A Feasible Application of Circular Economy: Spent Grain Energy Recovery in the Beer Industry

Abstract

Energy recovery from wastes is needed for cost-effective and sustainable management. For a given waste, the definition of suitable thermochemical conversion process schemes relies on devising a strategy based on several variables among which feedstock characterization is crucial. Depending on the properties of the fuel, the available waste resource may not be suitable for a specific application, for technical and sometimes for environmental reasons (Virmond et al. in Braz J Chem Eng 30:197–230, 2013). Within this framework, agro-industrial wastes (grape stem, beer bagasse and orange juice residues) were characterized and the results are used to design a strategy for their effective integration in waste-to-energy processes. Energy content, proximate and ultimate analysis, composition, ash fusibility and thermal behaviour were determined. For the physicochemical analysis UNE standard methods were used. Characterization results showed that the three wastes have good quality for thermochemical conversion with energy contents between 19 MJ/kg (beer bagasse) and 16 MJ/kg (orange juice residue) and ash contents below 10% in all cases. However, some drawbacks were found: high moisture (76%), nitrogen (3.5%) and sulphur (0.2%) content for beer bagasse; elevated nitrogen (1.1%) and sulphur (0.15%) concentration for grape stem and nitrogen (1%) content for orange juice residue. All this information has been used to design a smart strategy for selecting a sustainable and environmental friendly waste to energy processes as part of a circular economy approach.