Sludge dewatering

What is Sludge Dewatering? – Overview of Sludge Thickening & Dewatering

Sludge watering refers to the process of reducing waste volume in preparation for its efficient disposal. The wastewater is treated before it can be released into the environment. Sludge forms during this process. Sludge, which is a by-product of wastewater treatment in industrial and municipal settings, has been a problem for water treatment companies for a long time. The sludge can be dewatered with a filter press to reduce its weight and volume before it is disposed.

What is “Sludge”?

Simply put, “sludge” can be described as a semi-solid slurry produced by a variety industrial and municipal processes.

Sludge dewatering serves the purpose of efficiently and reliably concentrating wastes into high-solids filter cakes that can be disposed of easily and economically. There are strict regulations regarding the disposal of sludge. Many companies, municipalities, or institutions have sustainability goals that comply with regulations and meet their organizational and environmental requirements.

What is the Purpose of Sludge Dewatering?

Sludge dewatering is a process that separates sludge from liquids and solids in order to minimize waste. There are many options for dewatering sludge, including geomembranes, plate and frame filter presses, belt filter presses and screw pressing. There are many other options.

Important to remember that dewatering does not treat the liquid or sludge. It only separates the liquid and solid components to make it easier and cheaper to dispose of the individual phases. After the sludge is dewatered, the liquid and solid components might contain contaminants that need to be removed.

What is the Dewatering Process?

Thickening or Dewatering both produce a concentrated, consolidated product. This retains most of the solids in the original sludge and a diluted stream that is predominantly water. Both of these processes send the dilute stream back to the wastewater treatment plant.

The thinning processes concentrate the sludge by removing a portion of the -free water. The finished product retains the liquid-free-flowing characteristics and can be transported by pumping. Normally, the dry solids content is increased by thickening to around 4-6%.

The sludge water content is removed significantly during dewatering to create a concentrated sludge product, with a DS concentration typically between 15 and 45%.

This product is known as a cake. It forms lumps that can only be transported using a conveyor belt, machine earth-moving equipment or spade.

To remove more water than that which is possible with thickening, dewatering processes use a substantial mechanical force. These processes work by:

  • To force the water (or filtrate), through the sludge, press the filter (belt filter press, screw pressing or filterpress).
  • To force the denser solids and water to adhere to the vessel’s internal walls, rapidly rotate the sludge inside a cylindrical vessel. The water will form the diluted centrate stream ( centrifugation).
  • Passing the sludge along a narrow flow channel with porous walls, through which the filtrate flows ( Rotary press).
  • Allowing the liquid to evaporate in ambient conditions (sludge drying lagoons), or both evaporate and drain under gravity using a permeable medium (sludge dry bed).

Benefits of Sludge Dewatering

Waste Volume Reduction

Sludge dewatering is a weight- and volume-reduction method that minimizes waste disposal costs. As the name suggests, water removal is the main means to reduce the volume of sludge before it can be economically disposed off.

Lower Transportation Costs

Management of sludge is a difficult business. Dry, high solids cakes mean lower costs. The use of dewatering equipment can be an effective tool to manage sludge accumulation and reduce storage costs.

Consistent dryness with lower risk of leaching

Consistent cake dryness is achieved by sludge-dewatering filter presses. Dry, high solids cakes are less expensive to transport and have a lower chance of leaking onto roads. This is especially important when trucks are passing through residential areas.

Wastewater Recycling

Recycling wastewater is another advantage of sludge-dewatering. Industries and communities can reclaim the water after it has been treated with sludge. The water is not potable but it can still be used for many purposes. Reclaimed water can be used to benefit a community or company by steam powered plants.

Equipment can be easily automated

Many people think that filter presses are labor-intensive equipment. But, in fact, sludge dewatering presses can come with automatic cloth washers, mechanically-assisted cake release, and sophisticated control systems, allowing communication to the main plant control system, all making sludge dewatering much easier.


Sludge dewatering can be environmentally friendly because it reduces the volume of waste and makes it easier to dispose. The dry cakes can be disposed off, but the reuse of the filtrate could reduce the need for water for treatment in municipal or industrial wastewater plants and reduce overall water consumption.

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