Production of polyhydroxyalkanoates from agricultural waste and surplus materials

To be competitive with common plastics, the production costs of polyhydroxyalkanoates (PHAs) have to be minimized. Biotechnological polymer production occurs in aerobic processes; therefore, only about 50% of the main carbon sources and even a lower percentage of the precursors used for production of co-polyesters end up in the products wanted. A second cost factor in normally phosphate-limited production processes for PHAs is the costs for complex nitrogen sources. Both cheap carbon sources and cheap nitrogen sources are available from agricultural waste and surplus materials and make a substantial contribution for minimizing PHA production costs. In this study, fermentations for PHA production were carried out in laboratory-scale bioreactors on hydrolyzed whey permeate and glycerol liquid phase from the biodiesel production using a highly osmophilic organism. Without any precursor, the organism produced a poly [3(hydroxybutyrate-co-hydroxyvalerate)] copolyester on both carbon sources. During the accumulation phases, a constant 3-hydroxyvalerate content of 8 - 10% was obtained at a total PHA concentration of 5.5 g/L (on hydrolyzed whey permeate) and 16.2 g/L (glycerol liquid phase). In an additional fermentation, an expensive nitrogen source was substituted by meat and bone meal beside the glycerol liquid phase as a carbon source, resulting in a final PHA concentration of 5.9 g/L.