Enhanced methane productivity from swine manure fibers by aqueous ammonia soaking pretreatment

The necessity of increasing the methane productivity of manure based biogas plants has triggered the development of new separation technologies for being applied before anaerobic digestion of the manure. Thus, manure solid and liquid fractions could be used to centralized biogas plants for methane production and as fertilizer on the farm, respectively. One of the challenges of this approach is that the solid fraction of manure contains lignocellulosic fibers, which are difficult to digest and thus make anaerobic digestion process slow and economically unfavourable. In the present study, aqueous ammonia soaking (AAS) was investigated as a pretreatment method to disrupt lignocellulosic structure and increase methane potential of swine manure fibers. It was proven that AAS broke down the lignocellulosic structure dissolving approximately the 35% of lignin and maintaining cellulose and hemicelluloses almost intact. Subsequent enzymatic hydrolysis with 15 FPU per g of TS for four days released almost 94% of glucose and 91% of xylose found in manure fibers. AAS pretreatment exhibited a significant effect on methane production rate and potential. It was found that AAS for 3 days at room temperature were the optimal conditions among the ones tested, resulting at a 78% increase in methane yield from manure fibers. AAS at 55°C did not exhibit any extra benefit for methane production compared to room temperature.