Stoichiometry and kinetics of poly-beta-hydroxybutyrate metabolism under denitrifying conditions in activated sludge cultures

The objective of this research was to obtain a more detailed insight in the kinetics and stoichiometry of poly-beta-hydroxybutyrate (PHB) metabolism i n activated sludge cultures. The process of storage and degradation of PHB under denitrifying conditions was studied. Dynamic conditions as occurring in activated sludge processes were simulated in a 2L sequencing batch react or (SBR) by subjecting a mixed sludge population at a sludge retention time (SRT) of about 6 days to successive periods of external substrate availabi lity (feast period) and no external substrate availability (famine period). Under these conditions intracellular storage and degradation of: PHB occur s. It was shown that the process of storage and degradation of PHB is the s ame under anoxic and aerobic conditions. About 70% of the amount of acetate consumed in the feast period is used for synthesis of PHB, and the remaind er is used for growth processes. The anoxic specific acetate uptake rate wa s 3-4 times lower than aerobically. The PHB metabolism was evaluated on the basis of a metabolic model. In a traditional macroscopic model, 10 paramet ers would be needed to describe the process. By relating these parameters t o metabolic coefficients, only 2 parameters were needed in the description. Degradation of PHB could be described by a power law equation in PHB conce ntration. The order n in these experiments equaled 0.59, close to a value p reviously reported for PHB degradation by bio-P-cultures. However, PHB degr adation by bio-P-cultures occurs at:a much higher rate. Storage of PHB in t he feast period can increase the required COD/N ratio for denitrification b y 70% compared to a situation without storage. (C) 2000 John Wiley & Sons, Inc.