This case study explores the findings from a detailed flow analysis conducted on three different wastewater treatment reactors. In these reactors, component ‘A’ is intended to be removed from the wastewater stream by converting it into component ‘B’. However, the original reactor design exhibited a significant parasitic reaction, where ‘A’ was also converted into an unwanted byproduct, component ‘C’.
The hypothesis posited that the parasitic reaction was attributable to high concentrations of ‘A’. The Dynaflow Research Group (DRG) was commissioned to investigate the differences in flow patterns among three reactor configurations: the original design and two modified layouts. Each reactor features air injection at the bottom, wastewater introduction at a higher point, and effluent removal at an elevated location. The aim of the new layouts was to enhance water circulation within the reactor by optimizing the positions of the air and wastewater inlets.
Analysis
DRG utilized Computational Fluid Dynamics (CFD) to simulate the detailed flow patterns within the reactors. Given that buoyant forces, resulting from air bubbles in the water, drive the main reactor dynamics, a two-phase Euler-Euler approach was employed to model both the liquid and gaseous phases.
To quantify the concentration of component ‘A’ throughout the reactor, it was modeled as a passive scalar, transported by convection and diffusion. A high concentration pulse of component ‘A’ was introduced through the water inlet at a specific time. The duration required for the reactor to achieve a homogeneous concentration of ‘A’ served as an indicator of the reactor’s mixing efficiency.
Results
The analysis revealed that achieving proper mixing in the original reactor took approximately 2.5 times longer than in the two modified reactors. The original design’s homogeneous air inlet did not establish a distinct flow direction, resulting in suboptimal mixing. In contrast, the new reactor configurations demonstrated clear upward and downward flow regions, leading to enhanced flow velocities and improved circulation. Consequently, the mixing performance of the reactors was significantly improved.
Conclusion
The study underscores the importance of optimizing flow patterns in wastewater treatment reactors to mitigate the impact of parasitic chemical reactions. By implementing distinct flow directions through strategic placement of air and wastewater inlets, the efficiency of mixing within the reactors was markedly improved.
