Anaerobic digestion of coffee grounds soluble fraction at laboratory scale: Evaluation of the biomethane potential

The biochemical conversion of residual biomass may give a significant contribution to the flexible and programmable production of renewable electric and thermal power. In this perspective the use of residuals from coffee chain, which is one of the most popular beverage in the world, is of utmost importance due to the large quantity produced. Over 90% of this mass is discarded after use, becoming a significant waste source known as spent coffee grounds SCG. SCG use as a raw material for biogas production emerges with great potential. SCG is a biomass that does not need pre-treatment, rich in lipids which can be easily recovered in bars and restaurants where it is properly separated. Lipids, which concentrations in SCG can reach more than 25% of its dry weight, have a good biogas production behavior, producing over 1 liter of CH4/g-VS. In this paper, the analysis of biogas yield potential of SCG recovery is presented using a laboratory scale batch anaerobic reactor, fed with the liquid fraction obtained by spent coffee filtration. The use of SCG liquid fraction in conjunction with cow manure has been monitored for 22 days at a temperature of 37 °C showing a specific SCG production contribution up to 254 ml CH4/gVS. An increase of ≅ 10% in the methane fraction in Biogas production has been observed with an average LHV of about 28.24 MJ/kg. This result shows the SCG liquid fraction energy recovery potential using an anaerobic digestion process.