Application of CFD methods to an anaerobic digester: the case of Ontinyent WWTP, Valencia, Spain

In recent years, Computational Fluid Dynamics (CFD) methods have increasingly been used to charac-terize hydrodynamics and mass-transport in wastewater treatment units. Despite being a well-knownand widely applied treatment method to stabilize sludge before final disposal, the hydrodynamics andmass transport in the anaerobic digester have been less studied than those of other treatment units.This paper presents the preliminary results of a 3D numerical study, investigating the characteristicsof sludge flow inside the Ontinyent Wastewater Treatment Plant anaerobic digester (Valencia, Spain).An approach based upon the Reynolds Averaged Navier-Stokes (RANS) equation was applied, and clo-sure was obtained using the classical standard k– model. In this particular case, a single-phase modelwas applied considering both Newtonian and Non Newtonian behavior for the sludge simulations. Thesesingle-phase preliminary results allowed the occurrence of dead zones to be identified as well as pos-sible shortcuts inside the digester. The analysis was carried out considering the velocities and the flowpatterns inside the digester as well as the sludge volume in the digester that had lower velocities than adetermined settling velocity. The model was calibrated using available experimental pressure and tem-perature data. Finally, as well-mixed conditions are strongly desirable for effective anaerobic digestion,proposals to reduce the volume of dead zones are suggested and discussed.