Alcoholic Biofuels Production from Biodiesel Derived Glycerol by Clostridium pasteurianum Whole Cells Immobilized on Silica

Abstract

Clostridium pasteurianum cells immobilized on silica were used as biocatalysts for bioconversion of both pure and biodiesel-derived crude glycerol to butanol, 1,3-propanediol (PDO) and ethanol. Among five concentrations (1, 2, 3, 5, 10 % w/v) of cell immobilized support studied, 3 % w/v cell immobilized support performed the best and was chosen for further studies. The cross-linked cells produced higher amount of solvents than non-cross linked cells. The flow cytometric results revealed that presence of pure as well as crude glycerol had no adverse effect on cellular morphology of C. pasteurianum. The maximum yields of butanol, ethanol and 1,3-PDO obtained with immobilized cells were 0.36 (25 g/L pure glycerol), 0.11 (10 g/L pure glycerol) and 0.54 g/g (10 g/L pure glycerol), respectively. Among the three crude glycerol concentrations studied, 25 g/L crude glycerol gave maximum yield of n-butanol (0.23 g/g), and 5 g/L crude glycerol formed maximum 1,3-PDO (0.61 g/g). Only traces of ethanol were detected at all concentrations of crude glycerol studied. A comparison of free and immobilized cells revealed that immobilized cells performed better than free cells for mixed alcohols production at higher concentrations of both pure and crude glycerol. Thus, the use of immobilized cells is a viable option for converting high concentrations of biodiesel derived crude glycerol into alternate energy sources.