Lesson 5 ·Class 9 · Waste Generation and Management · Flow Lab
Treating Sewage
What happens between the drain and the river.
Sewage cannot go straight into a river. Follow it through the treatment plant.
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🧹 Step 1 of 7 · Screening
Bar screens hold back rags, plastics and other large floating solids.
Free play — step through the process at your own pace, and move the slider to see what changes. Switch to when you're ready to test yourself.
Physical steps first (screening, settling), then biological ones (aeration, digestion).
What this lesson covers
Challenges to clear
- Advance to the step where bacteria do the cleaning.
- Reach the step that turns waste into biogas.
- Follow the sewage all the way through.
The task
Sewage cannot go straight into a river. Follow it through the treatment plant.
What this lesson covers
- Screening — Bar screens hold back rags, plastics and other large floating solids.
- Grit removal — The flow is slowed so sand, grit and pebbles settle out.
- Primary sedimentation — In settling tanks the heavier organic solids sink as primary sludge and grease is skimmed off the top.
- Aeration — Air is blown through the liquid so aerobic bacteria multiply and consume the dissolved organic matter.
- Secondary settling — The bacterial mass settles out as activated sludge; the clarified water above is much cleaner.
- Sludge digestion — Collected sludge is digested anaerobically, producing biogas and a residue usable as manure.
- Safe discharge — The treated effluent is disinfected and released, or reused for irrigation.
Hint
Physical steps first (screening, settling), then biological ones (aeration, digestion).