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Organism: Rotifers Identification: The rotifers are the most abundant macro invertebrates found in the activated sludge process. There are about 2000 species, divided into three classes. Most are fresh water species, but there are a few found in marine environments. Rotifers can be found in many different shapes and sizes. Important structural characteristics used to classify rotifers are body shape (sac, spherical or worm), size, number of gonads, foot development, number of toes and protective covering. Most rotifers are colorless, except for the eyespot. However, ingested food may sometimes give the organism the appearance of having color. Rotifers are characterized by the possession of a ciliated area or a funnel-shaped structure at the anterior end that may look like rotating wheels and a specialized pharynx that is part of many pieces that act as jaws. The mouth opening of the rotifer is surrounded by two bands of cilia. The beating of the cilia creates water current for locomotion and food gathering. Rotifers move by swimming freely or crawling. Rotifers are able to consume both microbes and particulate matter. Like protozoa, these microorganisms are strict aerobes and are more sensitive to toxic conditions than bacteria. Rotifers are found usually in a very stable activated-sludge environment in wastewater treatment plants.Rotifers range in size from 40 to 500 µm and have an average life span of 6 to 45 days. They are the smallest animals. Additional Information: Rotifers are metazoa in the phylum Rotifera. They are often in the same size range as ciliates. Most rotifers have a contractile foot that allows them to attach to activated sludge floc. Some types of rotifers include Keratella, Brachionus, Conochilus, and Polyarthra Where Found: They are found in many different types of water, including waste water. They are beneficial in stabilizing organic wastes, stimulating microfloral activity and decomposition, enhancing oxygen penetration, and recycling mineral nutrients. Rotifers are often found in extended aeration systems and systems with a high MCRT. The presence of rotifers in activated sludge generally means a good, stable sludge with plenty of oxygen.The principal role of rotifers in wastewater is the removal of bacteria and the development of floc. Rotifers contribute to the removal of effluent turbidity by removing non-flocculated bacteria. Mucous secreted by rotifers at either the mouth opening or from the foot aids in better floc formation. Rotifers usually are present in older sludge or longer MCRT. Rotifers indicate increasing stabilization of organic wastes and lower BOD and TSS. How to Find Them: Microscopic examination of a wet mount.
More to come soon! Would you like to see a closer look at some of the details of a rotifer or features of his feet or mouth? Check out the Rotifer enlargements at 400x and 1000x and see more fine details. . . . . .
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