Sludge Treatment & Dewatering: Tanks For Wastewater Treatmetnt

Sludge Treatment & Dewatering – sludge is generally a thick, soft, wet mud or a similar viscous mixture of liquid and solid components which is a product produced during the refining process of wastewater treatment.

Being such a simple word suggests the way it looks and covers a multitude of materials, many very different from each other with the common denominator, despite appearances, is that they generally have very high water content. With ever-increasing costs involved in its disposal, sludge treatment is becoming one of the greatest costs in running an effective wastewater treatment plant.

The sludge treatment is necessary to reduce and ameliorate the sludges, which are produced within the biological wastewater treatment.  When looking at a sludge from a treatment process there could be fewer solids in it than there is. A typical DAF plant sludge will be approximately 5% solid or 95% water equating to 19 tonnes of water and 1 tonne of solids from a 20-tonne load of sludge.  There are a lot of costs saving opportunities hereby increasing the solids content to reduce total material removed from a site by tanker and put more of the water down the drain.

Process of Sludge Treatment

This process comes in two stages:

1) Making a good liquid-solid separation of the sludge so that the water is ready to separate effectively from the solids by means of Biological or chemical treatment.

2) Make a physical separation of the liquid and the solids so through means of equipment such as filter press’s so as much water can be “squeezed” out of the sludge and disposed of to drain.

Sludge from biological wastewater treatment products various types of sludge.

  • Raw sludge, which is sludge in its untreated non-stabilized state, can be taken from wastewater treatment plants. It tends to acidify digestion and produces odour.
  • Primary sludge is produced through the mechanical wastewater treatment process. It consists of wastewater contaminations and is generally the sludge amassing at the bottom of the primary sedimentation basin/tank. This sludge tends to consist of a high portion of organic matters, faeces, textiles, paper etc. The consistency is a thick fluid with a water percentage between 93 % and 95 %.
  • Activated Sludge is the removal of dissolved organic matter and nutrients from the wastewater that take place in the biological treatment step. It is done by the interaction of different types of bacteria and microorganisms, which require oxygen to live, grow and multiply in order to consume the organic matter. The resulting sludge from this process is called activated sludge. The activated sludge exists normally in the form of flakes, which besides living and dead biomass contain adsorbed, stored, as well as organic and mineral parts.
    Return activated sludge flows from the biological aeration basin into the final clarifier. The activated sludge flakes settle down to the bottom and can be separated from the cleaned wastewater. The main part of the separated sludge, which is transported back to the aeration basin, is called return activated sludge.
  • Tertiary sludge is produced through further wastewater treatment steps e.g. by adding a flocculation agent.

Sludge Thickening

A volume reduction of approximately 30 – 80 % can be reached with sludge thickening before further treatment. This is where wastewater treatment plants drive the sludge off regularly and usually takes place directly in the sludge storage tank.


Further reduction of the sludge amount is mostly necessary after the thickening as the liquid still must be dewatered to a dry and porous form. Dewatering is generally by machine processes by means of a filter press and centrifuge.  Enduramaxx works with several industrial wastewater treatment companies who offer advice on wastewater and sludge treatment covering coagulation, chemical treatment flocculation, biological treatment, pH control and dewatering. Enduramaxx can offer a range of bulk chemical tanks, dosing tanks, polymer mixers, coagulation and flocculation equipment – for more details please get in touch.

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