Polyhydroxyalkanoates (PHAs) have been recognized as good substitutes for the non-biodegradable petrochemically produced polymers. However, their high (real or estimated) current production cost limits their industrial applications. This work exploits two strategies to enhance PHAs substitution potential: the increase in PHA volumetric productivity in high density cultures and the use of waste glycerol (GRP), a by-product from the biodiesel industry, as primary carbon source for cell growth and polymer synthesis. Cupriavidus necator DSM 545 was used to accumulate poly(3-hydrozybutyrate) (P(3HB)) from GRP and from commercial glycerol (PG) as control substrate. On PG, productivities between 0.6 g(PHB) L(1) h(-1) and 1.5 g(PHB) L(1) h(1) were attained. The maximum cell DW was 82.5 g(DW) L(1), the P(3HB) content being 62%. When GRP was used, 68.8 g(DW) L(-1) with a P(3HB) accumulation of 38% resulting in a final productivity of 0.84 g(PHB) L(1) h(-1) was obtained. By decreasing the biomass concentration at which accumulation was triggered, a productivity of 1.1 g(PHB) L(1) h(1) (50% P(3HB), w/w) was attained using GRP. P(3HB) molecular weights (M(w)) ranged from 7.9 x 10(5) to 9.6 x 10(5) Da. (C) 2009 Elsevier Ltd. All rights reserved.