Improving biogas yields using an innovative pretreatment concept for conversion of the fiber fraction of manure

A new concept to enable economically feasible operation of manure based biogas plants was tested in lab-scale. Wet explosion (WEx) was implemented as treatment of the residual manure fibers separated after the anaerobic digestion process for enhancing the biogas production before reintroducing into the biogas reactor. The increase in methane yield of the digested manure fibers was investigated by applying the WEx treatment under 5 different process conditions. The WEx treatment at 180 ºC and a retention time of 10 minutes without addition of oxygen was found to be optimal, resulting in 136% increase in methane yield compared to the untreated digested manure fibers in batch experiments. In a continuous mesophilic reactor process the addition of WEx treated digested fibers in co-digestion with filtered manure did not show any signs of process inhibition and the overall methane yield was in average 75% higher than in a control reactor with addition of non-treated digested fibers.