Wastewater treatment modelling combining hydrodynamics, mass transfer and kinetic
issues remains one of the major goals of chemical engineering. The reactor design is frequently
based on Activated Sludge Models (ASM) that describe the biological processes in an Activated
Sludge (AS) process. The ASM are generally implemented on ideal models of chemical reactors
that do not account for the actual hydrodynamics of the reactor. Nowadays, it is possible to obtain
hydrodynamic information of an AS tank from computational fluid dynamic (CFD) simulations
that provide information about the mass transfer in the flow field of the AS tank and enable
determining the residence time distribution (RTD). This chapter focuses on the use of CFD data
coupled to the state-of-the-art ASM1, and resumes the work developed by many researchers on
this issue. The influence of the RTD on the results of the simulations using ASM1, is analyzed
from the simulations of the ASM1 using various reactor models. A procedure is proposed for the
coupling of the CFD simulations information with the ASM1 biological model.
Keywords: Activated sludge, oxidation ditch, macromixing, residence time
distribution, activated sludge models, CFD, large eddy simulation, averaged
reynolds navier-stokes equations, turbulence models, compartmental approach.
