8 Chain and Flights Scrapers for the WWTP Sensetal – Laupen, Switzerland


In May 2017 and following to an open tender ARA Sensetal and Tschuda concluded the contract for the renewal of the chain and flights scrapers in the 4 final sedimentation tanks of the WWTP in Laupen.

ARA Sensetal is operating one of the biggest sewage treatment plants in the Swiss canton of Berne and is cleaning the waste water of 27 municipalities.

Due to the existing design Tschuda has installed 2 units KKR Plastic Chain Scraper in each of the 4 final sedimentation tanks having a length of approx. 79m and a width of 7,5m. Both chain scraper systems move the bottom sludge to the return sludge hoppers located close to the middle of the tank. Therefore the two units within the same tank also have to move in opposite direction.


The return guide rails for the scraper flights are located lower at the 4 chain scraper units located closer to the inlet of tanks. The scraper flights of these systems have to move below the water surface back to the inlet of the tank. The scum at the water surface is only removed by the second scraper system starting close to the middle of the tank and moving the scum to the removal units located at the end of the tanks.

Scraper flights with brushes for cleaning the clear water effluent pipes

All 4 final sedimentation tanks have submerged clear water effluent pipes with openings on the top of the tubes.

To prevent any blocking of these openings by algae growing in the basins, each of the tanks is equipped with 14 special scraper flights. These scraper flights are installed at the KKR Plastic Chain Scraper working at the effluent side of the tanks and each of the special flights is carrying a brush with a length of approx. 1m.

Due to the design with roller guides the scraper flights move in exact upright position on the return guide rails and the chain scraper systems therefore can brush off any sludge and algae from the top of the submerged effluent pipes at least twice at each turn around.


The take over of all 8 new chain and flights scraper systems was done in September 2017.

Finally we would like to thank the operator, ARA Sensetal, and also the consulting engineer, Hunziker Betatech AG, for the good cooperation:
Due to the perfect preparation works done by the operator, Tschuda could install the equipment for each final sedimentation tank, so 2 pcs. KKR Plastic Chain Scraper, within just one week and of course already inlcuding a complete test run in dry conditions.