Polyphenols and energy recovery from spent coffee grounds

Spent coffee grounds were investigated as a potential source of high-value phenolics and energy. Phenolic extraction was performed by the use of 60% (v/v) ethanol in water as the solvent. Under the best conditions (temperature = 60 degrees C; extraction time = 180 min; liquid-to-solid ratio = 50 mL/g) over 1500 mg of phenolics per 100 g of dry coffee grounds were obtained. Calorimetric measurements showed that coffee grounds had a high calorific value (about 24 MJ/kg) and that this property did not change on extraction of phenolic compounds. Overall, these results suggest that phenolic-rich extracts can be obtained from spent coffee grounds using a low-cost, environmentally benign and non-toxic extraction procedure and that the resulting solid residue can be further exploited for energy production.