Effects of Substrate Loading Rate in Anaerobic Co-digestion of Cow Manure and Energy Crops

The feasibility of the anaerobic co-digestion of cow manure (CM) and energy crops (EC) was investi- gated in both batch and continuous experiments. A positive synergistic effect (about 8 %) for methane yield was observed by co-digesting CM and EC in batch experiments. Completely-mixed reactors for mono-digestion of CM and co-digestion of CM and EC (either dent corn or rice straw) were semi-continuously operated at a constant influent VS level of 10 %. The VS mixing ratio was set at 1 : 0 . 5 (EC/CM) in co-digestion. Stable and efficient co-digestion at hydraulic retention times (HRTs) of 30 days (mono-digestion basis) were obtained. Methane production increased by 61 % and 45 % in the dent corn co-digestion and the rice straw co-digestion, respectively, co mpared with the mono-digestion. At HRTs of 22 . 5 days (mono-digestion basis), the performance of co-digestion was also stable. Methane production increased by 57-72 % in the co-digestion reactors compared with mono-digestion. The results suggested that EC can be used as a co-substrate of CM anaerobic digestion for a significant methane production increase.