Anaerobic codigestion of cow slurry with grass silage: Effect of silage duration

The anaerobic codigestion of cow slurry with roadside grass was investigated in this study. Ensilage is known to enhance the anaerobic digestibility of grass, but the literature does not provide accurate information about the suitable silage duration needed to ensure effective codigestion. Grass was cut along roadsides and ensiled for different durations without additives. Anaerobic digestion batch tests were carried out by mixing cow slurry and grass silage. The following three silage durations were tested: 3, 8 and 36 weeks. Each mixture was tested twice and no additional inoculum was used. Compared with their respective controls (slurry only), methane yield (L-CH4/kgVS(added)) decreased by 14% and 5% for the 3 and 8 week silage tests, respectively, and increased by 15% for the 36 week grass silage test. The 8 week grass silage, which showed a slight decrease of 5% at the end, did not inhibit the process. Thus, we conclude that it is more appropriate to use a grass with a minimum silage duration of 8 weeks as a cosubstrate. (c) 2016 American Institute of Chemical Engineers Environ Prog, 35: 1374-1380, 2016