You are here: Home » Blog » Knowledge » 23 Commonly Seen Microorganisms In STP


23 Commonly Seen Microorganisms In STP

Views: 1405     Author: Kevin Chen     Publish Time: 2020-06-12      Origin: Site

1. Aspidisca


【Name】 Aspidisca

【Classification】 Activated sludge protozoa

【Size】 Length 25-40µm   Width 18-29µm

Aspidisca 2

【Shape】Small size, round shape. The front is narrow, the end part is wide & straight. It is a little blunt round with convex on the back. It has4 front tactile hairs, 3 belly tactile hairs, and 5 long tactile hairs at the back.

【Lifestyle】Taking bacteria as food, the ecological range is wide, but it is extremely sensitive to chemical substances and can be used as a biological indicator for judging toxic substances. Aspidisca can be used as an indicator of good water quality treatment. When a large number of them appear, the BOD of the treated water is mostly less than 15㎎/l. However, when there are too many Aspidisca - more than 2000/ml. They will be moving in the activated sludge, which will also affect the sedimentation effect of the sludge.

2. Colepidae


【Name】 Colepidae

【Classification】 Activated sludge protozoa

【Size】 Length 55-65µm   Width 28-32µm


【Shape】The body is in the shape of a barrel-shaped grenade, with a little expansion in the middle, and the ratio of body length to body width is about 2 to 1. The shape is fixed and unchanged and the color is brown. Its shell has 15-20 rows, and the shell is divided into six sections by horizontal grooves, and each section forms a certain form and number of "panes". The cilia are evenly distributed throughout the body, with the cell opening at the forefront, which is not easy to see when surrounded by cilia.

【Lifestyle】Colepidae can feed on algae, small flagellates, and small ciliates, as well as dead rotifers. It often occurs when the BOD load is low, the dissolved oxygen concentration is high, or the treated water BOD is low.

3. Stylonychia


【Name】 Stylonychia

【Classification】 Activated sludge protozoa

【Size】 Length 110-120µm Width 45-50µm


【Shape】The shape is oblong, but the two sides are almost parallel, with a depression at the edge of the mouth, the ciliary system has 8 front tentacles, 5 abdominal tentacles, 5 hip tentacles, two hip tentacles are prominent outside the body, the body is very stiff, and the three tail hairs behind are long and firm, with short bristles on the back. The action is inactive, sometimes staying foraging, and the body is full of algae sucked in.

【Lifestyle】It mainly feeds on algae and flagellates, and sometimes eats rotifers. It is not common in activated sludge. The BOD of treated water is usually low when it appears.

4. Euplotes Eurystomus

Euplotes eurystomus2

【Name】 Euplotes Eurystomus

【Classification】 Activated sludge protozoa

【Size】 Length 135-230µm Width 75-98µm

Euplotes eurystomus

【Shape】The body is firm and does not bend or change shape. It is a broad oval with a more or less convex back and flattened ventral surface. The back half is slightly narrower than the front half. The back is rounded and the rim area is quite large and long. There are 7 tentacles, 5 buttocks, 4 tail tentacles, and the telescopic vesicles are located on the right side of the back half. The large nucleus has a long band shape.

【Lifestyle】It mainly feeds on flagellates and ciliates and sometimes devours single-celled algae. It often occurs when the BOD load is low. At this time, the BOD of the treated effluent is usually about 10㎎/l, which is an activated sludge protozoan.

5. Vorticella Micostoma

Vorticella micostoma 2

【Name】 Vorticella Micostoma

【Classification】 Activated sludge protozoa

【Size】 Length 32-70µm Width 22-48µm

Vorticella micostoma

【Shape】The body is approximately circular, but its length usually still significantly exceeds the width. The front port is small and narrow. The enlarged middle is the widest. It gradually tapers from the middle to the front and back ends. It mainly living alone and moves quickly.

【Lifestyle】It takes bacteria as the main food and also preys on microscopic single-cell algae. Its most suitable temperature is 25°C. If it is above 35°C, it will form a package or deformity, and eventually die. A large number will appear when the water quality is good - BOD is mostly below 20㎎/l.

6. Varticella Conrallaria

Varticella conrallaria

【Name】 Varticella Conrallaria

【Classification】 Activated sludge protozoa

【Size】 Length 55-75µm Width 35-58µm

Varticella conrallaria2

【Shape】The figure is long, there are also approximately cylindrical, and a few are relatively rough. The edge of the front is wider than the body. It rarely live alone, like to live together. The body has a thick cylindrical shape and moves quickly.

【Lifestyle】Bacteria are used as food, and sometimes single-cell algae are also eaten. A large number of them appear when the water quality is good. The BOD of the treated water is below 15㎎/l.

7. Carchesium


【Name】 Carchesium

【Classification】 Activated sludge protozoa

【Size】 Length 80-125µm Width 38-60µm


【Shape】The shape is basically the same as that of the Vorticella, the difference is that it has formed a group. Since the branched stem shaft sheath is not continuous but interrupted, each branch can only be stretched separately. The body has a long bell shape, the front section is the widest, and the general length to width ratio is 2:1; the head of the insect body is more or less bent down and suspended.

【Lifestyle】Taking bacteria as the main food, it is generally common in the biological treatment of wastewater and has a clarifying and promoting effect on sewage. When it breeding, the water quality will be good and clean.

8. Epistylis


【Name】 Epistylis

【Classification】 Activated sludge protozoa

【Size】 Length 95-160µm Width 30-40µm


【Shape】The individual is slender or nearly cylindrical, because there is no myofilamentum sheath in the handle, it cannot shrink at all, the body width is about 1/2-1/3 of the body length, the front port is larger, and it has a cilia mouth.

【Lifestyle】Taking bacteria as food. It particularly like eating E. coli, Pseudomonas, etc. In the biological treatment system, it is more present in the bioreactor than in the activated sludge. Generally speaking, when it appears, the BOD of the treated water is quite low.

9. Opercularia Coractata

9 1

【Name】 Opercularia Coractata

【Classification】 Activated sludge protozoa

【Size】 Length 45-56µm Width 19-23µm


【Shape】Compare with Epistylis, the main difference is that its edge of the mouth is straight. And it will never swell to form a "rim lip". Usually the edge of the mouth circumference is notched, and the body is approximately pear-shaped or oval. The central part is significantly enlarged and widest. The front and back ends are more or less thin, and the front port is relatively small in the middle. The outer membrane surrounding the outer substance is very smooth, and there is no visible film pattern.

【Lifestyle】Feeding bacteria as food, especially like Streptococcus edulis, Pseudomonas, Bacillus subtilis, etc. It often appears under the load of 0.2-0.4㎏BOD/㎏MLSS/day and when the treatment water quality is good.

10. Pleuromonas


【Name】 Pleuromonas

【Classification】 Inactivated sludge protozoa

【Size】 Length 6-10µm Width 3-5µm

10 1

【Shape】The body is small, generally kidney-shaped, with rounded ends and 2 flagella. The shorter flagella oscillate endlessly, which is more sensitive to the lack of dissolved oxygen, and makes a quick rotation action when observed under the microscope.

【Lifestyle】It takes bacteria as the main food, and it is suitable for medium-pollution and multi-pollution water. A large number of free bacteria are the basic conditions for their mass reproduction in water, so its large occurrence is often due to high sludge load, sludge disintegration, bacterial micelle decomposition, decreased transparency of treated water quality, and increased COD and BOD indicators.

11. Bodo


【Name】 Bodo

【Classification】 Inactivated sludge protozoa

【Size】 Length 11-15µm Width 5-7µm

11 1

【Shape】The body is small and oval, with a slightly curved "sharp corner" at the front and a rounded back. The two flagella originate from the front end protruding from the cell mouth. Flagella are active organs and food collecting organs, so they are very active.

【Lifestyle】Bacteria are its mainly food. It is a representative of inactive sludge protozoa. It often occurs when the BOD load is high and the dissolved oxygen is low. If it is quantitatively dominant, the treated water is turbid, and most of the BOD is above 30 mg/l.

12. Colepoda


【Name】 Colepoda

【Classification】 Inactivated sludge protozoa

【Size】 Length 32-48µm Width 22-30µm


【Shape】The body is kidney-shaped, the right edge is semi-circularly curved, the rear end is relatively round, and the rear end is thinner when it it hungry, the mouth is located in the middle of the front left edge of the body, and the mouth vestibule forms a shallow depression.

【Lifestyle】The food is mainly bacteria, and Colepoda prefer to eat Escherichia coli  and Serratia marcescens. It often appears under high load conditions - BOD load of about 0.7KG. There are fewer appears when the system operation is stable.

13. Parmecium


【Name】 Parmecium

【Classification】 Inactivated sludge protozoa

【Size】 Length 180-300µm Width 42-75µm


【Shape】Size large, the body is cylindrical, the middle of the back half is the widest, there is a concave groove in the ventral surface of the front half, and there is an oval cell at the bottom of the middle groove. The body is evenly covered with cilia. Some cilia at the back end are a little longer.

【Lifestyle】It mainly take bacteria as food, and the most suitable ecological environment is medium pollution and multi pollution. A large amount appears in an environment where the concentration of dissolved oxygen can hardly be measured, and it appears more frequently in the activated sludge whenever the purification degree is poor.

14. Arcella


【Name】 Arcella

【Classification】 Inactivated sludge protozoa

【Size】 Length 100-150µm Width 50-75µm


【Shape】The surface of its shell is round, and looks like a cover; the side is flat, the abdomen is flat, and the back is very high, so that the entire shell is semicircular; the height of the shell is about half of its diameter. Its color is usually brown or yellow.

【Lifestyle】Arcella feed on flagellates and unicellular algae. Oligo-pollution water is its most suitable living environment. It often appears in large quantities when the activated sludge has a low BOD load and the sludge residence time is too long.

15. Colpidium


【Name】 Colepidium

【Classification】 Inactivated sludge protozoa

【Size】 Length 60-95µm Width 20-25µm


【Shape】The body is oval or approximately long bean-shaped, the back half is often wider than the front half, the ventral surface of the front end turns and makes a slight depression in the front third of the abdomen, and the back end is round.

【Lifestyle】Bacteria is its main food, and it also eats microflagellates; it is found in natural polluted water  and rarely found in oligopolluted water. It is often found in activated sludge with high BOD load and low dissolved oxygen.

16. Metopus


【Name】 Metopus

【Classification】 Inactivated sludge protozoa

【Size】 Length 120-160µm Width 30-60µm


【Shape】Its body is a fusiform shape, the middle abdomen is enlarged. The lip is twisted diagonally toward the ventral surface. Its cilia are sparse around the body, and the arrangement is wide and obvious, with a retractable bubble at the end.

【Lifestyle】Taking bacteria as food, it often occurs in activated sludge that can only detect a small amount of dissolved oxygen. For activated sludge systems, if the number of Metopus is rising, the treatment water quality is mostly turbid and BOD increases.

17. Trachelophyllum


【Name】 Trachelophyllum

【Classification】 Intermediate activated sludge protozoa

【Size】 Length 40-55µm Width 10-14µm


【Shape】The body is long, about 4 times as long as the width. It is spear-shaped or shaped like a needle blade, flat and flexible. The rear end is a little thin and blunt, the cilia are distributed throughout the body, and the endoplasmic body contains many storage granules.

【Lifestyle】Trachelophyllum takes bacteria as the main food and also preys on small protozoa. It mainly occurs in the stage where the activated sludge is in a non-optimal state, which is an important reference for judging whether the activated sludge turns from bad or deteriorates.

18. Amphileptus


【Name】 Amphileptus

【Classification】 Intermediate activated sludge protozoa

【Size】 Length 120-150µm Width 35-45µm


【Shape】The shape of the body is flat, and the front end has a long "neck" that is slightly curved. It has a uniform distribution of cilia throughout the body, with long cilia along the cracked cell. Its body is relatively transparent and the expansion and contraction bubbles are irregularly distributed.

【Lifestyle】It takes ciliates, epistylis, polyps and other ciliates as food. It often appear when the BOD is low, it is an indicator organism to judge whether the water quality is good. But it will consume fixed ciliates that have a clarifying and promoting effect on water quality.

19. Litonotus


【Name】 Litonotus

【Classification】 Intermediate activated sludge protozoa

【Size】 Length 80-110µm Width 14-15µm


【Shape】The body is slender, or lancet-shaped. The widest part is located in the middle, thinning from the middle to the front and back ends; the "neck" is quite long, from one third to two half of the total length.

【Lifestyle】It takes  flagellates and other small ciliates as the main food source; in the natural environment, it is common seen in medium or multi-fouling water, and during system recovery, it often appears in activated sludge.

20. Chilodonella


【Name】 Chilodonella

【Classification】 Intermediate activated sludge protozoa

【Size】 Length 78-250µm Width 36-124µm


【Shape】The body is more transparent and irregularly elliptical, and the back half is wider than the front half; the back is more or less convex, turning slightly to the left to form a sharp corner that is not very protruding; the cell mouth is round on the ventral surface near the front.

【Lifestyle】Taking algae and bacteria as food, the environment adaptability is very strong. It mainly appearing from the deterioration of activated sludge to the recovery period.

21. Etosiphon


【Name】 Etosiphon

【Classification】 Intermediate activated sludge protozoa

【Size】 Length 25-30µm Width 18-22µm


【Shape】The body has a broad oval shape, the front end is straight or slightly depressed, the rear end is round, the dorsal and ventral surface is flat, and the membrane is relatively hard to change its shape; it has 7 or 8 longitudinal grooves; the cell opening is located at the front depression.

【Lifestyle】Etosiphon is likely depend on plant-based saprophytic nutrients for its life. Whether it can swallow the bacteria has not yet been determined. It appears when the BOD is mostly low.

22. Peranema


【Name】 Peranema

【Classification】 Intermediate activated sludge protozoa

【Size】 Length 30-80µm Width 12-28µm


【Shape】The body changes a lot when it is at rest, there is no certain form, it is always long when acting, the rear end is wider and truncated or round; the body tapers from the rear end; a thick flagella extends from the front end, pointing straight ahead during moving.

【Lifestyle】Food sources are relatively wide, bacteria, algae, protozoa, etc. And the ecological environment is also relatively wide. It appears when the BOD load is low and the dissolved oxygen concentration is high.

23. Oxytricha


【Name】 Oxytricha

【Classification】 Intermediate activated sludge protozoa

【Size】 Length 30-156µm Width 54-65µm


【Shape】The body is long and ovate, relatively soft and easy to change, the body length is about 2.5 times the body width, the front is narrow, and then swells backwards, and the ventral surface is flat and the back is more or less convex.

【Lifestyle】Feeds on bacteria, single-cell green algae, and small flagellates; it is highly ecologically tolerant and can tolerate oligopolluting or moderately polluting water; it does not occur much in activated sludge. It appears when the BOD of the treated water is high.

Shanghai CM Environmental Technology Co., Ltd. is a high-tech enterprise specializing in reverse osmosis membrane, ultrafiltration membrane, nanofiltration and MBR membrane assembly, membrane production and sales service, and also a system design and proprietary service provider. 



Shanghai CM Office

 Kaimi : (+86)-18221094035
 No. 1188 Jiangyue Road, Minhang District, Shanghai,China

Authorized distributor in Russia

 (+7) 846 219 21 19
 85,Rabochaya Street, Samara, Russia