Biological butanol production from microalgae-based biodiesel residues by Clostridium acetobutylicum

•Butanol production from microalgae biodiesel residues via ABE fermentation.•More than twofold of butanol yield increase with additional butyrate of 18–20g/L.•The highest butanol production of 3.86g/L was achieved with residues of 300g/L.•The highest butanol yield of 0.13g/g-carbohydrate was with residues of 100g/L.•One third of carbohydrate from residues cannot be utilized by C. acetobutylicum. This study conducted batch experiments to evaluate the potential of butanol production from microalgae biodiesel residues by Clostridium acetobutylicum. The results indicated that with 90g/L of glucose as the sole substrate the highest butanol yield of 0.2g/g-glucose was found, but the addition of butyrate significantly enhanced the butanol yield. The highest butanol yield of 0.4g/g-glucose was found with 60g/L of glucose and 18g/L of butyrate. Using microalgae biodiesel residues as substrate, C. acetobutylicum produced 3.86g/L of butanol and achieved butanol yield of 0.13g/g-carbohydrate via ABE fermentation, but the results indicated that approximately one third of carbohydrate was not utilized by C. acetobutylicum. Biological butanol production from microalgae biodiesel residues can be possible, but further research on fermentation strategies are required to improve production yield.