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Potable water treatment
Potable water treatment

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3.5.3 Protozoa

Protozoa are microscopic single cell animals. They utilise solid substances and bacteria as a food source. They can only function aerobically, and in a stream which contains little organic degradable matter they can become a predominant microbial type. They play an important part in sewage treatment where they remove free-swimming bacteria and help to produce a clear effluent.

In an aquatic environment, there are three main types of protozoa:

  1. Those which have an amoeboid structure and move by means of an extruded pseudopod or false foot (e.g. Amoeba).

  2. Those which move by utilising a flagellum or whip-like tail.

  3. Those which move and gather food using hair-like projections (cilia); these can be free-swimming (e.g. Paramecium) or held stationary by means of a stalk (e.g. Vorticella campanula).

Minute multicellular animals which also feed on debris and bacteria are the rotifers (e.g. Keratella), which also play an important part in sewage treatment.