Combined heterogeneous catalysis and dark fermentation systems for the conversion of cellulose into biohydrogen

•Cellulose was converted to hydrogen by heterogeneous catalysis and dark fermentation.•The WSF from cellulose hydrolysis was further bioprocessed without any pretreatment.•Citrobacter and Enterobacter fermented the WSF producing H2 and other metabolites.•The highest H2 yield in the dark fermentation was for Enterobacter and Citrobacter.

A two-step combined system consisting of heterogeneous catalysis followed by dark fermentation was investigated for the production of biohydrogen. Cellulose in the aqueous phase was hydrolysed in an autoclave reactor with ZrO2 catalysts modulated by three different promoters: sulfate, fluoride, and phosphate. The water-soluble fractions (WSFs) resulting from the catalytic cellulose hydrolysis were then submitted to dark fermentation without any additional treatment. The dark fermentation step tested three different microorganisms – Enterobacter spH1, Citrobacter freundii H3 and Ruminococcus albus DMS20455 – for their ability to produce H2 from cellulose, glucose and the liquid product derived from cellulose hydrolysis. The two enteric bacteria (C. freundii H3 and Enterobacter spH1) effectively fermented the WSFs to produce H2 and other organic compounds as metabolites. For the WSFs derived from cellulose hydrolysis with ZrO2-P and ZrO2-S catalysts, the values for Enterobacter spH1 were 1.40 and 1.09 mol H2/mol hexose, respectively.

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