Abstract
Effects of a crush process on methane conversion efficiency in thermophilic anaerobic digestion with coffee grounds were evaluated. The crush process was performed with a blender (10,000 rpm). In batch experiments, solubilization rates for crushed coffee grounds (representative particle size: 320 μm) were greater than 8.10% at 55°C for 24 h, and the rate for uncrushed grounds (> 1,000 μm) was 5.00% under the same conditions. In a batch experiment, methane conversion efficiency for crushed grounds (45.4%) was higher than that for uncrushed grounds (27.7%) in the thermophilic anaerobic digestion process (120 h). The contribution of acetic acid to the conversion efficiency was suggested. Continuous experiments (solubilization and thermophilic anaerobic digestion) were conducted with loading rates of 5 and 6.5 kg COD/m3/day. The experiments also showed average efficiencies for the crushed samples (41.1% and 39.3%, 5 and 6.5 kg COD/m3/day, respectively) were higher than uncrushed samples (33.4% and 32.4%). Moreover, the crushing process improved the total solid decomposition. Based on these results, it was found that anaerobic digestion using a crush process is effective, especially for coffee grounds with a representative particle size of 320 μm.
