Sewage Treatment
Match each of the terms with the best description.
Each response is used once.

A Settling Tank

B Trickle Filter

C BOD

D Activated Sludge System

E Imhoff Tank

F Floc

1. A particle of organic matter that sinks to the bottom of a
tank. These particles particles consist of little pieces of organic
matter covered with microorganisms. The microbial population of the
particles is a mixed community of bacteria and fungi that degrade
organic compounds and protozoa that eat the smaller microorganisms.
Sometimes alum is added to the sewage, this helps increase the
formation of larger particles that settle out faster.

2. An abbreviation that stands for Biochemical Oxygen Demand.
This is a measure of the total amount of organic matter that is
dissolved in a sewage sample.

3. A principle tool of primary sewage treatment. Lightweight
solids, grease and floating particles are skimmed off the top and
heavier materials sink to the bottom as sludge.

4. A secondary sewage treatment system used in smaller
communities. Effluent from the primary treatment slowly flows
through a shallow artificial stream. The water is oxygenated as it
flows over the rocks. The rocks become covered with a zooglial mass
of aerobic microorganisms that break down organic matter to
CO₂.

5. A secondary sewage treatment system used in larger
communities. Effluent from the primary treatment is seeded with
sludge that contains a high concentration of metabolizing bacteria
and vigorously aerated. Aerobic metabolism breaks down organic
matter that is dissolved in the water to CO₂. Growth of
microorganisms produces more sludge, which is allowed to settle
out.

6. A container for the anaerobic digestion of sludge. Anaerobic
bacteria ferment organic matter producing CO₂,
H₂ and small organic acids such as acetic acid and
formic acid. Then anaerobic archaea convert the small acids,
CO₂ and H₂ to methane.