Raimund Bürger, Julio Careaga, Stefan Diehl, Camilo Mejías, Ingmar Nopens, Peter Vanrolleghem:
A reduced model and simulations of reactive settling of activated sludge
Denitrification during the sedimentation process in secondary settlers in wastewater treatment plants has been reported to be significant. The modelling of such a process with the conservation of mass leads to a nonliner convection-diffusion-reaction partial differential equation, which needs non-standard numerical methods to obtain reliable simulations. The purpose of this study is to present how the Burger-Diehl settler model, which models the sedimentation-consolidation process without reactions, can be extended to include biological reactions. This is done with a reduced model, having few particulate and soluble components, which can be seen as a model of the last stage of a sequencing batch reactor (SBR) process during which denitrification occurs. The main result is a numerical scheme, which has been used for simulations with different initial conditions. One outcome of the simulations is that the initial distribution of activated sludge, which in principle can be controlled by the operator of an SBR, can have a significant impact on the reduction of nitrate.