Biorefinery potential of coffee silverskin: Composition and applications

Purpose: Achievements in biotechnology have paved the way for the efficient utilization of agricultural and industrial waste, presenting potential opportunities for sustainability and resource optimization. One such waste that has been studied is coffee silverskin (CS), the only waste generated during the coffee roasting process. This paper aims to analyze the potential of CS for biorefinery and explore its value enhancement through biotechnology. Method: The study employed various analytical techniques, including elemental analysis, chromatography methods, and Fourier transform methods, to characterize the CS biomass. Additionally, three formulations for wet granulations of a biofertilizer were prepared to valorize the silverskin. Empirical formulas were used to assess the fatty acid content and key parameters of CS biodiesel precursor. Results: The results revealed that CS, when enriched with microalgae and bindered with glauconite, becomes high-value amendment rich in essential macro- and micronutrients. The optimal biofertilizer composition suggested a ratio of three parts of CS, one part of glauconite, and 5 parts of the Chlorella vulgaris microalgae suspension with the liquid-to-solid ratio of 1.28. The higher heating value, the cetane number, the iodine value, the viscosity, and the density of precursors obtained comply with the requirements of the standard EN 14214. Conclusion: The CS was found to contain significant amounts of palmitic and linoleic acid, which are known to be value-added components in cosmetic formulations and biodiesel production. The high macro and micro-nutrient contents of CS, make it an attractive opportunity to adopt a circular bioeconomy model in the agricultural sector. By transforming organic waste, the coffee roasting industry can achieve the goal of Zero Waste, contributing to a more sustainable and environmentally friendly approach.   Highlights Pelleted biofertilizer not reported before has beneficial agronomic properties Optimal biofertilizer composition: CS : glauconite : Chlorella vulgaris suspension (3:1:5) Optimum liquid-to-solid ratio for pellet agglomeration during control process is 1.28 CS biodiesel precursor has good ignition characteristics with a cetane number of 62 Data gaps on the lignin and carbohydrate content in CS have been filled