Combining ABE fermentation and anaerobic digestion to treat with lipid extracted algae for enhanced bioenergy...

As a downstream process output, biobutanol can be produced via acetone, butanol, and ethanol (ABE) fermentation from lipid-extracted algae (LEA), but the leftover residue has not been treated for additional value. In current study, LEA were acid hydrolyzed to extract glucose into the hydrolysate, which was then used for ABE fermentation to produce butanol. In the meantime, anaerobic digestion was performed on the hydrolysis residue to produce methane and release nutrients for algae recultivation. To optimize butanol and methane production, several carbon or nitrogen supplements were applied. The results showed that the hydrolysate produced a high butanol concentration of 8.5 g/L with bean cake supplemented, and the residue co-digested with wastepaper had a higher methane production compared to the direct anaerobic digestion of LEA. The causes of the enhanced performances were discussed. The digestates were reused for algae recultivation and were proved to be effective for algae and oil reproduction. The combined process of ABE fermentation and anaerobic digestion was thus proved a promising technique to treat LEA for economic benefit.