Hydrothermal and chemical pre-treatments of wastes from the soluble coffee production coupled to metanogenesis

Abstract

The anaerobic digestion of lignocellulosic residues from industrial processes applied to the generation of methane has the potential to assign energy value to avaiable materials that have costly treatment and disposal. The use of residual biomass contributes to the diversification of the energy base without increasing competition for arable land between monocultures aiming production of biofuel and cultures aiming food production. Among the lignocellulosic residues, there are those generated in extraction processes, such as coffee grounds. About 50% of all haversted coffee beans are used to produce instant coffee by vaporization. Such process of extracting flavorings from the coffee bean results in a solid residue with a high lignin content. Due to the recalcitrance of the lignocellulosic residue, the anaerobic digestion of coffee grounds depends on pre-treatments prior to the biological process. Then, the present project proposes the sequential combination between the alkaline and hydrothermal pretreatments and between the alkaline and acid pretreatments of the coffee grounds. Both combinations intend the removal of lignin by the alkaline treatment done prior to the removal of the hemicellulosic fraction by hydrothermal and acid pretreatments. The first combination allows to analyze the influence of the lignin content on the efficiency of the hydrothermal pre-treatment in the production of less toxic hydrolyzate and less recalcitrant solid fraction. The second combination allows the acid effluent from the coffee industry to be studied in the treatment of coffee grounds without the need to add chemicals for the production of less recalcitrant solid fraction for different levels of lignin in the coffee grounds. The efficiency of the pre-treatments will be related to the methanogenic production resulting from the anaerobic digestion of the treated solid fractions and the hydrolyzates and also from the anaerobic codigestion between the alkaline liquor and the coffee processing effluent. (AU)