Study of Valorisation Routes of Spent Coffee Grounds

Purpose The energy crisis is an eminent problem that needs to be dealt with urgently. Thus, alternative routes for the production of biofuels are sought. This paper investigated experimentally the possibility of biodiesel and bioethanol production from spent coffee grounds (SCG), aiming at the same time to manage an emerging waste stream. Methods SCG have oil and cellulose contents of 12.89% and 9.87%, respectively that may be valorized accordingly. Having chosen the Soxhlet method as an extraction method for oils and fats and by examining two different solvents: methanol as a polar compound and hexane as a nonpolar, the effect of the Soxhlet extraction cycles (time of experiment) and the ratio of solvent to raw material was studied. Furthermore, enzymatic saccharification and alcoholic fermentation were chosen as the means to valorise cellulose. Results It was proved that hexane is a more efficient solvent with oil extraction yields ranging from 73.15 to 97.21%. The highest yield was obtained for 20 extraction cycles and solvent to raw material ratio equal to 20. As far as enzymatic hydrolysis is concerned, the maximum saccharification yield for SCG was 44.20% which was achieved under the following conditions: NaOH 0.3 M and CellicCTec2 75 mu L/g cellulose. Conclusion It is thus technically feasible to recover and extract the oil content from spent coffee grounds as well as to achieve moderate saccharification yields and to this direction an integrated biorefinery was proposed. Estimating the potential of SCG as feedstock for biodiesel and bioethanol production at global level, it was evident that SCG can contribute to the energy strategy through biofuels promotion. [GRAPHICS] .