CFD simulation of a novel anaerobic-anoxic reactor for biological nutrient removal: Model construction, validation and hydrodynamic analysis based on OpenFOAM®

•A CFD model is developed and validated by means of experimental tracer tests.•Different modelling approaches are successfully applied for reactor elements.•Dead volumes and channelling are located and quantified through model simulations.•Mixing quality is confirmed by means of uniformity index analysis.•A deflector is essential for maintaining the anaerobic-anoxic multi-environment.