Phase contrast is preferable to bright field microscopy when high magnifications (400x, 1000x) are needed or the specimen is colorless or the details so fine that color does not show up well. Cilia and flagella, for example, are nearly invisible in bright field but show up in sharp contrast in phase contrast. Amoebae look like vague outlines in bright field, but show a great deal of detail in phase. Most living microscopic organisms are much more obvious in phase contrast.

It is the excess cellular mass of these organisms produced during the treatment of wastewater that makes up the "bio" of biosolids.

Photographs provided courtesy of the late Ronald Corner, Former Laboratory Manager, City of Cadillac Wastewater Treatment Plant.

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