Designing an Efficient Appurtenance for Open-Channel Flows in Combined Sewer Systems

Abstract

 An efficient sewer appurtenance for open-channel flows, applied in combined sewer systems, is presented. The facility has been successfully applied in several parts of the combined sewer system of the city of Patras (Greece) achieving combined sewage-rainwater bypass during (and soon after) storm events, where rainwater and sewage–as a mixture-flow together in a common pipe. The appurtenance ensures: a) the complete collection of the sewage flow during dry periods and its diversion to the main sewage collector pipe that concludes to the Wastewater Treatment Plant (WWTP) of the city, and b) partial drainage of the sewerage flow mixture (i.e., rainwater and sewage) to the sea (i.e., the terminal water receptor) during (and soon after) rainfall events, as a means of minimizing the excess hydraulic supply ending to the WWTP, thus maintaining its design capacity regardless the rainwater discharge conveyed by the combined sewer system. In this preliminary study, basic design characteristics of the proposed appurtenance, called diversion manhole, are given. Two different approaches to construct a diversion manhole are presented, and basic design characteristics are discussed. In the context of preliminary design hydraulic considerations, by applying basic hydraulics, it is shown that each of the proposed approaches has significant effect on the reduction of the discharge of the sewage and stormwater mixture conveyed to the WWTP during (and soon after) rainfall events.