustainability.