Production of PHB from crude glycerol

Crude glycerol-a by-product of the large scale production of diesel oil from rape-is examined for its possible use as a cheap feedstock for the biotechnological synthesis of poly(3-hydroxybutyrate) (PHB). The glycerol samples of various manufacturers differ in their contamination with salts (NaCl or K2SO4), methanol or fatty acids. At high cell density fermentation these pollutants could possibly accumulate to inhibiting concentrations. The bacteria used were Paracoccus denitrificans and Cupriavidus necator JMP 134, which accumulate PHB from pure glycerol to a content of 70% of cell dry mass. When using crude glycerol containing 5.5% NaCl, a reduced PHB content of 48% was observed at a bacterial dry mass of 50 g/L. Furthermore the PHB yield coefficient was reduced, obviously due to osmoregulation. The effect of glycerol contaminated with K2SO4 was less pronounced. The molecular weight of PHB produced with R denitrificans or C. necator from crude glycerol varies between 620000 and 750000 g/mol which allows the processing by common techniques of the polymer industry.