A Tale of Two Methods: Comparing State Point Analysis and Computational Fluid Dynamic Modeling for Evaluating Secondary Clarifier Performance

Given the numerous tools available to evaluate secondary clarifiers, it is important to know which method provides the most reliable results. Here, a one-dimensional, graphical method (state point analysis [SPA]) is compared to a computational fluid dynamic model for secondary clarifiers (2Dc model) for evaluating secondary clarifier treatment capacity. The SPA method provides a simple approach but does not account for clarifier hydraulics or predict effluent suspended solids concentrations (ESS). The 2Dc model is more complex, but incorporates clarifier configuration and mixed liquor characteristics into dynamic analyses that predict ESS. Based on results obtained using both methods to evaluate clarifier capacity at five wastewater treatment plants, the 2Dc model was found to more accurately predict capacity than SPA when compared with field test results. This, coupled with the additional capabilities of the 2Dc model, makes it a more appropriate model to use when evaluating secondary clarifier capacities, preparing designs for new units or upgrading existing clarifiers.