Association of pre-treatments and anaerobic digestion aiming energy valorization of the main residues in the coffee production chain

Abstract

Brazil is the world leader in the production and export of coffee. The country is also the largest producer and exporter of instant coffee. The production of instant coffee generates large quantities of liquid and solid by-products, among which, the effluent from the extraction process and the coffee spent grounds stand out. Anaerobic digestion can mitigate the environmental impact caused by the incorrect disposal of these residues. The adequate use of this technology can also contribute to the energy sustainability of the instant coffee production chain, and to the diversification of the Brazilian energy matrix. The composition of these residues, however, brings difficulties to its anaerobic digestion due to the presence of lignin and other phenolic compounds. Thus, the present project aims to study chemical (acidic and basic) and hydrothermal pretreatments applied to coffee spent grounds and fungal pretreatment (Pleurotus ostreatus) applied to instant coffe effluents to decrease their recalcitrance and toxicity, facilitating its anaerobic digestion. Initially, the residues will be physicochemically characterized and its biomethane potential determined. The kinetic parameters of the residues will be then estimated and the mathematical modeling of the processes will be performed. The estimation of kinetic parameters will be carried out in reactors operated in sequential batches submitted to an initial concentration of increasing organic matter so that the optimal conditions for methanogenic production and organic acids are evidenced. The organic acids formation is expected under overload conditions. After the characterization, the study of the influence of the pre-treatments will be carried out. Auto-hydrolysis and physical-chemical pre-treatments will be applied to the spent coffee grounds. The alkaline treatment will be studied aiming at the removal of lignin from the residue, and later, the acid and hydrothermal treatments will be carried out aiming at the removal of the hemicellulosic fraction. The acidic treatment of the spent coffee grounds will be carried out using of coffee processing effluent that has a low pH value, replacing the addition of chemicals. The efficiency of the pre-treatments will be verified through the study of the methanogenic production from the degradation of the treated solid fractions and the produced hydrolysates. The alkaline liquor generated in the alkaline pretreatment of the coffee grounds will be codigested with the acid effluent from the coffee processing. The fungal pretreatment will be applied to the effluent from the production of instant coffee in order to promote the reduction of soluble lignin and total phenolic compounds. This stage of the project will be carried out with the aid of in silico studies of molecular docking and factorial experimental planning to verify conditions that cause higher rates of fungal growth and laccase production. Effluents with and without pretreatment will be subjected to anaerobic digestion so that the biomethane potential evaluated. This project will be carried out in the Laboratory of Environmental Biotechnology of FZEA / USP and will count on the partnership of researchers from Federal University of Campina Grande (Prof. Glauciane Coelho's group) in the study of fungal pretreatments. It is expected to contribute to the area of degradation of recalcitrant compounds, generation of bioenergy and products of interest from three of the main residues of the coffee production chain. In this way, it is intended to foster the creation of a biorefinery coupled with the instant coffee production chain with the potential to produce enzymes, organic acids and bioenergy. In addition to the training of three masters, one doctor and a under graduation student, the results of the project now presented will subsidize the submission of a patent application related to the fungal pretreatment of the liquid effluent of soluble coffee and the publication of 7 manuscripts. (AU)