Treatment Plant Operator’s Bug of the Month is an ongoing series that spotlights the organisms present in wastewater microbiology. Each month a new organism is featured, giving readers a profile of the species and how it functions in a wastewater treatment setting. 

In this peek under the microscope, take an up-close look at testate amoebae.

Testate Amoebae and particulate BOD

Testate amoebae occur commonly in many types of wastewater treatment plants, including activated sludge, fixed film processes and lagoon systems. Testate amoebae differ from naked amoebae with the presence of a test (shell) that helps provide shelter from predators and environmental conditions. Thousands of testate amoebae species have been identified in nature and a wide range of species are observed in wastewater treatment systems. From a practical standpoint identification of individual testate amoebae species is not common. 

Testate amoebae occur under a wide range of conditions, including a wide range of sludge retention times. A general principle for growth conditions for all wastewater microbiology organisms is that they compete well when their preferred substrate is present. Low amounts of testate amoebae are typically observed, however they often proliferate when there is high amounts of particulate BOD (food) available. It is generally accepted that their test allows them to survive well in harsher conditions, including low dissolved oxygen and other stresses. It is suspected that when bacteria die and cell lysis occurs they prey well on the bug "bodies."

Getting the big picture

When testate amoebae are the predominant higher life form organism, it does not always warrant concern. However, when they proliferate higher amounts of particulate food are suspected. As a general rule, observations from microscopy require a sense of said organism abundance and comparison to the known surrounding organism types and their respective abundance forming a “big-picture” scenario. Identification and health of filamentous bacteria morphotypes and other indicator organisms helps to provide a better understanding of conditions experienced during the previous few sludge cycles, and the higher life form organisms often support these findings.

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About the author: Ryan Hennessy is the microbiology and operations specialist at Midwest Contract Operations, Inc. He was trained and mentored by Dr. Michael Richard for over 10 years in wastewater microbiology, and serves as a microbiology services consultant. Hennessy is a licensed wastewater treatment and municipal waterworks operator in the state of Wisconsin and fills in as needed for operations at several facilities. He can be reached at rhennessy@mco-us.com.