Recent European Research into the Behavior of Sewer Sediments and Associated Pollutants and Processes

Detailed research investigating all aspects of solids in sewer systems has been underway in Europe for nearly two decades. Europe has been in the vanguard of this work, due to the historical development of sewer systems, originally as part of the industrialisation process more than 100 years ago. Continued urbanisation has caused the original sewer networks developed to serve the needs of 19th century cities to become overloaded and unable to function efficiently. Operational problems of interest include sewer blockages due to solids, loss of ability to convey (designed) flows and the construction of ‘overflows' to relieve the high flows, discharging directly into rivers and other watercourses. The recent research has characterised the nature of the solids getting into sewer systems, how they behave in terms of transport, and some of the main aspects of their effects. In a number of catchments it has been possible to demonstrate that the majority of pollutants found in suspension during storms, and likely to be discharged from overflows, originate from the predominantly organic ‘near bed solids' which accumulate in systems during dry weather. New ideas for the way in which the sediments are transported and research which has shown the importance of the transformation processes, are leading toward the development of unified and integrated understanding of the way in which sewer solids and associated processes behave. In turn this is allowing the development of more effective predictive models.