Digestibility of Riverbed Plants by Dry-Thermophilic Anaerobic Digestion

The dry-thermophilic anaerobic digestibility of alternative biomasses to rice straw for pig manure treatment was evaluated. Seven grass and three woody biomasses were subjected to batch dry-thermophilic anaerobic digestion for methane (CH4) production. The CH4 production potential ranged from 109 +/- 8.1 to 347 +/- 62 m(3)/t-VS, with woody biomasses showing the lowest potential. This trend indicates a negative correlation between lignin content and CH4 production potential, suggesting that lignin content determines the CH4 production of the grass and woody biomasses. CH4 production quantities in Ibaraki Prefecture, where pig farming has been intensively practiced, were estimated to be respectively 31.3, 1.68, and 1.42 m(3)/y from rice straw, riverbed grasses, and wood (from riverbeds, parks, roads, and orchards). CH4 production yields from semi-batch dry-thermophilic anaerobic digestion of pig manure with cogon grass (Imperata cylindrica) and wood chips were respectively 251 +/- 44 and 157 +/- 9.4 m(3)/t-VS. These values were comparable to the CH4 production potential of these biomasses, suggesting their promise as alternatives to rice straw.