Not only preventing backflows: Flap gates for the estimation of separate sewer overflow volumes
2015 (English)Conference paper, Presentation (Refereed)
In practice discharges of untreated wastewater occur from many wastewater sewer systems, often via Sanitary Sewer Overflows (SSO). The untreated wastewater from SSO can be transferred through the overflow systems into receiving waters, reducing their quality and bringing risks to human health and aquatic organisms. Increased awareness of the negative effects of SSOs has led to the development of various control measures as part of watershed protection programs around the world. However, the information the number of SSO events is often unknown due to poor or limited monitoring. A further problem is that backflows can occur through an overflow system, with receiving waters entering the wastewater network due to elevated levels of the receiving waters. This additional relatively clean water often increases the volumes of water that need to be transported to the treatment facility and dilutes wastewater pollutants, resulting in lower treatment efficiency and higher costs for chemicals, increasing electricity consumption for any intermediate booster pumps and within the treatment plant. This paper illustrates how the flap gates, commonly used for preventing these backflows, also can be used for the estimation of SSO discharge volumes. An experimental full-scale setup was designed where sewage flowed through a flap gate between two chambers with a constant flow rate. The stabilised water heads in the two chambers and the flow rate were measured. Experiments were performed for both dry and submerged flap gate conditions (the latter is relevant for the SSO event occurring during high water level in the receiving waters). In total, five flap gates with opening dimensions of 200, 300, 400, 500 and 600 mm were tested and flow rating curves were established with high precision (R2>0.99). Results of the opening pressure tests showed some deviations between the values specified by the manufacturer of the flap gates and the experimentally obtained opening pressure values. An approach to generalising the flow rating curves for other than tested diameters of the flap gates is suggested. The usage of flow rating curves for estimation of the volume is discussed. This study showed that the water head measurements before and after the flap gate can provide a reliable and inexpensive method for quantification of the SSO discharge volumes.
Place, publisher, year, edition, pages
Research subject Urban Water Engineering
IdentifiersURN: urn:nbn:se:ltu:diva-32825Local ID: 76f0664b-7cd9-4808-8233-f7c35c3f81b8OAI: oai:DiVA.org:ltu-32825DiVA: diva2:1006059
NORDIWA 2015 : Nordic Wastewater Conference 04/11/2015 - 06/11/2015
Godkänd; 2015; 20160126 (olepan)2016-09-302016-09-30Bibliographically approved