Authors

R.Y.G. Andoh, H. Carter, C. Osterrieder, N. Raymond & M.A. Stein

Abstract

Faced with the challenge of addressing Combined Sewer Overflow (CSO) issues, the City of Saco, Maine, adopted an approach which involved improving the transport and management of excess wet-weather flows by implementing a scheme that applied advanced vortex technologies for both flow control and water quality improvement. The application of vortex technology at Saco utilizes vortex flow regulators in the upstream diversion chambers to regulate maximum flows to the existing wastewater treatment plant in order to avoid hydraulic overloading and the diversion of excess combined sewer flows to the new CSO treatment facility. The new facility utilizes an advanced hydrodynamic vortex separator (HDVS) that incorporates a novel non-powered, self-activating and self-cleansing CSO floatables control screening system and accomplishes primary treatment equivalency, disinfection, floatables capture and grit removal all in one vessel. The underflow from the CSO facility comprising sewer debris and solids including grit, sediments, settleable organic solids and floatables, is returned to the headworks at the treatment plant and the clarified, screened and disinfected overflow is discharged to the receiving environment (Saco River) after de-chlorination. The ability to perform several essential unit processes (i.e. Sedimentation, Screening, Disinfection and Grit Removal) all in one vessel resulted in significant savings in the overall project scheme costs on account of the more compact design of the advanced HDVS system coupled with the elimination of additional tanks and vessels that would have been required with the conventional approach. Analytical results from post-construction compliance monitoring have confirmed the efficacy of the system.