Pre‐treatment and utilization of raw glycerol from sunflower oil biodiesel for growth and 1,3‐propanediol production by Clostridium butyricum

BACKGROUND: The objective of the present work is to report an efficient pre‐treatment process for sunflower oil biodiesel raw glycerol (SOB‐RG) and its fermentation to 1,3‐propanediol. RESULTS: The growth inhibition percentages of Clostridium butyricum DSM 5431 on grade A (pH 4.0) and grade B (pH 5.0) phosphoric acid‐treated SOB‐RG were similar to those of pure glycerol at 20 g glycerol L−1; i.e., 18.5 ± 0.707% to 20.5 ± 0.7% inhibition. In grade A, growth inhibition was reduced from 85.25 ± 0.35% to 32 ± 1.4% (a 53.25% reduction) at 40 g glycerol L−1 by washing grade A raw glycerol twice with n‐hexanol (grade A‐2). The kinetic parameters for product formation and substrate consumption in anaerobic batch cultures gave almost similar values at 20 g glycerol L−1, while at 50 g glycerol L−1 volumetric productivity (Qp) and specific rate of 1,3‐propanediol formation (qp) were improved from 1.13 to 1.85 g L−1 h−1 and 1.60 to 2.65 g g−1 h−1, respectively, by employing grade A‐2 raw glycerol, while the yields were similar (0.5–0.52 g g−1). CONCLUSION: The results are important as the pre‐treatment of SOB‐RG is necessary to develop bioprocess technologies for conversion of SOB‐RG to 1,3‐propanediol.