Identification:  Amoebae are single celled microorganisms. Amoebae are motile by pseudopodia, also known as "false feet". Amoebae are divided into two different types, testate and naked. Testate amoebae are those that have shells (or tests) and naked amoeba do not have shells. The shells can be proteinaceous or siliceous shells. A naked amoeba might make you think of the movie "The Blob" as they can slowly spread out their protoplasm in any direction. They eat by engulfing their food. They ingest their prey by phagocytosis.  They range in size from 10-200 µm. Amoebae typically grow and divide; this pattern of vegetative growth may or may not include encysted states, flagellated forms, or a transition from a sexual to an asexual phase of growth.

Additional Information: Amebas belong to the Phylum Protozoa. Some  types amoeba are found in the class Sarcodina and the order Rhizopoda. Heliozoa is another group of amoebae, although they are less common in activated sludge and found more in lagoon type systems.  Some types (genera) of amoebae commonly found in wastewater are Arcella, Euglypha, and Centopyxis.

If the biomass is really old and rotifers and nematodes are usually present, and all of a sudden large numbers of amoebae show up, check to see if a sudden spike of BOD has occurred.  Adjustments to RAS and wasting may need to be made in order to handle the sudden increase in BOD. Addition of biological products can also help overcome sudden spikes in BOD to help recover quicker and reduce changes or BOD or TSS permit violations.

How to Find Them: Microscopic examination of a wet mount. Some of the larger amoebae can be seen at 40-100s and 200x. Sometimes there may be tons of really small naked amoeba that require the use of 400x or even 1000x in order to clearly see them. This usually happens when a sudden spike of BOD has happened.