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Dewatering equipment are used to perform dewatering on construction sites, which is defined as the process of separating water from another material like saturated soil or sludge. The separation of water is performed by using a force generated by vacuum or centrifugal motion.

Dewatering equipment saves money by reducing solids handling and disposal expenses. It is an alternative and economical option compared with heat drying systems for water removal.

The selection of dewatering equipment depends on the corrosion potential of the material removed and the contaminants present in the liquid. As the reactivity of the liquid increases, the equipment is constructed with more durable materials.

This article describes the different types of dewatering equipment used in construction sites and the factors affecting their selection.

Types of Dewatering Equipment

The common types of dewatering equipment are:

  1. Centrifuges
  2. Drying beds
  3. Vacuum filters
  4. Filter presses
  5. Sludge lagoons
  6. Gravity and low-pressure devices

1. Centrifuges

Centrifuges remove solids from liquids through the process of sedimentation and centrifugal force. As shown in Figure-1, the solids or sludge are fed through the stationary feed tube. The sludge moves with an acceleration through the ports in the conveyor shaft, which is then distributed to the periphery of the bowl.

Diagram of a typical dewatering centrifuge
Figure-1: Diagram of a typical dewatering centrifuge
Image Courtesy: Global Environment Centre

The bow spins at high speed which simultaneously separates water from the solids. The separated solids are compacted against the bowl wall, as shown in the figure. The solids are then conveyed to the centrifuges drying stage and the liquid separated is discharged continuously over the weir arrangements around the sides of the bowl.

2. Vacuum Filters

A vacuum filter is an equipment that creates a vacuum to draw water from the solids. As shown in Figure-2, the filter consists of a drum submerged on a cake or sludge. A filtering medium is placed over the drum. The whole arrangement of valves and pipes is such that the vacuum is applied to the inner side of the filter medium when the drum rotates. The rotation of the drum draws water from the sludge. When the drum carries the sludge to the atmosphere, the cake layer formed is chipped by a knife blade as shown in the figure.

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Diagram depicting rotary drum vacuum filter operation and process flow
Figure-2: Diagram depicting rotary drum vacuum filter operation and process flow
Image Courtesy: Komline-Sanderson

The use of vacuum filters avoids the need for heat treatment or digestion before disposal or incineration process.

3. Filter Presses

This equipment uses a filter medium to separate solids from the liquids. A filter press captures the solids in the pores between two or more porous plates.

Diagram depicting the layout of a filter press, including sludge flow and components
Figure-3: Diagram depicting the layout of a filter press, including sludge flow and components
Image Courtesy: Lenntech BV

The solids captured are then pushed into the cavities by forcing water over them either through plate pressure or by build-up solid pressure.

4. Drying Beds

The arrangement of drying beds is shown in Figure-4 . It consists of a perforated or open joint drainage pipe placed within a layer of gravel base, which is again covered with a layer of sand.

Diagram depicting operation of a drying bed
Figure-4: Diagram depicting operation of a drying bed
Image Courtesy: VCCS.edu

The sludge collected is placed over this sand layer and allowed to dry. The water from the sludge is removed by evaporation and by gravity movement to the underlying gravel base. This water is taken out through the drainage pipe placed in the gravel base.

With time, the sludge dries, and cracks develop on the surface. These cracks allow the evaporation of lower layers of the sludge.

The design parameters of a drying bed includes:

  1. Depth of sludge
  2. Moisture content of sludge
  3. Availability of sand bed area

5. Sludge Lagoons

Sludge lagoons are excavated areas that are used to deposit and dry the sludge for several months to years. The depth of a sludge lagoon can vary from 2-6 feet.

Diagram depicting the operation of a lagoon
Figure-5: Diagram depicting operation of a lagoon
Image Courtesy: VCCS.edu

6. Gravity and Low-Pressure Devices

These devices make use of a set of drying beds and low pressure pressing devices. The low-pressure belt presses and the gravity bed allows increased solid-water separation.

Photo of a gravity belt thickener
Figure-6. Photo of a gravity belt thickener Image Courtesy: Siemens, Scheel & Company, Inc.

The equipment offers simplicity, low cost, less noise, low energy, and maintenance costs. This is a good choice for smaller treatment and operation plants.

Dewatering Equipment Selection Considerations

The selection of the most effective dewatering equipment for construction activities is dependent on:

  1. Drying requirements
  2. Cost
  3. Sludge characteristics
  4. Available area

The drying requirements and cost constraints are the primary factors governing the selection of the dewatering equipment.

An engineer or industrial buyer must be aware of the sludge characteristics or corrosion potential of the water to be dewatered. The solids separated may possess hazardous contaminants or undesirable composition that may affect the performance of the equipment. For highly reactive sludge, the dewatering equipment like filter presses or gravity/low-pressure devices demand chemical conditioning prior to dewatering.

FAQs

What are dewatering equipment in construction?

Dewatering equipment are used to perform dewatering, which is defined as the process of separating water from another material like saturated soil or sludge. The separation of water is performed by using a force generated by vacuum or centrifugal motion.

What are the common dewatering equipment used in construction?

The common types of dewatering equipment are:
1. Centrifuges
2. Drying beds
3. Vacuum filters
4. Filter presses
5. Sludge lagoons
6. Gravity and low-pressure devices

What are sludge lagoons?

Sludge lagoons are excavated areas that are used to deposit and dry the sludge for several months to years. The depth of a sludge lagoon can vary from two to six feet.

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