SILKEBORG
The pond in Silkeborg receives runoff from a catchment with a total area of 25 ha (impermeable area of 8.8 ha). Approximately one third of the runoff water originates from a nearby housing area and the remainder from a highway. The facility is located in a park stretching into the city. The pollutant load on the catchment is considered average due to the mix of heavy traffic on the highway and low pollutant loads from the residential area. This facility shall demonstrate the efficiency of the treatment concept for averagely polluted stormwater runoff, and the capacity of the treatment units are designed for average pollutant loads.

Treatment technologies
In the pond in Silkeborg, aluminum salts are mixed flow proportionally into the incoming stormwater thereby producing insoluble aluminum hydroxide flocs with good settling properties. The aluminum hydroxide flocs have a high sorption capacity for both phosphate and heavy metals. Accordingly, these pollutants are removed by sorption and subsequent sedimentation in the pond. The principle is illustrated in the figure below.


Layout of the pond
The images below show the location (left side image) and the layout (right side image) of the pond. The inlet to the pond is located at the north-west end of the pond and the outlet is at the opposite end. Thereby the entire pond volume is utilized for settling of the aluminum flocs. A sand filter at the outlet prevents suspended particles to be discharged from the pond (Click on the images to see a larger version)



The images below show how the pond fits into the surrounding environment. It is a focal point of the TREASURE project that the treatment facilities contribute positively to an improved local environment and are that they are not percieved by the public as technical installations.





The pictures below are taken during different stages of the the construction of the pond. The first picture depicts the modeling of the pond bottom in February 2008. The second picture shows the piping and flow meters in the inflow structure.




More images from the construction phase can be seen in the file (pdf-file)