Scraper Bridges

A scraper bridge is a mechanical construction forming an integral part of a waste-water treatment plant.  It is used for clearing sediment into a sludge collector pit or alternatively for depositing floating substances into a scum removal container.

There are two types available: for round basins (circular scraper bridge) and also for rectangular basins (rectangular scraper bridge).

Vandezande supplies very high-quality screw pumps and hydropower screws and offers the possibility to combine both techniques in one single screw body.  The conflicting preconditions in terms of optimum fluid levels are accommodated at the upper level by a hydraulically driven jacket valve, which also allows flow control (depending on the rotational speed) during the turbine operation, and at the lower level by means of adapted blades.

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At Vandezande, a scraper bridge consists of the following main components:

Bridge structure
The bridge consists of an aluminium box profile, a steel coated or hot-dip galvanised tube construction or a modified beam construction.  The structure spans either 1/2, 2/3 or the entire diameter of the basin. In the latter case, the two sections of the bridge are vertically hinged and connected at a distance of one metre beyond the central pivot point, so that both carriages at the end of each bridge section make maximum contact with the external perimeter wall.  This avoids any unevenness of the surface affecting the smooth distribution of the load.

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Central pivot point (circular scraper only)
The bridge is hinged at its rotation point with a grease-lubricated ball turntable.  An electric power distribution unit is integrated at the location of the central pivot point, for the supply of the power to the drive mechanism including all safety devices.

Drive unit
Circular scraper bridge
In addition to the bearing of the circular scraper bridge at its rotation point, the bridge is supported by the basin perimeter edge by means of a one or two-wheeled carriage.  The driven wheel is connected to a geared motor by means of a continuous shaft.  In the case of a two-wheeled carriage, there is an extra guide wheel in addition to the driven wheel.  The displacement speed at the external perimeter of the basin is 2.5 m/min.

Rectangular scraper bridge:
The transverse bridge is fitted with a two-wheeled carriage on both sides and with four guide wheels along the basin sides.  The driven wheels are connected to one geared motor to prevent the bridge from skewing.  The drive shaft, shell coupling and supporting bearing housings are firmly suspended on the side of the bridge.  The displacement speed at the perimeter edge is 1.8 m/min.

Furthermore, the carriage of both types of bridges is a virtually closed unit with an adjustable snow-clearing shield, an obstacle protection device and wheel slip monitoring.

Bottom scrapers
Circular scraper:
The steel bottom scrapers with a rubber sweep strip must clear the sediment from the bottom of the tank to the central sludge bag.  Two types are available: a first type where the scrapers are hinged to the bridge and are suspended and controlled using tie rods, and a second type where the scrapers are equipped with idlers running around on the bottom of the basin.

Rectangular scraper:
The bottom scrapers cover the entire width of the basin and clear the sediment to the central sludge collector pit.  The scrapers are suspended from the bridge by means of closed profiles and are kept at the correct distance from the bottom by means of wheels.  The suspension of the bottom scrapers is constructed in such a way that they can easily be inspected from the bridge after they have been raised using a (motor-driven) cable drum.

Sludge scrapers (circular scraper only)
In the central sludge collector pit, one or two sliding blades are provided and suspended from the bridge with a specially designed solid framework.  If the resistance in the sludge pit becomes too high, the blades fold up automatically.

Infeed drum (circular scraper only)
The sludge is fed into a central cylinder that flows into the top of the infeed drum.  The infeed drum forces the medium into the underlying sediment and thus preventing a short-circuit flow between the central cylinder and the overflow edge.  An additional deflection baffle can be suspended underneath the infeed drum to prevent turbulence from the sludge collector pit.  An opening has been made in the infeed cylinder to facilitate scum removal.  This opening is provided with a slide and can be operated from the bridge.

Surface scraper
Grease, oil and other floating substances are efficiently removed by a surface scraper.  In the case of a circular scraper bridge, the surface scraper is set up in such a way that all floating substances from half of the diameter of the sedimentation basin are collected and moved towards the scum removal unit.  In the case of a rectangular scraper bridge, the cleaning operation is carried out meticulously from the bulkhead at the drainage section of the basin through to the scum removal unit.


Scum removal unit
Circular scraper bridge:
The scum removal unit consists of a stainless steel collection chute, connected to a floating substance collector outside the basin by means of a gravity pipe.  A mobile scraper pushes the scum layer into the chute, after which an automatic rinsing valve flushes the installation with surface water from the sedimentation basin.

Rectangular scraper bridge:
The scum removal unit consists of a scum collector or trough, connected to a floating substance collector outside the basin by means of a gravity pipe.  The trough has enough slope in order to allow all collected floating substances to be fed into the drainage pipe.  The mobile scraper on the bridge pushes the scum layer into the collector tank.

Overflow trough cleaning
The sedimentation basin can be equipped with a trough cleaning system, which is lowered into the overflow trough during the circular movement of the bridge.  Optionally, this can be rotated by electric drive.

Vacuum cleaning unit
For both circular and rectangular scraper bridges, there is an alternative for the removal of the sludge by choosing the vacuuming option rather than scraping it to a collection point.

Environmentally conscious infrastructure

Vandezande’s activities all fit within the scope of working on an environmentally conscious infrastructure.  The construction of new locks to take transport off the road and group it in the form of shipping transport in order to further...

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