Microbes in Human Welfare — Part 2: Sewage treatment and biogas: visual lesson, CBSE Class 12 Biology

Lesson

Microbes clean our water and give us fuel

Part 2 — how microbes treat sewage, and how they produce biogas.

In this lesson you will

Describe primary and secondary treatment of sewage
Explain BOD and how it measures pollution
Describe the production of biogas and the role of methanogens

Diagram

A sewage treatment plant

Treatment happens in two stages: primary (physical) and secondary (biological).

Concept

Primary treatment

Primary treatment is the physical removal of particles. Floating debris is removed by sequential filtration; grit (soil and small pebbles) is removed by sedimentation. The settled solids form primary sludge; the liquid above is the effluent.

Table of the steps of primary sewage treatment
Step	Removes
Filtration	Floating debris
Sedimentation	Grit, soil, small pebbles
Output	Primary sludge (solids) and effluent (liquid)

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