Booming ski tourism at Mount Trysil, Norway's largest alpine ski sports resort a few hours drive from Oslo, has exhausted existing wastewater treatment facilities. A new, nature-based facility has been put into service, which functions virtually like a closed circuit, discharging nothing other than clean water back to the land.
Odourless basin
"The proviso was for a so-called nature-based treatment plant, used only for freestanding homes or small clusters of houses to date. The new plant had to service 3,500 people, and it is working fine," says project manager Tore Østeraas from COWI in Norway.
In 2008, another 2,000 people will be hooked up to what was built originally built as a trial plant.
The plant features an open basin yet is still completely odourless, a result achieved by the simple use of small pellets of burned clay.
Clay pellets in two places
Wastewater is ducted into a sealed chamber, where liquids are separated from solids in a rotary filter before continuing out into the open basin. This is where the clay pellets – also known as light weight aggregates – enter the picture. They create a thick, insulating layer on the basin's surface, preventing the contents from freezing, despite temperatures of –30 degrees Celsius, at the same time checking all smells.
The fine slurry sinks to the bottom of the basin, and the sewage water is pumped out to be cleansed of phosphorus. This takes place in a special filter, equipped with another layer of small clay pellets. The purified water is finally discharged into a stream. The remaining solid sewage is transformed into odour-free compost by adding heat and bacteria in just days.
Efficient purification
Tore Østeraas sees several benefits to the plant: "We achieve efficient purification using simple methods, as well as the plant being cheap to run. What's more, we don't add any chemicals. I think this sort of treatment works will be the thing of the future in many areas where sewerage is not feasible." By Eva Isager, jaje@cowi.com Published: 26.04.2007