Hydraulic optimization of a combined sewer overflow (CSO) storage facility using numerical and physical modeling

A commercially available 3-D computational fluid dynamics (CFD) model (STAR-CD) was used to investigate capacity upgrading options for a combined sewer overflow (CSO) facility of inadequate capacity. The numerical model was verified against the data collected in two physical models. The need for verifying the CFD model was given by the complexity of the CSO facility, which comprises several interconnected tanks. The verified numerical model was then applied to analyze hydraulic conditions in the whole facility for major structural modifications with the aim of reducing or eliminating untreated overflows from the facility. Many scenarios were proposed and tested in the study and the two most promising structural modifications, scenarios 1 and 2, are presented in the paper. Both appeared to meet the design condition of increasing the facility capacity to 60  m³/s, but better performing scenario 1 would be significantly more costly to implement than scenario 2. Even though the study focused on a particular CSO facility, hydraulic conditions in the studied facility represent general flow conditions in typical CSO or stormwater settling facilities and, therefore, the numerical modeling methods used are applicable to solving a wide range of hydraulic problems encountered at similar facilities.