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The Effect of Shear Stress on Sewer Deposits with Respect to TSS, Vss and COD Release

Author(s): R. Veldkamp; A. Schellart; S. Tait; R. Ashley

Linked Author(s): Simon Tait

Keywords: Sewer deposits; Erosion; Shear stress; Total suspended solids; Volatile suspended solids; COD; Turbidity

Abstract: This paper provides an overview and some results of a collaborative study by the Pennine Water Group and the Delft University of Technology. It describes erosion tests in an annular flume at WL|Delft Hydraulics in which real in-sewer sediment deposits were formed under carefully controlled environmental conditions and then subjected to a series of increasing shear stresses. The sewer sediments were collected in the UK (Dundee) and in the Netherlands (Loenen). During the erosion tests total and volatile suspended solids concentration and COD concentrations were determined from discrete samples. DO levels were recorded continuously. During one test, with Loenen sediments the turbidity of the sewage in the flume was monitored continuously with the same type of turbidity sensor as was used for field measurment in the Loenen sewer system. Direct observations show how the occurrence of bed forms causes a step-change in mean shear stress. Biological activity in sewer sediment beds appears to reduce the resistance to erosion within short timescales.


Year: 2003

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