Thermochemical and biochemical conversion technologies for the valorization of coffee-industry residues: a systematic review

Introduction The accumulation of agro-industrial residues in the coffee sector poses environmental and logistical challenges. This systematic review analyzes thermochemical and biochemical conversion technologies for the valorization of these streams. Methods Following the PRISMA 2020 guidelines and the PICO strategy, 116 primary studies published between 2020 and 2025 and indexed in Scopus and Web of Science were selected. Results Thermochemical routes, with a focus on slow pyrolysis, and biochemical pathways, such as anaerobic digestion and composting, represent the dominant recovery configurations. These systems recover biogas, biochar, biofertilizers, and liquid biofuels. Quantitative data indicate that an integrated combined cooling, heating, and power system using spent coffee grounds decreases global warming potential by 37.6% compared to a baseline scenario, using 1 kg of instant coffee as the functional unit. Furthermore, decentralized pyrolysis configurations on farms decrease thermal drying energy costs by 20% to 35% through the replacement of subsidized fossil fuels with local biochar. Discussion Operational limits include feedstock heterogeneity, implementation costs, low technology adoption in rural sectors, and a lack of biofertilizer regulations. Integrated biorefineries represent a pathway to standardize processes and establish commercial-scale operations.