Enhanced acetone-butanol-ethanol production by clostridium beijerinckii using biochar

Acetone-butanol-ethanol (ABE) fermentation medium contains expensive buffer and mineral stock solutions, which account for approximately 84% of the total medium cost. Biochar has the potential to serve as an inexpensive pH buffer and source of mineral and trace metal nutrients in ABE fermentation. In this study, biochars from four different sources (switchgrass, SGBC; forage sorghum, FSBC; redcedar, RCBC; and poultry litter, PLBC) were used to replace 4-morpholineethanesulfonic acid (MES) buffer and mineral stock solutions in the fermentation medium. Biochar-free media with (Ctrl A) and without (Ctrl B) MES buffer and minerals were used as controls. Fermentations using C. beijerinckii were performed at 35 °C in 250 mL bottles with 50 mL working volume for 72 h. During fermentation, the pH in the treatments without MES buffer was adjusted to above 5.0 to avoid acid crash. Liquid samples were withdrawn at 12 h interval for organic acid and ABE analysis. Additional samples were withdrawn at 0 h and 72 h for elemental analysis using inductive-coupled plasma (ICP) spectrometry. With careful pH adjustment, ABE production in treatments with SGBC (17.3 g/L), FSBC (17.0 g/L), RCBC (18.2 g/L) reached to similar level as Ctrl A (17.5 g/L). However, Ctrl B without MES buffer showed a sluggish ABE production (4.3 g/L). Elements released from biochar during fermentation provided nutrients and pH buffer that enhanced ABE production. This study demonstrates that biochar can serve as cost-effective substitute for mineral and buffer solutions in ABE fermentation.