A two-stage bioprocess for hydrogen and methane production from rice straw bioethanol residues

This study evaluates a two-stage bioprocess for recovering hydrogen and methane while treating organic residues of fermentative bioethanol from rice straw. The obtained results indicate that controlling a proper volumetric loading rate, substrate-to-biomass ratio, or F/M ratio is important to maximizing biohydrogen production from rice straw bioethanol residues. Clostridium tyrobutyricum, the identified major hydrogen-producing bacteria enriched in the hydrogen bioreactor, is likely utilizing lactate and acetate for biohydrogen production. The occurrence of acetogenesis during biohydrogen fermentation may reduce the B/A ratio and lead to a lower hydrogen production. Organic residues remained in the effluent of hydrogen bioreactor can be effectively converted to methane with a rate of 2.8 mmol CH4/gVSS/h at VLR of 4.6 kg COD/m3/d. Finally, approximately 75% of COD in rice straw bioethanol residues can be removed and among that 1.3% and 66.1% of COD can be recovered in the forms of hydrogen and methane, respectively.

► A two-stage bioprocess recovers H2 (1.3%) and CH4 (66.1%) from rice straw bioethanol residues. ► Acetogenesis may potentially reduce the B/A ratio and lead to a lower hydrogen production as well. ► Clostridium tyrobutyricum was the major H2 producer in the H2 bioreactor.