Is Your Settling Apparatus Good for Evaluating Secondary Clarifier Capacity?

State point analysis is a useful tool to evaluate the capacity of secondary clarifiers by predicting solids transport between aeration tanks and clarifiers. Using existing empirical settling models based on the functions of Sludge Volume Index (SVI) is a good starting point for designing or evaluating clarifiers. However, these models may not suit the specific situation of a particular wastewater treatment facility due to restricted data sets used for building these models. Developing the solids flux curve for the facility under evaluation is always desired. Beakers, settleometers and square beakers are good tools for qualitatively describing the settleability of biomass. They under-estimated the secondary clarifier capacity when they were used to develop the sludge settling curves. 1-L graduated cylinders with stirring and 4-L graduated cylinders without stirring generated similar limiting solids fluxes which were close to observed peak solids fluxes at the plants, while 1-L graduated cylinder tests produced a wider operating range. The settling curves based on the 4-L graduated cylinder tests fitted the field operating data better at both testing facilities. Therefore, 4-L graduated cylinders without stirring were recommended for wastewater treatment facilities to develop their own solids flux curves.Secondary clarifiers, State point analysis, Solids flux curves, and Graduated cylinders