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Bacterial Contamination

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Bacterial Contamination

In water there are many organisms that are extremely beneficial to man. Bacteria, protozoa and fungi that purify polluted water are essential to our well being. Many of these organisms set into motion the chain reactions that result in purification.

We can classify living organisms in water in many ways and into many groups.

Biologically, there are two major classifications for our purposes. We can classify water organisms either as members of the plant or animal kingdoms.


Under the broad heading of plant forms we can classify the following:


These organisms are found throughout the world. They constitute the chief group of aquatic plants both in sea and fresh water.

Algae range in size from microscopic organisms to giant seaweeds several hundred feet in length. They contain chlorophyll and other pigments which give them a variety of colors. They manufacture their food by photosynthesis.

Algae thrive well in stagnant surface waters, especially during warm weather.

Algae give water fishy, grassy and other even more objectionable odors.

While algae-laden waters are repulsive to man, animals will drink them, and the presence of blue-green algae has been known to cause death of cattle drinking this water.


Diatoms belong to the algae family. Some exists as single cells, others are found as groups or colonies. More than 15,000 forms of diatoms are known to exist.

Diatoms have silica-impregnated cell walls. At times they release essential oils which give water a fishy taste.


Fungi are another large group of plant forms. Like the algae, fungi have many varieties. Including among these are molds and bacteria.

Fungi are not able to manufacture their own food. They exist by feeding on living things or on dead organic matter. Depending on their individual characteristics, they are usually colorless but may vary in this respect.


One important category of fungi is molds. This group of fungi feeds entirely on organic matter. They decompose carbohydrates, such as sugars, starches and fats, as well as proteins and other substances. They thrive ideally in water that has a temperature range of approximately 27 degrees to 38 degrees C. (100 to 187 degrees F.).

The presence of molds is generally a strong indicator of heavy pollution in water.


Bacteria are another important class of fungi. Again numerous smaller groupings are possible. Among the high organisms in this group are the iron, manganese and sulfur bacteria. These higher bacteria gain their energy from the oxidizing of simple inorganic substances.

Lower forms of bacteria can be grouped as those that are helpful and those that are harmful to man. Those harmful to man are mainly the disease-producing organisms.

Helpful organisms hasten the process of decomposing organic waster matter. By feeding on waste material they aid in the purifying of water.

All bacteria are sensitive to the temperature and pH of water. Some bacteria can tolerate acid water, but for the most part they thrive best in water that has a pH between 6.5 to 7.5, that is, essentially neutral water.

As to temperature, most pathogenic or disease bacteria thrive best in water of body temperature. Beyond this no hard and fast statements can be made.

Some bacteria are more resistant to heat than others. Some are more sensitive to cold. At low temperatures, for example, some bacteria may become dormant for long periods of time but will still continue to exist.

Interestingly enough, the waste products of their own growth can hamper bacteria and may even prove toxic to them.

Coliform bacteria can be expected to be present in contaminated water in greater number that is the contaminating organisms.

They are readily identifiable as a result of relatively simple analytical tests.

Bear in mind that Coliform bacteria show that water is contaminated with animal wastes and is possibly contaminated with pathogens. The coliform bacteria are not disease organisms or pathogens in themselves. On the other hand, their absence is no absolute assurance that water does not contain pathogens.


Animal forms like plant life thrive in water providing conditions are right. Among the higher forms of animal life found in water are fish, amphibians, mollusks and anthropoids.

Our concern here is with those lower forms of animal life in water. Again, some are helpful to man as scavengers; others are injurious as possible sources if infection.


There are three types of worms found in water. For the most part they dwell in the bed of material at the bottom of lakes and streams. There they do important work as scavengers.

The rotifers are the only organisms in this category at or near the surface. They live primarily in stagnant fresh water.

The eggs and larvae of various intestinal worms found in man and warm-blooded animals pollute the water at times. They do not generally cause widespread infection for several reasons: they are relatively few in numbers and are so large they can be filtered out of water with comparative ease.


Another basic classification in the animal kingdom is that group of microscopic animals known as protozoa. These one-celled organisms live mainly in water either at or near the surface or at great depth in the oceans.

Many live as parasites in the bodies of men and animals.

Like other organisms, protozoa can be classed as helpful or injurious.

Sometimes drinking water becomes infested with certain protozoa, which is not disease producing. When present, they give the water a fishy taste and odor.

Some protozoa are aerobic; that is, they exist only where free oxygen is available. Some exist where no free oxygen is available. Others can be either aerobic or anaerobic.


Above all else, when a water supply becomes contaminated, correct the problem at once. It is a basic rule of water sanitation to get the source of the problem and eliminate it. If a well, for example, becomes badly contaminated, it is necessary to trace the contamination to its source and, if possible, remedy the situation. It may even be necessary to seek out a new source of supply.

There are a number of ways of chemically disinfecting water. Of these, chlorination is the most widely used. Each method has its advantages. In evaluating them following points should be considered:

  • (a) A disinfectant should be able to destroy all types of pathogens and in whatever number present in the water.
  • (b) A disinfectant should destroy the pathogens within the time available for disinfection.
  • (c) A disinfectant should function properly regardless of any fluctuations in the composition or condition of the water.
  • (d) A disinfectant should function within the temperature range of the water.
  • (e) A disinfectant should not cause the water to become toxic or unpalatable.
  • (f) A disinfectant should be safe and easy to handle.
  • (g) A disinfectant should be such that it is easy to determine its concentration in the water.
  • (h) A disinfectant should provide residual protection against recontamination.

At present, chlorination in one form or another is regarded as the most effective disinfectant available for all general purposes.

Chlorine is normally fed into water with the aid of a chemical feed pump. The first chlorine fed into the water is likely to be consumed in the oxidation of any iron, manganese or hydrogen sulfide present in any supply, including bacteria, if present.

When the “chlorine demand” due to these materials has been satisfied, what’s left over - the chlorine that has not been consumed – remains as a “chlorine residual.”

The rate of feed is normally adjusted with a chemical feed pump to provide a chlorine residual of 0.5 – 1.0 ppm after 20 minutes of contact time. This is enough to kill coliform bacteria but may or may not kill viruses or cysts.

A superchlorination-dechlorination system consists of two basic units. The chlorinator feeds a stepped up chlorine dosage into the water to provide a residual of 3.0 to 5.0 ppm. The dechlorinator (activated carbon filter) then removes the excess chlorine from the water before it reaches the household taps.


Reverse osmosis works through a technique called membrane separation. Raw water enters a module housing the cellulose acetate membrane system. Normal water pressure, or boosted pressure, forces the water against the semi-permeable membrane and only clean water molecules pass through the pores in the membrane. Impurities are rejected and flush away.


Ultraviolet Disinfection will provide water free of microorganisms without the use of germicidal chemicals, oxidants, algaecides, or chemical precipitants. Ultraviolet Disinfection of water employs low-pressure mercury lamps, which generate short-wave ultraviolet, which is lethal to microorganisms including bacteria, protozoa, viruses, molds, yeasts, fungi, nematode eggs, and algae. A UV system consists of an aluminum or stainless steel enclosure, which houses the lamps. The lamps are inter-spaced with teflon tubes through which the water flows and is bombarded by the ultraviolet rays.

The mechanism of disinfection by U.V. irradiation is believed to be a disruption of the DNA and RNA cell replication system by means of the breaking of chemical bonds that tie the individual elements and groups together in these large molecules.

Ultraviolet light can be used with an oxidant such as hydrogen peroxide. When U.V. light splits the molecules of hydrogen peroxide, the OH radicals formed are yet more powerful oxidizers enabling this system to oxidize more types of chemicals.

So.... Do you know what's in your water?

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