Common Microorganisms

Our organism database is a guide to help wastewater operators understand what they looking at under the microscope, and the positive and/ negative impacts these microorganisms can have on wastewater plants.

This guide will cover the environmental conditions which can lead to the presence of these microorganisms, as well as the physical characteristics of most commonly occurring wastewater microorganisms. We will also cover how we use each microorganism’s environmental preferences to create an effective way to limit the growth of unwanted microorganisms while also allowing beneficial microorganisms to remain in wastewater systems.

If you are experiencing problems with any of these microorganisms, call a technical service rep at 1-888-757-9577 or visit our Lab Services page. We will work with you to resolve the conditions.


Crawling Ciliates

  • Found in healthy sludge
  • Have cilia (short hairs) that are thick and robust

Stalked Ciliates

  • Found in healthy sludge age
  • Can form large colonies with multiple heads (zooids)


  • Healthy activated sludge
  • Typically inverted bell-shaped organism

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Organism Types

Testate Ameoba

  • Have calcified protective shell called a “test”
  • Present in young sludge age

Naked Amoeba

  • Irregular-shaped mass
  • Present in young sludge age


  • Flagellates have one or more long, hair-like tail (flagellum)
  • Found in high BOD conditions and high suspended solids

Swimming Ciliates

  • Most commonly seen as ellipse-shaped with short cilia
  • Highest prevalence in slightly young sludge age



  • Have 8 legs with 4 claws on the end of each leg
  • Indicate a very old sludge age


  • Cylinder-shaped
  • Found in old sludge age


  • Have vase-shaped bodies
  • Found in moderately old sludge age


  • Have two prong adhesive tubes on their posterior
  • Can be present in any type of plant condition
Coming Soon

Filamentous Organisms




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