The Effect of Aqueous Ammonia Soaking Pretreatment on Methane Generation Using Different Lignocellulosic Biomasses

Abstract

In the present study aqueous ammonia soaking (AAS) has been tested as a pretreatment method for the anaerobic digestion of three lignocellulosic biomasses of different origin: one agricultural residue: sunflower straw, one perennial crop: grass and a hardwood: poplar sawdust. The methane production yield was evaluated in batch experiments at different organic loadings, in order to assess any inhibitory effects due to the pretreatment. The experiments showed that the increase of organic loading did not affect the final methane yield of either raw or AAS pretreated biomasses. Among the three biomasses tested, poplar sawdust exhibited the lowest methane yield, due to its high lignin content. AAS treatment led to an increase of the ultimate methane yields of all biomasses, with the increase in the case of poplar, sunflower straw and grass being 148.7, 37.7 and 26.2 %, respectively. AAS resulted in solubilization of hemicellulose and partial removal of cellulose for all biomasses. Higher cellulose degradation was observed in grass biomass, in which a different morphology than the other AAS treated samples, was shown in SEM images. No toxic compounds such as furaldehydes, were produced during AAS pretreatment.