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Filamentous Organisms

Long chains of bacteria. A few support floc; too many cause bulking and foam.

Filamentous organisms sketchLong filaments extending out of floc particles and bridging between them.Line sketch for orientation only. Not to scale.
Sketch: filamentous organisms as typically seen at 100x to 400x. Not to scale.

Under the microscope

Long filaments bridging between several flocs, 100x
Interfloc bridging. Filaments bridging between flocs. 100x. What this indicates: Filaments bridging floc to floc hold the flocs apart and cause bulking: high SVI and a slow settling blanket.
Dense mat of Type 021N filaments, phase contrast at 200x
Type 021N. Type 021N in large numbers. Phase contrast, 200x. What this indicates: Type 021N points to nutrient deficiency or septic, high organic acid wastes.
Parallel Sphaerotilus natans filaments with visible cells in a sheath, phase contrast at 1000x
Sphaerotilus natans. Sphaerotilus natans, cells inside a clear sheath. Phase contrast, 1000x. What this indicates: S. natans is a classic low DO filament.
Branched Gram positive nocardioform filaments, purple, at 1000x
Nocardioforms, Gram stain. Nocardioforms: Gram positive with true branching. 1000x. What this indicates: Nocardioforms go with grease, long SRT and thick brown foam on the aeration basin.
Thiothrix filaments radiating from a floc in a rosette, sulfur granules visible, phase contrast at 1000x
Thiothrix. Thiothrix filaments radiating from a floc. Phase contrast, 1000x. What this indicates: Thiothrix points to septic wastes and sulfide, or to nutrient deficiency.
Long, looping Beggiatoa filament, phase contrast at 400x
Beggiatoa. Beggiatoa, a sulfur oxidizing filament that glides. Phase contrast, 400x. What this indicates: Beggiatoa indicates septicity and sulfide in the wastewater.

Photomicrographs from Brad Musick's microscope slide collection.

See all 53 photos in the gallery

Illustrated

Capsules and sheathsLeft: rod shaped bacteria each surrounded by a clear capsule of slime. Right: a sheathed filament with cells inside a clear tube, a false branch and an empty section of sheath.How bacteria protect themselves: capsules and sheathscapsulecellempty sheathfalse branchcells inside a sheathCapsule (slime layer)Shows as a clear halo in India inkSheathA clear tube around a filament, as in S. natans
Capsules and sheaths. Bacteria with slime capsules (clear halos in India ink) and a sheathed filament with cells inside, an empty section and a false branch. What this indicates: Heavy capsule (slime) formation can cause viscous bulking, often from nutrient deficiency; a sheath and false branching help identify filaments such as S. natans. Original illustration for this site, not to scale.

See all microscopy illustrations

What you see

  • Thread like chains of cells, from short (inside floc) to very long (extending out and bridging flocs).
  • Features used for ID: length, diameter, straight or curved or coiled, branching, sheath, attached growth, cell shape, sulfur granules, Gram and Neisser stain reaction.
  • Rate abundance 0 (none) to 6 (excessive). At 4 (very common) or more, settling is usually affected.

What it may indicate

  • Low DO: S. natans, Type 1701, H. hydrossis.
  • Low F/M: M. parvicella, Types 0041, 0675, 1851, 0092.
  • Septicity and sulfide: Thiothrix, Type 021N, Beggiatoa.
  • Nutrient deficiency: Thiothrix, Type 021N.
  • Grease and long SRT: Nocardioforms, M. parvicella (often with brown foam).

What process data to check next

  • DO at 15 minute resolution, especially at peak load.
  • F/M and SRT.
  • Influent septicity: sulfide, ORP, hauled waste.
  • Nutrients: ammonia and ortho-P leaving aeration.
  • Grease loading and foam.
One slide is a snapshot. Look at trends over several days and compare with SRT, F/M, DO, SVI and effluent quality before you change anything.