Protozoans are single-celled organisms. They can serve as indicator organisms to identify the health of a wastewater system. They can also help identify toxic events and recovery from upsets.


Amoeba amoeba2

Amoebas are often found in young sludge in a “start-up” plant, after a toxic event or after a wash-out. They can appear in naked and testate forms. When an amoeba is in testate form, they are in a protective shell from their outside environment, indicating a potentially threatening situation or a recent upset.


flagellate FlagellateFlagellates move using their single “tailed” flagella. They feed on free bacteria in the system and need a high level of BOD in the system to maintain their energy for motility and feeding. They are a step up on the evolutionary scale from the amoeba and are found in slightly older sludge.

Free-Swimming Ciliate

Free Swimming Ciliate flagellate2Free-swimming ciliates move using small “hairs” called cilia. These are present in a maturing sludge system and indicate an overall healthy environment for your sludge.

Crawling Ciliate

crawling_ciliate crawling_ciliate2 crawling_ciliateCrawling ciliates have specialized cilia called cirri that allow them to crawl over and around the floc in a wastewater system. These are often found in well-stabilized systems.

Carnivorous Ciliate

Carnivorous CiliateCarnivorous ciliates are free-swimming ciliates that feed on flagellates and other smaller ciliates. They are often found in healthy wastewater systems.

Stalk Ciliate

Stalk Ciliate stalk_ciliate2Stalk ciliates can be seen in both colonial and single forms. The stalk length indicates their age, with older organisms having longer stalks. During an upset, the ciliate heads can break off from their stalks to find a more compatible living environment. They have cilia on the ends of their heads that allow them to move food into their “mouths.”


Suctorian suctorian2Suctorians have the ability to produce a toxic substance on their microtubules to capture their prey. They can be found with stalks or free of stalks. They are commonly found in nitirifying plants and in a stable biomass environment.