By Prof. Bob Andoh

Current estimates of the costs required to address combined sewer overflow (CSO) problems are in the $50 billion range and rising. The majority of the cost is made up of chambers and other equipment required to separate solids and disinfect the much higher volume of stormwater-sewage mix that is generated during heavy rains. These estimated costs are based on the use of conventional technology, which requires relatively large sedimentation and contact tanks in order to achieve the level of solids separation or disinfection needed to meet applicable environmental regulations.

Hydrodynamic vortex separators (HDVSs) have been identified as a possible means of reducing the capital expenditures required to address CSOs. A key advantage is that a single HDVS is capable of both solids separation and disinfection, providing a significant reduction in the capital expenditures required to handle CSOs. Another advantage is that the flow properties of a single HDVS can be optimized to greatly improve the efficiency of both solids separation and contact disinfection compared to conventional technology. This means that HDVSs can handle the same CSO volume as conventional contact tanks that are 5 times larger. The resulting reduction in tank size and construction costs typically reduces overall project costs by about 50%.