PRACTICAL APPLICATION OF MICROBIOLOGY
Section I. MICROBIOLOGY OF WATER AND SEWAGE
a. General. Water is probably man's most precious commodity. Without water,
no living organism can exist. Man's health and comfort are dependent upon a safe and
palatable water supply. Pure water is seldom found in the natural state. Virtually all
water that is available in sufficient quantity for man's needs contains impurities. Most of
these impurities are harmless, although they may affect the appearance and palatability
of the water. Natural occurring water may contain any of the following impurities:
Inorganic chemicals--primarily metals, metallic salts, and gases.
(a) Silt and nonliving organic matter.
(b) Plant life.
b. Plant Life. In addition to the microorganisms previously discussed in this
chapter--viruses, bacteria, and fungi--the plant forms known as algae are of interest to
the sanitary microbiologist. Algae are those microscopic plants--both unicellular and
multicellular--which have chlorophyll but no stems or leaves. They are important in
water microbiology because they impart tastes, odors, colors, and turbidity to water.
c. Animal Life. The animal microorganisms of concern to sanitary
microbiologist are protozoa, rotifers, crustaceans, and helminthes.
(1) Rotifers. Rotifers are among the simplest of multicellular animals. The
rotifer gets its name from two sets of cilia at one end that gives the appearance of two
contra rotating wheels (figure 3-1). The cilia are dual purpose--for mobility and food
catching. The rotifer's chief source of food is bacteria. It is a strict aerobe and is found
only in water that contains low organic content and sufficient dissolved oxygen for
respiration. This is a good indication that the water is low in pollution.
(2) Crustaceans. Most crustaceans, such as crayfish and lobsters, are
macroscopic (visible with the naked eye); however, some are microscopic. Two
crustaceans of interest to the sanitary microbiologist are Daphnia and Cyclops
(figure 3-2). They feed on algae and bacteria and are an important source of food for