Biotransformation of Residual Avocado Biomass into Humic Substances Through Composting: Kinetic Foundations and Process-Control Strategies

Residual avocado biomass, primarily peel and seed generated during industrial processing of Persea americana Mill., represents an abundant agro-industrial residue with considerable potential for sustainable valorization. This review critically examines the biotransformation of residual avocado biomass into humic substances (HS) through composting, integrating current knowledge on substrate composition, microbial succession, biodegradation kinetics, humification mechanisms, and process-control strategies. A systematic literature review was conducted following the PRISMA framework, enabling the identification and critical evaluation of recent advances in composting technologies, kinetic modeling, and humification processes specific to avocado residues. Particular emphasis is placed on the influence of key operational variables—including temperature, moisture, aeration, C/N ratio, pH, and microbial activity—on organic matter degradation, nitrogen conservation, compost stability, and HS formation. The review also discusses maturity and quality indicators, including the humification index, E4/E6 ratio, germination index, and leachate management, together with the role of vermicomposting and cascade biorefinery approaches in maximizing resource recovery. Current evidence indicates that residual avocado biomass constitutes a promising feedstock for producing stable humified organic amendments while contributing to nutrient recycling, soil fertility, carbon sequestration, and circular bioeconomy strategies. Finally, major research gaps are identified, particularly regarding avocado-specific biodegradation kinetics, integrated process monitoring, predictive modeling, and intelligent process-control systems, providing future directions for the optimization and industrial implementation of composting technologies for sustainable agro-industrial waste valorization.