Sludge handling with many process benefits and low life-cycle costs

Lackeby Peripheral driven scraper is a peripheral driven sludge scraper designed for installation in large circular tanks and designed with a rotating scraper bridge. Lackeby Peripheral driven scraper is manufactured in different versions but especially in the following two types;

– the excess sludge is sucked up into several tubes and transferred to the middle of the tank by hydrostatic pressure – a so-called suction sludge scraper.

– the sludge is transferred to the basin centre, where it is pumped away for further treatment. Normally the floating sludge is removed at the peripheric wall close to the outlet flume.


  • Low investment costs
  • Many references in excellent operation
  • Reliable
  • Low maintenance- and operating costs
  • Can be installed in pools up to 65 meters in diameter
  • Optimum bridge design
  • Advantageous sludge removal system


Equipment for collection of biological sludge are based on a scraper arrangement which takes care of both sedimented bottom sludge and floating sludge. The Sludge scraper is designed with a peripherally driven rotating bridge with a scraper system which is mounted to the bridge. Lackeby Peripheral driven scraper is equipped with a rotating bridge, a centre layer and a solid rubber coated wheel which runs on the wall at the tank periphery. There are different types of scraping systems with several kinds of scraper blades and so-called logarithmic designed scrapers, in both cases, sludge is removed at the centre of the tank, but also there are various types of suction sludge scrapers.


Technical features
  • New screenings washing system
  • New press pipe cleaning system
  • New through design
  • New spiral design
  • New press system – Higher dry solids
  • Secure operation
  • Robust design
  • Simple inspection via a hatch in the press unit

Tank design

The tank centre is designed as inlet and support of the scraper.
Basins for mud scrapers are normally designed with the basin floor sloping towards the centre to facilitate sludge scraping. For biological sludge a relatively large sludge pit is made in the centre of the basin or as a circular sludge pit around the centre pillar.

Basins with suction sludge scrapers are normally designed with horizontal tank bottom as the absorption of sludge is evenly distributed along the tank radius.
The tank’s outlet system is depending on the sludge which is to be separated. It is important that the outlet channel, etc. is designed so that the rotating bridge can be fitted with a suitable cleaning system in order to minimize the manual work as much as possible.

The basin wall is serving as a support for the drive wheel and deviations in height of the wall must be avoided in order to achieve a long life of the driving wheel.

Drive units are available in various sizes and are as standard fitted with overload protection and control systems.

The drive units are available with a ball-bearing of suitable quality and size. The wheels are generally made of cast iron furnished with rubber or polyurethane, all to achieve maximum grip and as long life as possible. The drive is performed with a gear motor that provides an appropriate peripheral speed for the application. The gearbox is by default connected via an electronic rotary guard that stops the motor at overloads. The unit is located in the control cabinet.

The sludge removal system is chosen depending on the type of sludge that must be removed. As mentioned above, the sludge settles to the bottom of the tank and is scraped against the centre of the tank of canted or logarithmically shaped bottom scrapers where it is carried forward for treatment. Greater sedimentation tanks which separate biologic return sludge can be equipped with a suction sludge system which has the advantage of creating a low sludge retention time which may be necessary for the operation of such facilities.

Electrical power is transferred from the outer edge of the basin under the floor up through the centre pillar and pulled by a moulded, waterproof pipe by polyethylene tubing or alike. The power cables are connected at the top of the centre pillar to a slippering ring via an electrical box. The slippering ring contains the appropriate number of connection devices and can be fitted with gold or silver rings for better transfer of signal data.
Cabling between the slip ring unit, control cabinet and various motors and switches are placed in special cable trays or tubes.


  • Cleaning Brushes, fixed or rotating, are available in various designs and also a container for de-icing fluid can be used to improve the operation during the winter season.
  • A flocculation chamber can be installed in the middle part of the basin and is hung in the rotating bridge. 2 or 4 pieces flocculation mixers may in these cases be installed on the bridge.
  •  Floating sludge removal is made by a scraper blade which is attached to the rotating bridge. It is designed so the float sludge is forced from the centre to the periphery where it is automatically removed from a fixed surface sludge box. The sludge box is available with a flushing system to minimize manual service.
  • Control system and electrical cabinet can upon request be delivered to be located on the bridge. The cabinet contains motor groups, relays, controls for rotation guards, lights, emergency stops, main switch, etc., all for the safe operation of the facility. The control system for the scraper is designed for fully automatic operation, 24 hours a day. If the scraper is furnished with a hydrostatic pressure sludge removal system the removal is controlled either automatically or manually, depending on installation requirements. The floating sludge removal system is normally semi-automatic, but is also available for automatic operation; in any case if pumps are installed they are level-controlled. When flocculation mixers are used they run 24 hours a day and start and stop manually. The Control cabinet’s enclosures are available in different design and in many cases made of stainless steel.

Principal for suction sludge scraper

The suction sludge scraper is used when large amounts of bulky sludge shall be removed. The design is used mostly in larger basins in order to achieve a lower retention time of the sludge which would have been the case if a conventional scraper had been chosen. In Figure 1.1 below is design (1) inlet, (2) outlet and (3) is the rotating bridge which is operated by a geared motor which is located on the first of the drive carrier’s wheels.

Lackebys solution has a number of V-shaped scraper blades (4) and suction sludge pipes (5), for a satisfying removal of sludge from the bottom of the tank. The hydrostatic pressure forces the sludge through the suction sludge pipes which are designed so that they always remove sludge effectively and thereby avoid clogging the system. The suction sludge pipes are fixed with steel bars that are connected to the bridge and the upper part of the tubes are connected to a horizontal and opened sludge flume (7) which has separate flow switches (6) for each sludge pipe.

The sludge channel collects the sludge from the suction sludge pipes and transports it to the outlet (9), in the centre of the tank through a siphon pipe, (8).
The start-up of the siphon system is made with a hand pump or a motor driven ejector pump (12).
The sludge is transported to the pump pit (11), through a sludge pipe (10) under the bottom of the tank. The outlet is equipped with a regulating device for control of the sludge and the system is designed to keep the hydraulic losses at a minimal level.

Principal for sludge removal at the centre

The sludge scraper is designed to remove excess sludge from the bottom and at the same time scrape surface sludge to a surface sludge removal box.

The scraper system is hung in the bridge and equipped with scraper blades that are designed logarithmically, which means that the sludge is forced to the tank centre.

The floating sludge scraper is also mounted under the bridge. The floating sludge scraper is designed to move the floating sludge to the tank periphery and into a fixed sludge box.