Anaerobic Digestion of Liquid Fraction Coffee Grounds at Laboratory Scale: Evaluation of the Biogas Yield

Abstract

Abstract Coffee is one of the most popular beverage in the world. The International Coffee Organization (ICO) in the last 4 years registered an average world consumption higher than 8x106 tons. Over 50% of this mass is discarded after use, becoming a significant waste source known as spent coffee grounds (SCG). SCG usage as a raw material for biogas production emerges with great potential. It is a biomass that does not need pre-treatment, rich in lipids and can be easily separated in bars and restaurants. Lipid concentrations in SCG can reach more than 25% of its dry weight and 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. Airtight glass reactors have been realized to guarantee the anaerobic digestion conditions. The reactors, divided into two groups A and B, fed with SGC and cow manure respectively, have been monitored for 22 days at a temperature of 37 °C. The accumulated methane production for a total of 1444 ml of biogas for group A and 1047 ml of methane for Group B was observed. Group A had an output of 296 ml.CH4/g-VS and group B 312 ml.CH4/g-VS. Group A presented fractions of 53.7% of CH4 and 37.80% of CO2. The B group showed 36.7% of CH4 and 27.9% of CO2. In the Group A, the methane production from SGC, reached concentration higher than 50%. This result shows the SCG liquid fraction energy recovery potential using an anaerobic digestion process.