Say whether each event belongs to primary treatment or to secondary treatment…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
Say whether each event belongs to primary treatment or to secondary treatment.
- A screen with bars holds back floating debris.
- Soil and small pebbles settle in a chamber.
- Aerobic microbes grow in flocs in a tank into which air is pumped.
- Anaerobic bacteria digest the sludge and give biogas.
- The solids that settle form a sludge, and the liquid above is the effluent.
Need a reminder? The key ideaShow
Sewage is the waste water of a town. Primary treatment is physical: filtration removes floating debris, sedimentation removes grit, and the settled solids are the primary sludge. The liquid above is the effluent. One m³ is L, and mg per litre is g per m³. The mass of a solid in a flow is the flow times its concentration.
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. (a) Primary. The debris is removed by filtration.
Step 2. (b) Primary. The grit is removed by sedimentation.
Step 3. (c) Secondary. Aerobic microbes grow as flocs and use up the organic matter.
Step 4. (d) Secondary. The sludge digesters are the last part of the biological treatment.
Step 5. (e) Primary. This is the primary sludge and the effluent of the primary settling tank.
Answer: (a) primary; (b) primary; (c) secondary; (d) secondary; (e) primary.
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