Routine microscopic analysis of biological treatment systems provides information that is unavailable through other means. The microscope reveals that bubbling tankful of dark liquid is an amazing habitat teaming with life. By examining the tiniest creatures that inhabit every drop, much can be learned about the treatment environment. You may be unimpressed by the shear numbers of protozoa and metazoa organisms present, typically 4-40 million per gallon. But, the complexity of the single-celled Euplotes patella, with its specialized feeding and locomotion bristles, water cavities, gullet, food pockets, and dual nuclei, will surely grab your interest.
There are many who have a great desire to learn about microorganisms and their roles. This web site is Engitech's attempt to share the wealth of current information, get your feedback, and gather more information. Please comment or question at will.
The following pages are about microorganisms. What they look like, their names, their food, what their presence means, and the water quality they indicate. Updates will appear periodically. The graphics help illustrate each organism's unique role.
The food pyramid graphic depicts a microorganism's position in the food chain. Because energy is lost moving up the food chain, only a few predators are present compared to numerous bacterial feeders. The web, extending into the pyramid shows the microorganism's usual food. Predators typically eat from a narrow set of prey, while omnivores and scavengers eat from a broader food selection. Guess who gets left when food gets scarce. Right, the picky predators disappear first, while scavengers and omnivores survive.
The floc graphic shows where, in relationship to the biomass, the treatment organisms can be found. Bacteria will be part of the floc or present as free cells around the floc. Swimming and gliding ciliates work the open water engulfing bacteria or other prey. Stalked ciliates attach to the biomass and vortex suspended bacteria into their gullets, while crawlers break bacteria loose from the floc surface. Predators feed mostly on stalked and swimming ciliates. The omnivores, such as most rotifers, eat whatever is readily available, while the worms feed on the floc or prey on larger organisms.
The effluent rating graphic is based on the research of Curds and Cockburn.* It is used to predict effluent quality based on the species found in activated sludge. For example, P. aurelia was found only when the effluent BOD was below 10 mg/L. P. trichium, was found 40% of the time at BOD below 10 mg/L, 30% at BOD 11-20, 20% at BOD 21-30, and 10% at BOD > 30. Therefore P. aurelia's presence predicts good effluent quality while P. trichium is not a good indicator of effluent quality because it is found over a wide BOD range.
* "PROTOZOA IN BIOLOGICAL SEWAGE-TREATMENT PROCESSES II. PROTOZOA AS INDICATORS IN THE ACTIVATED- SLUDGE PROCESS." Water Research, 1970, Vol. 4, pp. 237-249.
Microorganisms are directly affected by their treatment environment. Changes in food, dissolved oxygen, temperature, pH, total dissolved solids, sludge age, presence of toxins, and other factors create a dynamic environment for the treatment organisms. Food (organic loading) regulates microorganism numbers, diversity, and species when other factors are not limiting. The relative abundance and occurrence of organisms at different loadings can reveal why some organisms are present in large numbers while others are absent.
This graphic indicates that Opercularia coarctata is not found at very low organic loadings and reaches maximum numbers between food to biomass (F/M) loadings 0.2 and 0.4. This organism would not normally be present in extended aeration plants, but would be found in complete mix, conventional, and contact stabilization plants under normal loadings.
Description: Paramecium is a medium size to large (100-300 m) swimming ciliate, commonly observed in activated sludge, sometimes in abundant numbers. The body is either foot-shaped or cigar-shaped, and somewhat flexible. Paramecium is uniformly ciliated over the entire body surface with longer cilia tufts at the rear of the cell. Paramecium swims with a smooth gliding motion. It may also be seen paired up (conjugating) with another Paramecium which makes a good diagnostic key. The cell has either one or two large water cavities which are also identification tools. This swimmer moves freely in the water column as it engulfs suspended bacteria. It has a large feeding groove used to trap bacteria and form the food cavities that move throughout the body as digestion occurs.
Indicator: Paramecium sp. cover a range of environmental conditions as indicated by the effluent quality ratings shown below for three species. When a particular species occurs in large numbers, significance may be inferred.
Effluent ammonia indicated: 0-20 mg/L
Water quality indicated: variable
Description: Vorticella is a stalked ciliate. There are at least a dozen species found in activated sludge ranging in length from about 30 to 150 m. These organisms are oval to round shaped, have a contractile stalk, a domed feeding zone, and a water vacuole located near the terminal end of the feeding cavity. One organism is found on each stalk except during cell division. After reproducing, the offspring develops a band of swimming cilia and goes off to form its own stalk. The evicted organism is called a "swarmer." Vorticella feeds by producing a vortex with its feeding cilia. The vortex draws bacteria into its gullet. Vorticella's principal food source is suspended bacteria. The contracting stalk provides some mobility to help the organism capture bacteria and avoid predators. The stalk resembles a coiled spring after its rapid contraction.
Indicator: If treatment conditions are bad, for example low DO or toxicity, Vorticella will leave their stalks. Therefore, a bunch of empty stalks indicates poor conditions in an activated sludge system. Vorticella sp. are present when the plant effluent quality is high. A few species, such as V. microstoma, indicate high organic loading and decreasing effluent quality. The species are useful indicator organisms.
Description: Euglypha (70-100 śm) is a shelled (testate) amoeba. Amoebas have jelly-like bodies. Motion occurs by extending a portion of the body (pseudopodia) outward. Shelled amoebas have a rigid covering which is either secreted or built from sand grains or other extraneous materials. The secreted shell of this Euglypha sp. consists of about 150 oval plates. Its spines project backward from the lower half of the shell. Euglypha spines may be single or in groups of two or three. The shell has an opening surrounded by 8-11 plates that resemble shark teeth under very high magnification. The shell of Euglypha is often transparent, allowing the hyaline (watery) body to be seen inside the shell. The pseudopodia extend outward in long, thin, rays when feeding or moving. Euglypha primarily eats bacteria.
Indicator: Shelled amoebas are common in soil, treatment plants, and stream bottoms where decaying organic matter is present. They adapt to a wide range of conditions and therefore are not good indicator organisms. Information is limited regarding the conditions they indicate. Their numbers usually increase with increasing sludge age.
Description: This microscopic animal (200-300 śm) is a typical rotifer. Euchlanis is a swimmer, using its foot and cilia for locomotion. In common with other rotifers, it has a head rimed with cilia, a transparent body, and a foot with two strong swimming toes. The head area, called the "corona," has cilia that beat rhythmically producing a strong current for feeding or swimming. Euchlanis is an omnivore meaning that its varied diet includes detritus, bacteria, and small protozoa. Euchlanis has a glassy shell secreted by its outer skin. The transparent body reveals the brain, stomach, intestines, bladder, and reproductive organs. A characteristic of rotifers is their mastax, which is a jaw-like device that grinds food as it enters the stomach. . At times the action of the mastax resembles the pulsing action of a heart. Rotifers, however, have no circulatory system.
Indicator: Euchlanis is commonly found in activated sludge when effluent quality is good. It requires a continual supply of dissolved oxygen, evidence that aerobic conditions have been sustained.
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