Anaerobic digestion of post hydrothermal liquefaction wastewater of spent coffee grounds

Abstract

The project aims the structuring of an energy balance of the process that includes the production of bio-oil by hydrothermal liquefaction of the spent coffee grounds and biogas recovery from the study of anaerobic biodegradability of the effluent resulting from this emerging physicochemical process. The system proposes the waste recovery by using it in the biofuels production to meet growing energy demand and dissociate the focus from the use of fossil fuels. The hydrothermal liquefaction process will be conducted by means of an association between the high moisture solid fraction, spent coffee grounds, residue of the soluble coffee production process, and water in a 1:20 ratio, at a temperature of 275oC and detention time of 10 minutes. After the hydrothermal liquefaction reaction, a characterization stage of the effluent will be conducted.After the characterization, anaerobic biodegradability of the effluent and adaptation of anaerobic sludge will begin. The sludge will be applied in initial COD tests varying in 0.5, 3.5; 5; 7.5; 10; 15 and 30 gO2.L-1, in order to determine the biogas production and the kinetic parameters of the anaerobic digestion of the effluent. The tests shall be performed in 120 ml flasks operated in batches and submitted to the N2 atmosphere at a temperature of 37°C under a rotation of 150 rpm. Once the kinetic constants have been determined, batch assays will be carried out in order to determine intermediate compounds of the digestion. Once determined the volatile acids, a mathematical modeling will be performed according to the study and understanding of Anaerobic Digestion Model No 01 (ADM1). This study will provide parameters that potentially allow theunderstanding of the effluent digestion and positively contribute to the energy matrix of the spent coffee grounds thermo-chemical conversion process.