Sustainable utilization of citrus peel waste: Biochar production, modification, and applications

Citrus peel waste (CPW) is generated in substantial quantities worldwide and poses an environmental burden through improper disposal; however, its high lignocellulose content makes it a promising feedstock for producing value-added biochar. This review aims to critically synthesize recent advances in CPW-derived biochar production, modification, and applications within a circular bioeconomic context. Key findings show that pyrolysis conditions, feedstock variability, and activation strategies strongly influence biochar yield, pore development, and functional chemistry. Physical, chemical, and hybrid surface modification techniques substantially increase the adsorption selectivity and efficiency. CPW-derived biochars effectively remove heavy metals, organic pollutants, and nutrient contaminants, and offer additional benefits in terms of soil improvement, carbon sequestration, and emerging biomedical applications. Despite these advantages, challenges remain regarding feedstock heterogeneity, process scalability, regeneration performance, and environmental safety. Overall, the valorization of CPW into biochar represents a sustainable pathway for waste reduction and environmental remediation, with future opportunities in advanced material engineering and alignment with global sustainability goals. • Evaluates citrus peel waste as a unique feedstock for producing high-value biochar. • Compares how pyrolysis conditions shape carbon yield, porosity, and functional groups. • Assesses modification strategies that enhance surface chemistry and reactivity. • Identifies application trends and research gaps for citrus peel waste valorization.