Modeling reactive flows in urban water engineering

Use of reactive tracers for the calibration and validation of 2D and 3D flow models in water an wastewater treatment plants

Modeling complex systems such as highly integrated water and wastewater treatment plants requires reliable information on both transport and transformation processes.

In urban water engineering previous research has clearly focused on transformation processes, leading to ever more sophisticated models for various chemical and biological transformations. However, applying models to full-scale systems requires detailed information on actual transport processes. Even though the crucial importance of the hydraulics for plant performance is known, today's models are typically based on a much idealized representation of the flow field.

Computational fluid dynamics (CFD) has the potential to provide detailed information on transport processes and allows for additional insight in hydraulic behavior of systems that is not available today. Regarding the limitations of the current modeling approach, it gets obvious that a CFD based approach offers new perspectives. With recent advances in CFD codes and computer technology water treatment systems become amenable to this tool. From the combination of CFD with existing models for biological or chemical reactions disadvantages of today's modeling approach are overcome. Two typical representatives of complex urban water systems will be addressed, one being a disinfection reactor for drinking water treatment and the other being an aeration tank for wastewater treatment.

Focus of research

• We want to combine advanced flow modeling tools (Computational Fluid Dynamics, CFD) with sophisticated models for the transformation processes (e.g. ASM models for the activated sludge process).
• We want to develop a method for experimental validation of results from CFD models for full-scale systems which is adapted to the characteristics of urban water systems (long hydraulic residence time, slow reactions, low mixing intensity, rather large volume)
• We want to analyze dynamic interactions of loading, biological processes, aeration and flow pattern in an aeration tank of a wastewater treatment plant. We recently observed relevant aspects of such interactions and expect a significant influence on reactor performance and energy consumption of the plant.
  
  

As required performance and efficiency of urban water systems increases, the effects of non-ideal hydraulic behavior become more and more significant. Therefore, further steps to optimize these systems must pay attention to transport processes, requiring both deeper understanding of hydrodynamics and adequate modeling tools. This project contributes to that issue.