Anaerobic digestibility of algal bioethanol residue

The aim of this work was to investigate anaerobic digestibility of algal bioethanol residue from saccharification and fermentation processes. A series of batch anaerobic digestion tests using saccharification and fermentation residue showed that the maximum methane yields of saccharification residue and fermentation residue were 239 L/kg VS (Volatile Solids) and 283 L/kg VS (Volatile Solids), respectively. Energy recovered by anaerobic digestion of the residue was 2.24 times higher than that from the ethanol produced in the main process. 5-HMF (5-hydroxymethylfurfural), a saccharification byproduct, could retard methanogenesis at over 3 g/L however, the inhibition was prevented by increasing cell biomass concentration. Anaerobic digestion of residue has the potential to enhance bioenergy recovery and environmental sustainability of algal bioethanol production.

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► Algal ethanol production generates residue retaining >70% of biomass as energy basis.
► Anaerobic digestion of residue recovered energy 2.24 times higher than ethanol.
► Maximum CH4 yields of algal ethanol residue ranged 239–283 L/kg VS.
► Inhibition of a saccharification by product can be prevented by increasing cell biomass..