The inhomogeneity of sewer sediment bed material in terms of physical and pollution characteristics is known. To quantify the variations over time and depth of bed deposits an extensive study investigating the properties of bed deposits in a combined interceptor sewer in the city of Hildesheim was carried out. High temporal variations as well as vertical gradients of bed characteristics were found especially for pollution characteristics (chemical and biochemical oxygen demand) and volatile solids content; physical parameters (bulk density, total solids content) appeared to vary less. The fluctuations were related to degradation processes in the sediment bed and exchange processes between bed deposits and sewage.

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