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 https://www.w3.org/1998/Math/MathML" display="inline"> 30 C m m o l / 1 to https://www.w3.org/1998/Math/MathML" display="inline"> 180 C m m o l / 1 for acetate and between https://www.w3.org/1998/Math/MathML" display="inline"> 0 N m m o l / 1 and https://www.w3.org/1998/Math/MathML" display="inline"> 2.8 N m m o l / 1 for ammonia. Low ammonia concentrations favored PHB accumulation. The maximum PHB content, https://www.w3.org/1998/Math/MathML" display="inline"> 67.5 % , was obtained for https://www.w3.org/1998/Math/MathML" display="inline"> 180 C m m o l / l of acetate supplied in one pulse but with a slower PHB storage rate. In order to avoid substrate inhibition, https://www.w3.org/1998/Math/MathML" display="inline"> 180 C m m o l / 1 of acetate were supplied in two different ways: continuously fed and in three pulses of https://www.w3.org/1998/Math/MathML" display="inline"> 60 C m m o l / l each. In both cases the specific PHB storage rate increased and the PHB content obtained were, https://www.w3.org/1998/Math/MathML" display="inline"> 56.2 % and https://www.w3.org/1998/Math/MathML" display="inline"> 78.5 % , respectively. Addition of acetate by pulses controlled by the oxygen concentration was kept for 16 days. The PHB content was always above https://www.w3.org/1998/Math/MathML" display="inline"> 70 % of cell dry weight.