DISCUSSION OF POSSIBLE COFFEE GROUNDS DISPOSAL CHAINS FOR ENERGY PRODUCTION

The average Italian person consumes 5.9 kg of coffee every year. Most of this coffee is brewed in bars where the spent powder is disposed in the garbage bin togheter with other wastes. This work puts the focus on the potential of spent coffee grounds as energy resource. The powder collected from bar is in major part water. This is caused by the brewing process but, after drying it up it is possible to characterize the spent powder. The first analyses were followed by a combustion test on a 8 kW pellet stove run with pellet obtained directly from spent coffee grounds. The pellet fuel passed the test even if some issue where reported. In order to increase the performance of the pellets, together with the increase of the value of the feedstock, part of the coffee grounds were processed in a Soxhlet cycle with isopropyl alcohol in order to separate the residual oil content from the solid powder. After the washing process, the oil was recovered through distillation. Results showed a fraction of about 7.2% wt. of oil in spent dried coffee grounds. The oil resulted comparable to heavy fuel oils. In addition, treated dried spent coffee grounds present characteristics similar to wood pellets in terms of higher heating value and atomic H/C and O/C ratios.