Aerated Grit Tank Improved Using CFD Modeling Techniques

Aerated grit tanks rely on air diffusers located along one wall of the tank to create a rising column of air bubbles, resulting in rotational mixing that promotes agglomeration of particles that impact the side walls and floor. Scouring velocities along the tank floor carry settled grit particles to a collection sump for removal. When retrofitting grit tanks, the tank geometry cannot be easily modified, and improvement options are limited. Computation Fluid Dynamics (CFD) modeling provides an analytical tool to mathematically model changes in mixing patterns or the addition of baffles to improve grit removal efficiency by reducing short-circuiting. Changes in the hydraulic profile caused by additional headloss in existing channels, gates, air flow, and baffling also were evaluated. This paper demonstrates how CFD modeling was used to optimize enhancements to an aerated grit removal system to handle increased flows that exceed the original basis of design.