Resumo

There is great interest in the use of cellulosic biomass as a renewable source of energy. Biological production of hydrogen (H2) by using biomass has been attracting attention as an environmentally friendly process that does not consume fossil fuels and it is a clean energy resource. H2 production by microbial consortium enriched from leachate was studied by using Del Nery medium with 10 g/L of cellulose, in the presence and absence of cellulase. Heat-shock treatment was applied to select H2-producing bacteria and favored a predominance of Gram-positive rods and endospore-forming bacteria, relevant characteristics of hydrogen producers microorganisms. The H2 yield was 2.3 mol H2/mol hexose and the cellulose consumption was 44.7%. In reactor fed with cellulase diverse acids were produced (acetic, iso-butyric and propionic acids) with a predominance of butyric acid. The pH values decreased from around 7.0 to 3.5 and then H2 production stopped. These results were expected since hydrogen evolution by Clostridium sp. proceeds at neutral pH, but are inhibited in the pH range 4-5. In control reactors without cellulase, H2 production was not observed and the final pH was 5.6. This result shows that absence of cellulase inhibits the H2 production by microorganisms. Based on the phylogenetic analysis of the rDNA sequences, all the clones evaluated (100%) had similarity with Clostridiaceae family. Clone 1 showed 99% of similarity with C. acetobutylicum and the 86 clones remaining were related to Clostridium sp. Conditions imposed in the present assay favored the selection of microorganisms of the genus Clostridium, recognized in the literature as generator of H2. The heat shock applied to the leachate was effective to inhibit methanogenic archaea, because methane was not detected at conditions studied, however, this pre-treatment may have caused the inhibition of cellulolytic bacteria present in the leachate. The addition of cellulase was essential to promote cellulose hydrolysis into soluble carbohydrates, which allowed hydrogen production by bacteria present in the consortium. Biohydrogen production was basically via butyric acid, the principal by-product generated.