AQA · GCSE · Combined Science
Course version: 8464 · Version from Sept 2018
Waste water treatment: Sewage treatment includes:
Sewage treatment is a sequence of physical and biological processes that removes organic matter and harmful microbes from waste water before it is released back into the environment.
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Sewage treatment is a sequence of physical and biological processes that removes organic matter and harmful microbes from waste water before it is released back into the environment. The process begins with screening and grit removal to take out large solids. Next, primary sedimentation allows suspended solids to settle out as sewage sludge, leaving a liquid effluent. The sludge and effluent are then treated differently. The liquid effluent undergoes aerobic biological treatment, where aerobic bacteria break down organic matter and microbes. The sludge is broken down by anaerobic digestion, which reduces its volume and can produce biogas. You must be able to describe these specific stages and explain why waste water requires treatment.
What earns the marks
- State that waste water requires treatment to remove organic matter and harmful microbes before being released into the environment.
- Describe the first stage: screening and grit removal to take out large solid objects.
- Explain sedimentation: suspended solids settle out to produce solid sewage sludge and liquid effluent.
- Describe the treatment of sludge: it undergoes anaerobic digestion by microorganisms.
- Describe the treatment of effluent: it undergoes aerobic biological treatment, where bacteria break down organic matter in the presence of oxygen.
Common mistakes and how to put them right
Confusing the biological treatments.
Put it right by remembering that effluent undergoes aerobic biological treatment, while sludge undergoes anaerobic digestion.
Thinking sewage treatment only removes visible solids.
Put it right: It also removes dissolved organic matter and harmful microbes through biological treatment.
Including sterilisation/chlorination as a standard sewage treatment step.
Put it right: Sterilisation is a step for producing potable water, not standard waste water treatment.
Exam tips
- Clearly distinguish between the treatment of the liquid effluent (aerobic) and the solid sludge (anaerobic).
- Use the correct sequence of stages: screening, sedimentation, then separate biological treatments for sludge and effluent.
Try the lesson
The start of the Waste water treatment: Sewage treatment includes: lesson, made from checked teaching notes for this specification point.
Have a go first
Which process is used in sewage treatment to remove large solid objects such as sticks and plastic?
Listen
Sewage treatment is a sequence of physical and biological processes that removes organic matter and harmful microbes from waste water before it is released back into the environment. The process begins with screening and grit removal to take out large solids. Next, primary sedimentation allows suspended solids to settle out as sewage sludge, leaving a liquid effluent. The sludge and effluent are then treated differently. The liquid effluent undergoes aerobic biological treatment, where aerobic bacteria break down organic matter and microbes. The sludge is broken down by anaerobic digestion, which reduces its volume and can produce biogas. You must be able to describe these specific stages and explain why waste water requires treatment. A strong answer earns marks for these points. State that waste water requires treatment to remove organic matter and harmful microbes before being released into the environment. Describe the first stage: screening and grit removal to take out large solid objects. Explain sedimentation: suspended solids settle out to produce solid sewage sludge and liquid effluent. Describe the treatment of sludge: it undergoes anaerobic digestion by microorganisms. A common slip: Confusing the biological treatments. Instead, remembering that effluent undergoes aerobic biological treatment, while sludge undergoes anaerobic digestion. Exam tip: Clearly distinguish between the treatment of the liquid effluent (aerobic) and the solid sludge (anaerobic).
See it
Key words
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Sedimentation
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Aerobic biological treatment
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Anaerobic digestion
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Waste water treatment
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See every definition
- Sedimentation
- A stage in which suspended solids settle out as sewage sludge, leaving a liquid effluent.
- Aerobic biological treatment
- Treatment of the liquid effluent in which aerobic bacteria break down organic matter and microbes.
- Anaerobic digestion
- Breakdown of the sludge by microorganisms, which reduces its volume and can produce biogas.
- Waste water treatment
- A sequence of physical and biological processes that removes organic matter and harmful microbes before release into the environment.
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