17 May 2019

How is sludge treated in a wastewater treatment plant?

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 Sewage sludge is produced in the wastewater treatment process and is composed of organic and inorganic materials.

Disposing of this matter can be expensive and harmful to the environment, so it is important for companies to minimize the production of sludge. 


There are three different types of sludge produced in wastewater handling, that need to be minimized to save disposal costs:

  • Primary sludge - this is produced by settleable solids that are removed from raw wastewater.
  • Secondary sludge - a product of biological processes, such as biofilm accumulation. This sludge contains microorganisms that have grown on the biodegradable matter, that were not removed in primary settling.
  • Chemical sludge - this variant is produced when chemicals are introduced to wastewater with the aim of changing unwanted dissolved materials into a solid state, for easy removal.

Sludge is treated using the following steps:

  1. Thickening - this stage reduces its overall volume and enables easy handling.
  2. Digestion - organic solids then decompose, further reducing the total mass.
  3. Dewatering - the remaining sludge contains high water levels, it is important to remove this before disposal by drying the sludge.
  4. Disposal - at this point, dried sludge can be reused as fertilizers or incinerated if it is deemed too toxic for the receiving environment.


Due to the rising costs of disposal, it is important to seek new ways to minimize the production of sludge during the wastewater treatment process. By reducing the volume of wet sludge, it reduces the dry mass and leads to less end product to dispose of. An effective way to reduce the volume of wet matter would be to reduce the primary level of organic material.

NCH facilities’ are experts in wastewater treatment solutions such as their BioAmp delivery system with FreeFlow™ bacteria. This program will digest organic waste that leads to sludge build ups. It is effective in drain lines, septic tanks, and sewage treatment systems. 

Read this case study on how NCH helped a company in Singapore with a BioAmp treatment solution.


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