Author(s)

B. De Clercq, D.J. Kinnear & P.A. Vanrolleghem

Abstract

Optimization of the solids removal performance of a clarifier requires, in part, a complete understanding of the tank hydraulics. This paper presents velocity measurements obtained by utilizing an acoustic doppler current profiler (ADCP). The latter provides the necessary temporal and spatial scale to understand and analyze in a detailed way density-driven flows m wastewater clarifiers. Velocity profiles and Reynolds shear stresses of a full-scale installation were investigated. Two different clarifiers were investigated that differ in floor slopes and solids removal mechanisms. The ADCP revealed that sloped clarifiers provide significant solids transport towards the central removal sump. Implications in the design of clarifiers are discussed and new insight is provided into the transport of solids and purpose of the solids removal system. The velocity measurements suggest that the analysis of the removal mechanism should be considered from a fluid mechanical perspective. It was also seen that a scraper-equipped, central solids removal design creates non-ideal flow fields compared with a suction, radial removal design. Shear stress corresponded well with simulation results from literature. The paper has to be seen as a first attempt to apply this proven measurement technology in wastewater treatment.

Keywords