Holistic Evaluation and Optimization of Primary Clarifier Performance: Using Advanced Modeling to Address Flow Split and Performance Imbalances in Primary Clarifiers

摘要

The Philadelphia Water District (PWD) owns and operates the Southwest Water Pollution Control Plant (SWWPCP), which receives combined sewage from its collection system. As a part of the utility's CSO management plan, PWD and Hazen undertook an extensive study of the available SWWPCP peak flow treatment capacity using several sets of calibrated models. The primary sedimentation tanks (PSTs) at the site were modeled with calibrated fluid dynamics (CFD) models to evaluate current performance, assess available capacity, and identify performance limitations. In addition, calibrated hydraulic modeling was used to assess flow splits, and any potential flow imbalances, between individual PSTs and calibrated process modeling was used to assess the impact of PST performance on the aeration process mixed liquor concentrations (MLSS) and resulting secondary clarifier performance. This combined modeling approach was used to confirm that the SWWPCP's PSTs could adequately protect secondary treatment performance at flows beyond the current rated peak flow capacity and to identify thresholds at which additional PST construction would be required. The combined modeling work provided a holistic evaluation of the performance of the PSTs and its impacts on treatment plant performance.