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.