Usage Functions

The peripheral traction crane is a machine used to remove biological sludge and supernatant from circular sedimentation tanks in the primary and secondary sedimentation section of civil and industrial wastewater treatment plants.

Profile Thomson


Structural features

The peripheral traction scraper crane is usually installed in reinforced concrete sedimentation or decanters. The machine consists of a mobile beam resting, at the center, on a rotating support and, at the periphery, on a traction carriage. The operation is managed by a combined reducer motor located in the peripheral area of the walkway.

Wastewater enters the concrete tank through a central cylinder that distributes the liquid inside the tank itself. Thanks to the slow rotation of the equipment, and thanks to the difference in specific weight, the sludge settles to the bottom of the tank, while the supernatant and foam float to the surface. The supernatant is conveyed to the foam collection trough via the surface scrapers.

Finally, the clarified water overflows through a system of Thompson profile weirs located in the peripheral part of the tank and is introduced into the appropriate perimeter channel to be removed from the plant. The presence of an adequate central recirculation zone and the flocculation compartment allows for the adequate coagulation and flocculation of the water, which completes its clarification in the outermost zone. The sludge scraper blades made of 304 stainless steel remove the sludge precipitated on the sloping bottom of the tank and collect it in a central sump. This machine is available for tanks of different diameters according to the customer’s needs.


  • Quick installation
  • High capacity for the removal of biological sludge and supernatant.
  • Easy application even on existing tanks
  • Possibility of supervising and/or replacing the bottom scrapers from above without the need to empty the tank
  • Reduced maintenance costs


  • Peripheral traction crane with double walkway and double bottom scraper
  • Materials: stainless steel AISI 304 L / 316 L / painting: Immersed parts in AISI 304 – Emerged parts in Hot-dip galvanized carbon steel


  • Scum box foamer blade
  • Thomson profile
  • Scumbox foam collection trough
  • Scum baffle
  • Bottom scraper blade
  • Central deflector
  • Mobile beam with walkway function
  • Lateral traction carriage
  • Central pin
  • Walkway with useful width, complete with Keller grating, handrail, parapets and toe kick in compliance with current safety regulations

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