Exploring temporal variations of oxygen saturation constants of nitrifying bacteria

Activated sludge models (ASM) are generally accepted as state-of-the-art in modeling wastewater treatment plants. In this paper, we assess the temporal variability of an ASM parameter - the oxygen half-saturation constant of autotrophic bacteria (KO,AUT). A series of respirometric experiments is performed for conventional activated sludge and sludge from a membrane bioreactor. K-O values are estimated for both ammonium-oxidizing and nitrite-oxidizing bacteria. For parameter estimation, the Monod kinetic model structure is extended by a sensor model. Still remaining systematic deviations between data and model are considered by a thorough residual analysis: (1) uncertainty estimates of K-O are corrected to reflect model structure deficiencies and (2) the inter-experimental cross-correlation of residuals is taken into account to assess temporal changes. We conclude that K-O,K-AUT is a time variable parameter and should be considered accordingly. (C) 2006 Elsevier Ltd. All rights reserved.