The effects of formic acid, acetic acid and levulinic acid on acetone-butanol-ethanol (ABE) fermentation under different pH adjustment conditions were investigated using Clostridium acetobutylicum as the fermentation strain. CaCO3 supplementation can alleviate the inhibitory effect of formic acid on ABE production. The ABE titers from the medium containing 0.5 g L-1 formic acid with pH adjusted by CaCO3 and KOH were 11.08 g L-1 and 1.04 g L-1, which reached 64.8% and 6.3% of the control group, respectively. Compared with CaCO3 pH adjustment, fermentation results with higher ABE titers and yields were obtained from the medium containing acetic acid or levulinic acid, when the pH was adjusted by KOH. When formic acid, acetic acid, and levulinic acid co-existed in the medium, better fermentation result was achieved by adjusting the pH by CaCO3. Moreover, 12.50 g L-1 ABE was obtained from the medium containing 2.0 g L-1 acetic acid, 0.4 g L-1 formic acid, and 1.0 g L-1 levulinic acid as compared to 3.98 g L-1 ABE obtained from the same medium when the pH was adjusted by KOH. CaCO3 supplementation is a more favorable pH adjustment method for ABE medium preparation from lignocellulosic hydrolysate.
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