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Free-Swimming Ciliates

Ciliates that swim between flocs eating dispersed bacteria. Paramecium, Litonotus, Aspidisca (crawler).

Free-swimming ciliates sketchOval cells covered in short cilia swimming in the liquid between flocs.Line sketch for orientation only. Not to scale.
Sketch: free-swimming ciliates as typically seen at 100x to 400x. Not to scale.

Under the microscope

Slipper shaped free-swimming ciliate with two dark round bodies inside, next to a floc, phase contrast
Free-swimming ciliate. Slipper shaped free-swimming ciliate beside a floc. Phase contrast. What this indicates: Free swimmers feed on dispersed bacteria. Many of them often means a younger sludge or a cloudy background.
Oval crawling ciliate with its cirri (tufts of fused cilia, labeled cilia), phase contrast at 400x
Crawling ciliate. Crawling ciliate with its cirri (fused cilia) visible. Phase contrast, 400x. What this indicates: Crawlers grazing on floc, together with stalked ciliates, suggest a stable, well flocculated sludge.

Photomicrographs from Brad Musick's microscope slide collection.

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Illustrated

Protozoa groupsSix panels: an amoeba with pseudopods, small flagellates with whip like flagella, an oval free-swimming ciliate covered in cilia, a crawling ciliate walking on floc, two bell shaped stalked ciliates on a floc, and a suctorian with knobbed tentacles on a stalk.The six protozoa groups operators trackAmoebaeFlowing pseudopods, slowYoung sludge, startupFlagellates5 to 20 microns, whip like tailYoung sludge, high soluble BODFree-swimming ciliatesCovered in cilia, fastYounger sludge, dispersed bacteriaCrawling ciliatesWalk on floc with cirriStable, well flocculated sludgeStalked ciliatesBells on stalks, ring of ciliaMature, stable sludgeSuctoriansTentacles catch other protozoaMature, older sludgeGreen text: what a large number of each group usually suggests. Line drawings, not to scale.
The six protozoa groups. Original line drawings of amoebae, flagellates, free-swimming, crawling and stalked ciliates and suctorians. What this indicates: Which group you see most of hints at sludge age: amoebae and flagellates for young sludge, crawling and stalked ciliates and suctorians for mature sludge. Original illustration for this site, not to scale.

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What you see

  • Oval or elongated cells covered with cilia, moving quickly between flocs. Typically 50 to 300 microns.
  • Common examples: Paramecium (slipper shaped), Litonotus (long neck), Colpidium.
  • Crawling ciliates such as Aspidisca and Euplotes walk on floc surfaces using fused cilia (cirri); note them separately.

What it may indicate

  • Free swimmers feed on dispersed bacteria, so many free swimmers often means plenty of dispersed cells.
  • Common in moderately young sludge, during recovery, or with a higher F/M.
  • Crawling ciliates (Aspidisca, Euplotes) with stalked ciliates suggest a stable, well flocculated sludge.
  • Free swimmers dominating with a cloudy background: dispersed growth, possible short SRT or overloading.

What process data to check next

  • SRT and F/M.
  • Effluent turbidity and settleometer supernatant clarity.
  • Recent wasting changes or load increases.
  • DO in the first zone.
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.