Photo gallery of microfauna of activated sludge

Consumers (protozoa and micrometazoa) are biotic components of activated sludge systems. Due to the fact their power is based on dispersed bacteria and other microorganisms they are responsible for clarifying and lower the toxicity of the final effluent. Predation and competition are existing relationship in this type of system, and until a stable dynamic is reached, various oscillations and successions in the population may occur and are linked to the sludge age (SA), nitrification, relation food/microorganism (F/M) and dissolved oxygen (DO).

The identification and quantification of microorganisms is a very useful tool to indicate the process development as well as its efficiency. Thinking about it, Genética Environmental Technologies in addition to offering the identification and quantification in the reports of aerobic microscopy also offers an online album. Browsing through this album you will know, through micrographic images performed in our microscopy sector, the main protozoa and micrometazoa. that are part of this very special ecosystem that is the activated sludge as well as its main characteristics and the role played in the system.

The consumers of activated sludge microfauna are divided into two large groups, simply select the column next to the group of interest and learn more about your specimens:

Ciliates

The ciliates are unicellular microorganisms that have the highest degree of structural complexity. They have as a means of locomotion the cilia, which are short and numerous organelles, protruding from the wall of the cell and performing coordinated rhythmic beats. In addition to the locomotion, the eyelashes are also useful for the capture of organic particles as food and bacteria, thereby clarifying the effluent. Ciliates are subdivided into four groups:

Free Swimming Ciliates

Are protozoa that have eyelashes evenly distributed throughout the outer surface of the body and swim freely among the flakes. Because they are fast and spend much energy to move, they require large amounts of food, and for this reason, are often associated with high organic load and low OD effluent and may ingest more than 500 bacteria per hour.

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Predators of Flakes Ciliates

They are flattened dorsoventrally microorganisms that crawl around the biological flakes, scraping the surface of bacteria clusters with organic materials, ingesting flakes fragments and thereby contributing to the rounded appearance of an ideal flake. The cilia are modified and grouped in the part that is in contact with the substrate, forming "little legs" with which they move on the flake surface. Its prevalence in a system indicates nitrification and good operation of the plant with well formed flakes or in process phase.

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Fixed Ciliates

Also called stalked ciliates, are microorganisms that adhere to the substrate via a stalk and the eyelashes are found in the anterior region, near the mouth. Because of this adhesion they spend little energy and survive in low amount of food. They live in colonies or isolated which can form branched stems and look like small trees. In some genres, like Vorticella sp., The stalk is retractable and takes its name from myoneme, allowing the ciliated escape from predators through its rapid retraction. When in colonies indicates good system efficiency and DO residual, when individual one must check the balance of protozoa, because it may indicate poor effluent quality.

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Carnivorous Ciliates

Also known as suctoria, these microorganisms transform the eyelashes in structures similar to spines located at the vertex. On the approach of a prey, these hard tentacles prick the cell and feed on its contents. In adult stage live attached to the biological floc through a stalk, and when young have free life. In activated sludge systems indicate stability and high DO due to the fact that they are very sensitive to operating changes.

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Flagellates

They are protozoa which move around through an organelle in the form of a thin elongated filament, usually located on the front part of the body, called flagellum. They feed mostly of nutrients dissolved in wastewater, but can ingest algae and bacteria. Most activated sludge samples are small and run a wave motion, being found in wastewater of aeration deficiency, poor clearance, cargo shock or toxicity. Occasionally, flagellates may be found in high concentrations in old sludge, feeding on the micrometazoa in the process of decomposition, such as rotifers and annelids. Under adverse conditions the flagellum can get loose from the body, however, regeneration is instantaneous.

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Amoebae

The amoeba is a unicellular microorganism, or consists of only a single cell. One of its main features are the body extensions, called pseudopodia, responsible for moving and getting food. The pseudopodia are formed from a movement of the internal fluid of the cell (endoplasm) what causes a projection within the cell. Its shape is very variable, since its gelatinous body takes different forms in some cases. Some species have a protective shell and due to the presence or absence of it amoebas are subdivided into two groups:

Naked amoebae

They are microorganisms that move around through transitional organelles, known as pseudopods (pseudo=false; pods=feet), constituted by simple protoplasmic extensions that occur in any part of the body and assist in feeding, locomotion and phagocytosis. They are generally transparent and have no defined way, but when seen in star-shaped, indicate the stress suffered due to the manipulation of the sample in which they are. Because they do not compete for food, they only prevail in environments where it is offered in large quantities, as in the beginning of operation of an activated sludge system, and due to this fact are associated with bad clearance conditions. However, some genres are often seen in good quality systems.

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Thecamoebians

They are amoebae that have a protective shell called theca, which can be secreted by itself or be formed by amoeba particles removed from the medium, calcareous, siliceous or organic. The thecamoebians are able to compete with other microorganisms only when the food is plentiful (high F/M), as in the beginning of the operation of an activated sludge system. In older sludge thecamoebians indicate a nitrified wastewater with low ammonia concentration.

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Rotifers

Micrometazoa more often found in activated sludge systems. They feed on bacteria, organic debris, small flagellates, ciliates and even other micrometazoa, and thereby clean the effluent lowering the turbidity. On the other hand rotifers are food for some worms. They are free lonely living microorganisms but some species may live in colonies or sessile. Its elongated and generally cylindrical body has cilia in the cephalic, that assist in food and transportation. Their presence is usually an indicator of good system efficiency due to it being associated with elevated sludge age and sludge in high oxidation stage.

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Annelids

They are segmented worms with the body formed by rings (from Latin annelus = rings), being among the largest micrometazoa of activated sludge. The easy adaptation allows them to inhabit a wide variety of ecological niches, feeding mainly on algae and other invertebrates. They have high regenerative capacity and a genre in particular (Aeolosoma sp.) The presence of orange glands in the skin can alter the color of the effluent, when they are found in large numbers. Occur only in stabilized sludge with excess of dissolved oxygen and high sludge age. It is rare and slightly dominant.

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Nematodes

They are elongated and cylindrical worms with generally tapered ends, with no trace of segmentation throughout the body. Move through rapid contractions of the body in the shape of "S" and are usually colorless, inhabiting the bottom sludge. They feed of particulate material and micro-organisms such as protozoa, other nematodes, rotifers and tardigrades. Are seen more often in biological contactors and aerated biofilters, where the flakes stick, leaving visible holes, are resistant to extreme temperatures and lower dissolved oxygen concentrations. They may indicate mixture of considerable concentration of sewage with industrial effluent. In activated sludge systems they  rarely appear, indicating tendency to high sludge age.

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Tardigrades

These micrometazoários, are popularly known as "water bears" and are rarely seen in the extended aeration systems, which feed on the cell contents of nematodes, rotifers and protozoa, and some kinds of algae. ts body is short, plump and on the abdomen shows four pairs of stubby legs, which serve for locomotion. They are affected by small concentrations of ammonia, being completely nitrified effluent indicators.

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