Stalked Ciliates: Stalked ciliates feed on the stray bacteria cells. They are easily identified from other ciliates because the main body of the organism is attached to a stalk that is usually implanted in the floc. Stalked ciliates are very efficient feeders and will predominate when the food to microorganism ratio (F:M) is low. They also do best when there are higher dissolved oxygen readings.
Bacteria from an Nitrifying Trickle Filter (NTF) stained with acridene orange. The stain makes DNA appear yellow and RNA appear orange.
Nitrifying bacteria stained with oligo's. The green stain is Nitrobacter, the red, Nitrosomonas.
Rotifers: Rotifers are very large as compared to other organisms. Unlike the protozoa, they are multicellular organisms. The rotifers are only found as the sludge age increases because it takes three days for their eggs to hatch. The principal role of rotifers 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 the foot aids in floc formation.
Filamentous bacteria serve as the backbone of floc formation. Sludge settles most efficiently when it contains a moderate number of filaments which provide structure for the floc and aid in the stripping of the water column. The floc cannot form properly if there are too few filaments, and the floc cannot settle properly if there are too many. The filamentous bacteria are analyzed in two ways: their effect on floc structure and their abundance.
Free-swimming ciliates: Free-swimming ciliates are identified by the cilia that surround most or all of their bodies. Free-swimmers swim faster than flagellates so they can out compete them for food. Free-swimmers are usually found when no large flocs have been formed so that it is easier to swim around.
Nocardia: A filamentous organism that has a hydrophobic (water repellant) waxy nature. Nocardia floats under aeration making it difficult to waste from the system. The foam layer that results entraps other organisms.