CFD modelling and optimisation of a waste water treatment plant bioreactor: A case study

This study aims to determine the optimal configuration for wall mounted mixers based on the comparison of computational fluid dynamics (CFD) modelling results to physical data collected from the treatment plant. The study was developing a CFD model of an anoxic zone-1 and simulating the fluid flow using ANSYS code ‘Fluent’. A 2D model of an activated sludge process bioreactor anoxic zone was simulated to evaluate the hydrodynamic performance and influence of the inflow through the various inlets. Furthermore, the simulation also sought to evaluate the influence on the hydrodynamic performance from structure geometry. The 2D model was able to simulate the flow pattern within the zone and results from the CFD model varied between 3% and 10% at key locations. A 3D model was also developed of the anoxic zone to further evaluate the hydrodynamic performance. The 3D model produced consistent results to the physical data collected from the plant. The hydrodynamic performance of the anoxic zone was able to be evaluated from the CFD simulations and from the physical samples collected for velocity readings and suspended solids. In the key locations, the CFD simulation showed the consistent results with the physical data. The anoxic zone was subject to velocity lower than the desired 0.3 meters per second. However suspended solid samples suggest that the zone is still within the acceptable range for specific power dissipation. Therefore, an increase in operating parameter which increases the inflow into the zone can mitigate the need for submersible mixers.