The effect of aqueous ammonia soaking pretreatment on methane generation uing different lignocellulosic feedstocks

Lignocellulosic biomass including agricultural and forestry residues, perennial crops, softwoods and hardwoods, can be used as feedstock for methane production. Although being abundant and almost zero cost feedstocks, the main obstacles of their use are the low efficiencies and yields attained, due to the recalcitrant nature of their lignocellulosic content. However, with the application of a pretreatment process, depolymerization of cellulose and hemicellulose and breaking the lignin seal can be achieved facilitating the liberation and subsequent uptake of simple sugars (hexoses and pentoses), that can be converted to methane in consecutive steps, by microorganisms, , leading thus to higher yields.
Among different pretreatment technologies, aqueous ammonia soaking (AAS) presents certain advantages since ammonia is relative safe to handle, non polluting, non corrosive, easily recoverable and presents a high selectivity toward the lignin reactions, preserving the carbohydrates [1]. AAS is a novel and promising pretreatment in the anaerobic digestion field. Switch grass [2], wheat straw, willow and miscanthus [3] and manure fiber [4] are the lignocellulosic feedstocks which have been pretreated with AAS for enhanced methane production, so far.
In the present study AAS has been tested as a pretreatment method in anaerobic digestion of three lignocellulosic feedstocks with a different origin: one agricultural residue: sunflower straw, one perennial crop: grass and a hardwood: poplar. The effect of the AAS pretreatment on methane yield and on the structural characteristics of the feedstocks was assessed. A detailed characterization of the pretreated feedstocks through techniques such as scanning electron microscopy (SEM), X-Ray diffraction (XRD) and IR spectroscopy will also be presented.

References
[1] Kim, M., Aita G, Day DF.: Compositional changes in sugarcane bagasse on low temperature, long-term diluted ammonia treatment, Appl Biochem Biotechnol. 161, 34–40 (2010)
[2] Himmelsbach, J., Raman, D., Anex, R., Burns, R., Faulhaber, C. :Effect of ammonia soaking pretreatment and enzyme addition on biochemical methane potential of switchgrass. Transactions of the ASABE. 53, 1921-1927 (2010)
[3] Jurado, E., Gavala., H.N., Skiadas, I.V., :Enhancement of methane yield from wheat straw, miscanthus and willow using aqueous ammonia soaking. Environmental Tecnology. 34(13-14), 2069-2075 (2013)