Combination of Field Testing and CFD Modeling for Optimum Clarifier Design


  • Irene Chu, Alonso Griborio, Paul Pitt - Hazen and Sawyer
  • Meei-Lih Ahmad, Guoji Chiu, Jignesh Desai - San Francisco Public Utilities Commission – Wastewater Enterprise
  • Eugene Ling - San Francisco Department of Public Works

CFD Model of Existing Clarifier at SOR 1060 gpd/sf .

Like many utilities, the San Francisco Public Utility Commission (SFPUC) Southeast Wastewater Treatment Plant (SEP) is facing critical upgrades of its aging secondary clarifiers. The SFPUC SEP is a high purity oxygen activated sludge plant that treats an average dry weather flow of 58 mgd. SEP was designed to treat a dry weather flow of 85 mgd and wet weather flows of up to 250 mgd of which 150 mgd receives secondary treatment. SEP has sixteen 120-ft diameter circular secondary clarifiers each with a side water depth (SWD) of 15-ft. The clarifiers are divided into two parallel sets, the north and south, each with 8 clarifiers, a mixed liquor (ML) distribution channel and return activated sludge (RAS) wet well and pumping station.

The SFPUC is currently planning to upgrade the existing 30 year old clarifiers. Computational Fluid Dynamic Modeling was used to evaluate potential changes to the clarifiers including enlarged center wells, internal baffling and energy dissipating inlets. The goal of this effort was to replace the aging internal mechanisms and structures with modern clarifier components that can improve clarifier performance rather than replace in kind.

As SEP and other utilities plan to upgrade their secondary clarifiers, many are considering modern features rather than replacement in kind. This paper details the development and utilization of CFD modeling to evaluate potential clarifier upgrades for the SFPUC SEP.

For more information, please contact the author at

Hear about new publications with our email newsletter

We will never share your details with anyone else.


Newsletter Newsletter

Horizons Fall 2017 (pdf)

Horizons showcases significant water, wastewater, reuse, and stormwater projects and innovations that help our clients to achieve their goals, and can help you achieve yours. Articles are written by top engineers and process group leaders, demonstrating and explaining the beneficial application of a variety of technologies and tools.

View previous issues »