Indicator protozoa are easily observed under low magnification (100x) under a light microscope. These wastewater protozoa are actually single celled, eukaryotic organisms that "feed" on bacteria cells in the water. As they are larger and more complex organisms than their prey (bacteria), protozoa are often used to judge the "health" of your bacteria (bugs).
Under times of high loadings, low dissolved oxygen, and general stress; we tend to see more primitive protozoa (flagellates). As the amount of soluble BOD/COD decreases and dissolved oxygen becomes more available the protozoa population becomes more complex with free-swiming ciliates, crawling ciliates, and stalk ciliates becoming increasingly common.
I have included a picture from a refinery activated sludge plant with a stalk ciliate attacted to the bacterial floc. When you see stalked ciliates in a wastewater system you generally have good floc formation, sufficient dissolved oxygen (DO), and efficient BOD/COD removal.
Erik Rumbaugh has been involved in biological waste treatment for over 20 years. He has worked with industrial and municipal wastewater facilities to ensure optimal performance of their treatment systems. He is a founder of Aster Bio (www.asterbio.com) specializing in biological waste treatment.
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