I have completed a new training document for operators doing microscopic exam of wastewater. The short course covers the basic bacteria type, protozoa, and other higher life-forms seen in biological waste treatment units. In addition to helping identify the organism, I have provide hints as to their ecology and what promotes their growth in the unit.
Take a look and tell me what you think.
Recently, I was doing a microscopic examination of an industrial activated sludge plant's mixed liquor. Microscopic exams are a very good way to monitor a biological system's overall health. With a simple microscope having 10x and 40x objectives, an operator within 5 minutes can obtain very important information that can reveal: (1) warnings of potential toxic upset, (2) estimate changes in soluble BOD & COD, (3) predict issues with effluent suspended solids (TSS) and turbidity, and (4) determine impact of new influent streams on biomass. Knowledge of any one of these variables is important, but the ability to cover all variables with an easy 5 minute test with no extensive equipment or reagents makes it a double benefit to doing frequent microscopic exams.
When doing a microscopic exam at 100x or 400x magnification, the bacteria do not appear particularly distinctive. In fact, free bacteria are the small round, oval, or rods that appear to be bouncing around in the water. Bacteria in biofilm or floc appear as larger aggregates that should be evaluated for size and density. However, what we usually note in microscopic exams are the protozoa that are associated with the bacteria. The observed protozoa are highly dependent upon water quality which is why frequent use of microscopic exam can establish a baseline and any changes is readily apparent.
The organisms pictured above is a stalk ciliate. This protozoa is found in systems with low soluble BOD, good floc formation that allows for stalk attachment, and sufficient dissolved oxygen. Any toxic shocks will cause stalk ciliates to detach from the floc or disappear completely.
The typical flagellate found in wastwater treatment plants appear as small ovoid shapes that move in the liquid phase surrounded by much smaller free bacteria. Using a single or multiple flagella, long whip-like structures, for motion; these single celled protozoa are one of the first indicator microbes seen in a wastewater treatment system. In the system they consume the free floating bacteria cells and adsorb some soluble organics for their nutritional requirements. (Note: there are some photosynthetic flagellates found usually in ponds, lakes and streams but not as common in wastewater.)
You see flagellates at the early stages of wastewater treatment or when there is log phase growth of bacteria. In lagoon systems, you will often find flagellates predominating near the inlet where dissolved oxygen is low & soluble BOD high. If seen near the effluent, this indicates some type of upset condition. Common triggers include - (1) high hydraulic loads, (2) increased organic loadings, (3) pond turnover, and (4) problems with dissolved oxygen concentrations.
In activated sludge or fixed film systems, the sudden appearance of flagellates can indicate an increase in organic loadings or follow a toxic event that killed off significant portion of the living bacteria found in the MLVSS or biofilm. Either event merits further investigation into what is causing the increase in flagellate populations.
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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