Development and validation of a flux-based stoichiometric model for enhanced biological phosphorus removal metabolism

Enhanced biological phosphorus removal (EBPR) is a wastewater treatment pro cess involving metabolic cycling through several biopolymers (polyphosphate , polyhydroxyalkanoates. and glycogen). This metabolic cycling is induced i n microorganisms by treatment systems that alternate between initial carbon -rich, anaerobic environments followed by carbon-poor, aerobic environments . While the appearance and disappearance of these biopolymers has been docu mented, the intracellular pressures that lead to their synthesis and degrad ation are not well understood. To understand how carbon, energy, and redox potential are channeled through the metabolic pathways in each treatment pr ocess stage, a metabolic flux model that contained a complete set of the pa thways involved in biomass synthesis and energy production in bacteria was developed. The model accounts for the energy requirements of macromolecule synthesis and of metabolite transport across the cell membrane, The equatio ns for the 163 reversible and 166 irreversible reactions were solved using linear optimization. Data from a laboratory scale sequencing batch reactor performing EBPR were used as model inputs. Given polyhydroxyalkanoate synth esis and glycogen degradation rates in the anaerobic phase, the model predi cted reasonable anaerobic acetate uptake and polyphosphate consumption rate s. In the aerobic phase, the polyphosphate and glycogen synthesis rates wer e used to predict the polyhydroxyalkanoate consumption rate. In addition, t he model predicted the ratio of acetate uptake to phosphate release observe d experimentally, as well as an inverse relationship between polyhydroxyalk anoate and polyphosphate consumption. The model provides information on the pathways by which the energy-rich molecules ATP, NADH, and NADPH are produ ced and consumed during the EBPR processes. In doing so, it supports the hy pothesis that biopolymer metabolism provides a means for organisms to balan ce intracellular energy supplies. Moreover. the model suggests pathways at which metabolic regulation should occur and provides a comprehensive accoun t of EBPR metabolism. (C) 1998 Elsevier Science Ltd. All rights reserved.