Abstract Summary (Max 250 words)
Mixing systems in wastewater treatment plants consume a major share of overall energy, creating a persistent trade-off between process reliability, sufficient mixing performance, and energy efficiency. To address this challenge, a comprehensive methodological framework for the comparative evaluation of different propeller geometries was developed as part of a government funded project called RIOWAR (funding code 03EN2092C). Computational Fluid Dynamics (CFD) and electrical resistance tomography (ERT) were applied under well-defined and reproducible boundary conditions to systematically assess mixing efficiency. A process-tomography test rig incorporating ERT was used to assess mixing time. Mixing time was quantified at a target homogeneity of 90%, using methods well-documented in the literature. Scaling laws based on the similarity theory were applied to ensure dynamically similar flow conditions across the laboratory model and the full-scale propeller. CFD models were validated through flow measured by time-resolved Particle Image Velocimetry (PIV). The study followed an iterative design–simulate–evaluate workflow in which simulation outcomes directly informed the development of improved propeller geometries, trageting an enhanced or similar mixing performance at reduced energy input. While comparing different propeller laboratory models, it was found, that at higher rotation rates the optimized geometries reduced the mixing time by 10 to 20 % compared to the established geometry. In future research the application of the optimized propeller geometry shall be investigated in real-scale environments.
