Bacterial and archaeal community structure involved in biofuels production using hydrothermal- and enzymatic-pretreated sugarcane bagasse for an improvement in hydrogen and methane production
Sugarcane bagasse (SCB) was used as a lignocellulosic substrate, combining the co-production of H2 (Stage I) and CH4 (Stage II) by a dark fermentation process in batch reactors. Hydrothermally- and enzymatic (Aspergillus niger)-pretreated SCB were applied as substrate sources. Two fermentative inocula (In1 and In2) were used in Stage I and a methanogenic inoculum in Stage II (In3), comprising in total three experimental series in relation to Stage I: A (In1), B (In1 plus In2), and C (In2). The final metabolites (solid, liquid, and gaseous fractions) from Stage I were used for CH4 production (Stage II). The SCB pretreatment employed was favorable for biogas and organic acids production. Higher H2 and CH4 yields were obtained in C (4.3 and 6.3 mmol g−1 SCB, respectively). For all conditions, the H2 production occurred primarily via an acetic acid route. The predominance of cellulolytic enzyme producers (Enterococcus and Clostridium) may have favored the H2 and subsequent CH4 production; this last was produced mainly from members of the Methanoregulaceae and Methanosaetaceae families. Furthermore, homoacetogenic bacteria (Acetobacterium, Clostridium, Eubacterium, Holophaga) were also identified in both stages. The synergistic action of these microbial groups promoted the hydrolysis of SCB as well as hydrogen and methane production.