High storage of PHB by mixed microbial cultures under aerobic dynamic feeding conditions

Activated sludge submitted to aerobic dynamic feeding conditions showed a high and stable capacity to store polyhydroxybutyrate (PHB). The influence of carbon and nitrogen concentrations on the PHB accumulation yield was studied in a range of 30 Cmmol/l to 180 Cmmol/l for acetate and between 0 Nmmol/l and 2.8 Nmmol/l for ammonia. Low ammonia concentrations favored PHB accumulation. The maximum PHB content, 67.5%, was obtained for 180 Cmmol/l of acetate supplied in one pulse but with a slower PHB storage rate. In order to avoid substrate inhibition, 180 Cmmol/l of acetate were supplied in two different ways: continuously fed and in three pulses of 60 Cmmol/l each. In both cases the specific PHB storage rate increased and the PHB content obtained were, 56.2% and 78.5%,respectively. Addition of acetate by pulses controlled by the oxygen concentration was kept for 16 days. The PHB content was always above 70% of cell dry weight.