ACOUSTIC DOPPLER CURRENT PROFILER CLARIFIER VELOCITY MEASUREMENT

Secondary clarifier performance optimization requires, in part, a complete understanding of the tank hydraulics. Clarifier depth and clarity prevent direct observation of velocity and turbulence phenomena on the spatial and temporal scale required for a complete analysis. This paper presents a technique utilizing an acoustic doppler current profiler (ADCP) to measure clarifier velocities at the temporal and spatial resolution required to understand and analyze detailed hydraulic phenomena in wastewater clarifiers.Results of ADCP measurements indicate that hydraulic flow under only the force of gravity provides significant solids transport in a sloped-floor secondary clarifiers with center-hopper sludge removal as a density-stratified flow. Implications in the design of secondary clarifier mechanisms are discussed and new insight provided into the transport of solids and purpose of the scraper mechanism in a secondary clarifier. The results suggest that the analysis of scraper mechanisms should be considered from a fluid mechanical perspective and also that a scraper-equipped, central RAS removal design creates non-ideal flow fields compared with a suction, radial removal design.The application of ADCP technology to optimization of hydraulic phenomena in secondary clarifiers and other aspects of wastewater treatment facilities promises to improve design and operation considerably. The work presented represents only an initial application of a technology with considerable potential.