2-42: Mechanistic investigations of ultrasound mediated bioconversion of glycerol to bioalcohols by immobilized Clostridium pasteurianum

Glycerol, the principal byproduct of biodiesel production, can be a valuable carbon source for bioconversion into diverse class of compounds including alcoholic biofuels . This work attempts to investigate the mechanistic aspects of ultrasound mediated bioconversion of glycerol to mixed bio-alcohols by immobilized Clostridium pasteurianum cells on silica support. Our approach is of coupling experimental results with simulations of cavitation bubble dynamics and enzyme kinetics. In addition, the statistical analysis, analysis of variance of experimental results was also done. The glycerol uptake by cells was not affected by either immobilization or with ultrasonication. Nonetheless, both immobilization and ultrasonication were found to enhance glycerol consumption. The enhancement effect of ultrasound on glycerol consumption was most marked (175%) at the highest glycerol concentration of 25 g/L (271.7 mM). The highest glycerol consumption (32.4 mM) was seen for 10 g/L (108.7 mM) initial glycerol concentration. The immobilization of cells shifted the metabolic pathway almost completely towards 1,3-Propanediol (PDO). No formation of ethanol and butanol were seen with mechanical shaking, while traces of ethanol were detected with ultrasonication. On the basis of analysis of enzyme kinetics parameters we attribute these results to increased substrate-enzyme affinity and decreased substrate inhibition for 1,3-PDO dehydrogenase in presence of ultrasound that resulted in preferential conversion of glycerol into 1,3-PDO.