PHOSPHATE-UPTAKE KINETICS IN RELATION TO PHB UNDER AEROBIC CONDITIONS

A characteristic of the biological phosphorus removal process is the i nteraction between different intracellular components. Therefore, an u nderstanding of the effects of the intracellular components on biologi cal phosphorus removal is essential for the practical application of t he process. In this study, the stoichiometry of poly-hydroxybutyrate ( PHB) to P-uptake and the kinetics of uptake of ortho-phosphate in rela tion to PHB were investigated under aerobic and substrate limiting con ditions in batch experiments with activated sludge from a biological p hosphorus removal process. The stoichiometry of PHB to P-uptake was in vestigated by determination of the degradation rate of PHB under aerob ic conditions in the presence and absence of ortho-phosphate in the bu lk liquid. The degradation of PHB as a function of time was described by a first-order equation. The presence of ortho-phosphate increased t he rate of PHB degradation significantly, confirming that the uptake o f ortho-phosphate directly required PHB. The fraction of PHB used for uptake of ortho-phosphate from the bulk liquid was estimated to be 30% . Furthermore, batch experiments confirmed that the uptake rate of ort ho-phosphate under aerobic conditions was highly dependent on the conc entration of PHB in the biomass. The observed uptake rate of ortho-pho sphate as a function of the PHB concentration was mathematically descr ibed by a Monod equation. The maximum uptake rate of the sludge was es timated to be 14 (mg-P/g-VSS)/h. The obtained results add to the under standing of the mechanisms of the biological phosphorus removal proces s under the stress conditions with limiting substrate supplies present in the full-scale wastewater treatment process. Furthermore, the resu lts indicate that control strategies to stabilise the process should f ocus on a maintenance and optimal utilisation of PHB. (C) 1998 Elsevie r Science Ltd. All rights reserved.