Anaerobic mesophilic batch tests of energy crops (forage barley, rye, Italian ryegrass, and oats) were carried out to evaluate their ultimate biodegradability and two distinctive decay rates (k1 and k2) with their corresponding degradable substrate fractions (S1 and S2). Graphical statistical analysis and biochemical methane potential (BMP) tests showed that the ultimate biodegradability was 82 ~ 88% for forage barley, 70 ~ 77% for rye, 66 ~ 79% for Italian ryegrass, and 59 ~ 67% for oats. The readily biodegradable fraction (S1) of 73% of forage barley biodegradable volatile solid (BVS, S0) degraded within the initial 40 days at k1 of 0.055 day−1, whereas the slowly biodegradable fraction (S2) of BVS degraded over more than 80 days with long term batch reaction rates of 0.002 day−1. For oats, this readily biodegradable portion (S1) was 57%, which degraded with a k1 of 0.023 day−1 for the initial 60 days. The minimum hydraulic retention time (HRT) for the anaerobic digestion of forage barley, rye, and Italian ryegrass were estimated in the range 45 ~ 55 days and 65 days for oats.

Anaerobic mesophilic batch tests of dairy cow manure, dairy cow manure/saw dust mixture and dairy cow manure/ rice hull mixtures collected from bedded pack barn were carried out to evaluate their ultimate biodegradability and two distinctive decay rates (k1 and k2) with their corresponding degradable substrate fractions (S1 and S2). Each 3 liter batch reactor was operated for more than 100 days at substrate to inoculum ratio (S/I) of 1.0 as an initial total volatile solids (TVS) mass basis. Ultimate biodegradabilities of 37 ~ 46% for dairy cow manure, 32 ~ 40% for dairy manure/saw dust mixture and 31 ~ 38% for dairy cow manure/rice hull mixture were obtained respectively. The readily biodegradable fraction of 90% (S1) of dairy manure BVS (So) degraded with in the initial 29 days with arange of k1 of 0.074 day−1, where as the rest slowly biodegradable fraction (S2) of BVS degraded for more than 100 days with the long term batch reaction rate of 0.004 day−1. For the dairy manure/saw dust mixture and dairy manure/rice hull mixture, their readily biodegradable portions (S1) appeared 71% and 76%, which degrades with k1 of 0.053 day−1 and 0.047 day−1 for an initial 30 days and 38 days, respectively. Their corresponding long term batch reaction rates were 0.03 day−1.