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Industrial development and increased energy requirements have led to high consumption of fossil fuels. Thus, environmental pollution has become a profound problem. Every year, a large amount of agro-industrial, municipal and forest residues are treated as waste, but they can be recovered and used to produce thermal and electrical energy through biological or thermochemical conversion processes. Among the main types of agro-industrial waste, soluble coffee residues represent a significant quantity all over the world. Silver skin and spent coffee grounds (SCG) are the main residues of the coffee industry. The many organic compounds contained in coffee residues suggest that their recovery and use could be very beneficial. Indeed, thanks to their composition, they can be used in the production of biodiesel, as a source of sugar, as a precursor for the creation of active carbon or as a sorbent for the removal of metals. After a careful evaluation of the possible uses of coffee grounds, the aim of this research was to show a broad characterization of coffee waste for energy purposes through physical and chemical analyses that highlight the most significant quality indexes, the interactions between them and the quantification of their importance. Results identify important tools for the qualification and quantification of the effects of coffee waste properties on energy production processes. They show that (SCG) are an excellent raw material as biomass, with excellent values in terms of calorific value and low ash content, allowing the production of 98% coffee pellets that are highly suitable for use in thermal conversion systems. Combustion tests were also carried out in an 80kWth boiler and the resulting emissions without any type of abatement filter were characterized.

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Autothermal gasification of lignin-rich residues was carried out to evaluate the performances of a pilot plant with a feeding rate of 20−30 kg h −1 of feedstock. The facility was based on an updraft gasifier and a gas cleaning train composed of a biodiesel scrubber and coalescence filters. The tests were performed with solid residues of ethanol production starting from straws or canes. Air at a low equivalence ratio was used as gasification medium. The autothermal processing and the lignin-rich feedstock made it possible to highlight a sequence of exothermic and endothermic reactions by measuring the heating rates along the reactive bed. The CO 2 production was proportional to the ash content. The average production of raw syngas was 1.94 kg per kg of dry residue, of which H 2 and CO were 27.2 and 696 g, respectively. The efficiency of energy conversion from solid to cold gas was 64% and reached about 81% including the contribution of the condensable organic fraction.

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