Comparison of Reactor Configurations for Biogas Production from Energy Crops

Biogas production from a mix of easily fermentable and fibrous energy crops was evaluated and compared for two different process types. The processes were a batch two-stage leach bed combined with an upflow anaerobic sludge blanket (UASB) process and a semi-continuous one-stage continuously stirred tank reactor (CSTR) process The specific methane yields after a processing time of 29-30 days were 248 and 370 ml methane g
^-1
added volatile solids (VSadded) in the leach bedUASB and the CSTR processes respectively. The average VSremoval rate of the leach bed-UASB system was initially faster, but when that process became limited by solids hydrolysis, the VS-removal rate dropped to less than half the initial rate, and the overall degradation was slower than for the CSTR. In conclusion, the biogas production was influenced significantly by the reactor configuration, but the effect of crop particle size and the influence of inoculum and microbial adaptation remain to be investigated.