A Guide to Identifying and Treating Wastewater Microorganisms

Our wastewater microorganisms database is a guide to identify what operators are looking at under the microscope, what is causing it, and provide a course of treatment when needed. We will dive into the biological process and identify the positive and negative impacts these organisms can have on wastewater plants by providing in-depth knowledge of the wastewater treatment process.

This guide will cover the environmental conditions which can lead to the presence of numerous lifeforms including bacteria, filamentous organisms, protozoa, metazoa, plants, algae, and a number of other microorganisms. It will also cover the physical characteristics of the most commonly occurring organisms, and how we use their environmental preferences to create an effective way to limit the growth of unwanted organisms while also allowing beneficial organisms to remain in wastewater systems.

If you are experiencing problems with any of these wastewater 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.

Filamentous Organisms


  • Moves in slow, gliding motion 
  • Found in low D.O. conditions


  • Moves in a flexing motion
  • Present in low D.O. conditions

Haliscomenobacter hydrossis

  • Rigid toothpick-like appearance
  • Found in low D.O. conditions

Nostocoida limicola

  • Has tangled structures
  • Found in plants with nutrient deficiencies

Type 0092

  • Typically appears straight or slightly bent
  • Found in plants with high levels of incoming fats, oils, and greases (FOG)

Type 1851

  • Has rectangular-shaped cells
  • Found in plants with low F:M conditions

Sphaerotilus natans/Type 1701

  • Can have attached growths and false branching
  • Found in plants with low D.O. in system


  • Has rectangular-shaped cells
  • Found in plants with low D.O. conditions

Type 021N

  • Has disk-shaped cells
  • Found in plants with nitrogen deficiency

Microthrix parvicella

  • Has tangled spaghetti-like appearance
  • Found in plants with high incoming fats, oils, and greases (FOG)

Type 0041 / Type 0675

  • Has square-shaped cells with occasional irregularity
  • Found in plants with low F:M conditions

Nocardia-like Organisms

  • Has true branching
  • Found in plants with old sludge age


Testate Amoeba

  • 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

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



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


  • Cylinder-shaped
  • Found in old sludge age

Bristle Worms

  • Segmented bodies
  • Have bristles along their body



  • Long and thin 
  • Found in low D.O. conditions


  • Diameter measures between 30-60µm
  • Present in low pH conditions


  • Four-cell cluster
  • Found in nitrogen deficient conditions


  • Growths are amorphous or finger-shaped
  • Found in high levels of soluble BOD


  • Pear-shaped
  • Found in clean water


  • Flea-shaped
  • Found in low available BOD conditions

Plants & Algae


  • Round to elongated cells
  • Appears red when exposed to too much sunlight


  • Green in color
  • Lemon-shaped cells


  • Green in color
  • Contains branched filaments

Green Flagellate Algae

  • Green in color, but can appear red
  • Have a red eyespot


  • Small oval or spherical-shaped floating plant
  • Green in color


  • Small light green, floating plant
  • Can occasionally have visible roots


  • Contain a single row of cells
  • Cells’ shape ranges from long cylinders to short rectangles


  • Have spherical-shaped cells
  • Single cells that form gelatinous colonies


  • Spherical cells connected by thin strands
  • Green in color


  • Size and shape widely vary
  • Can be free floating or attached to other algae/plants


  • Usually seen as four-celled colonies
  • Spines attached to the outside cells


  • Green in color
  • Cells are longer than they are wide


  • Single-celled
  • Spherical

Dolichospermum (Anabaena)

  • Green colored coiled filaments
  • CBead or barrel-shaped cells


  • Coiled filamentous cyanobacteria that can be loose or tight
  • Found in clusters


  • Green in color
  • Short and branched filamentous alga


  • Has thick filaments with no sheath
  • Discoid cells that are blue green in color with fine granulation