Stoichiometry and kinetics of poly-beta-hydroxybutyrate metabolism in aerobic, slow growing, activated sludge cultures

This paper discusses the poly-beta-hydroxybutyrate (PHB) metabolism in aero bic, slow growing, activated sludge cultures, based on experimental data an d on a metabolic model. The dynamic conditions which occur in activated slu dge processes were simulated in a 2-L sequencing batch reactor (SBR) by sub jecting a mixed microbial population to successive periods of external subs trate availability (feast period) and no external substrate availability (f amine period). Under these conditions intracellular storage and consumption of PHB was observed. It appeared that in the feast period, 66% to almost 1 00% of the substrate consumed is used for storage of PHB, the remainder is used for growth and maintenance processes. Furthermore, it appeared that at high sludge retention time (SRT) the growth rate in the feast and famine p eriods was the same. With decreasing SRT the growth rate in the feast perio d increased relative to the growth rate in the famine period. Acetate consu mption and PHB production in the feast period both proceeded with a zero-or der rate in acetate and PHB concentration respectively. PHB consumption in the famine period could best be described kinetically with a nth-order degr adation equation in PHB concentration. The obtained results are discussed i n the context of the general activated sludge models. (C) 2000 John Wiley & Sons, Inc.