Study of the thermo-oxidative decomposition of beer production residues for their use in valorisation processes

The accumulation of huge amounts of food wastes every year has led to environmental degradation and especially to significant loss of valuable material. Steady consumption of beer results in a steady output of residues. Brewer’s spent grain (BSG) is the most abundant by-product generated in the beer-brewing process. BSG consists of the barley grain husks together with parts of the pericarp and seed coat layer that is obtained as solid residue after the production of beer wort. Despite the wide range of possible applications, its main use is limited to animal feed or simply deposition to landfills. The study of alternative uses of BSG is appropriate, both from the perspective of the brewer who can benefit from the valorisation but also from an environmental outlook. However, a significant understanding gap regarding the variability of this low-cost residue, its influence in the valorisation process and its use in biorefineries exists. This study attempts to characterize two different types of BSGs and the malts by which they are composed in terms of elemental composition, higher heating value, content of volatiles, fixed carbon, humidity, ash yield and to study the kinetic mechanism of decomposition during thermo-oxidative combustion. In terms of methodology, proximate analysis, ultimate analysis and calorific values were performed, as like as thermogravimetric analysis. Thermogravimetric thermograms were determined at different heating rates, using oxygen as oxidative atmosphere. The thermo-chemical reactions were mathematically described through the definition of the main kinetic parameters: activation energy, pre-exponential factor, model of reaction. The so-called kinetic triplet was calculated through the application of iso-conversional methods, Master-Curves and Perez-Maqueda criterion. The results of this study will serve as the baseline for the description of the energy recovery process in a reactor that uses brewer’s spent grain residues as feedstock.