Resumo

Hydrogen (H2) is a promising alternative to fossil fuels due to its clean and high-energy yield. Cellulose is the most abundant renewable natural resource in the world and may be applied as an economical source for the H2 production. This study aimed to evaluate the production of H2 from leachate in mesophilic conditions, using cellulose as substrate in the presence and absence of the enzyme cellulase. Previously, leachate was subjected to heat-shock treatment and the biomass was enriched in the modified Del Nery medium with cellulose. Assays for the hydrogen production were carried out using 2.5 g/L and 5.0 g/L of celullose, in the presence and absence of cellulase. The H2 yield was 1.2 mol H2/mol hexose and 0.6 mol H2/mol hexose in reactors with 2.5 and 5.0 g/L cellulose plus cellulase, respectively. The cellulose consumption was lower in reactors fed with 5.0 g/L of cellulose (28.4%) compared with the reactors fed with 2.5 g/L of cellulose (41.4%). The low H2 yield obtained in the reactor fed with 5 g/L cellulose can be associated with a lack of carbohydrate readily available by microorganisms. Hydrogen gas production was associated with the formation of acetic, butyric, iso-butyric and propionic acids in reactors with cellulase. Hydrogen production was not detected in the reactors that did not receive cellulase. Microscopic analysis showed the predominance of gram-positive rods with endospore, characteristic of microorganisms which produce H2. PCR/DGGE analysis showed differences in microbial community structure between the reactors, which probably reflect the diverse conditions, imposed, such as heat-shock, presence of cellulase and substrate concentration. After sequencing and BLAST analysis it was identified two class Clostridia and Gammaproteobacteria, which are part of a hydrogen production genus, such as Clostridium sp. and Enterobacter. The H2 production was observed only in reactors with cellulase, highlighting the importance of this enzyme for the hydrolysis of cellulose into soluble sugars.