Practise 22 exam-style questions on Waste water treatment for AQA GCSE Chemistry. Write your answer as you would in the exam and get it marked in seconds against the mark scheme, point by point, with an AI tutor on hand if you get stuck.
22 questions
1–6 marks each
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20 questions, marked as you go
Sample questions with model answers
Here are 4 of the questions in this topic, each with a model answer, an explanation of why it earns the marks and the mark scheme an examiner would use.
Question 1
1 mark
Write these three stages of sewage treatment in the order in which they happen.
aerobic treatment of effluent screening and grit removal sedimentation
Model answer
Screening and grit removal, sedimentation, aerobic treatment of effluent.
Explanation
Large objects and grit are removed first, then sedimentation separates sludge from effluent, and only then is the effluent treated with aerobic bacteria.
Mark scheme
1 mark
screening and grit removal, then sedimentation, then aerobic treatment of effluent
all three in the correct order for the mark
Question 2
2 marks
Anaerobic digestion of sewage sludge takes place in sealed tanks.
Suggest two reasons why the tanks are sealed.
Model answer
The tanks are sealed to keep oxygen out, because the bacteria must work in anaerobic conditions. Sealing also allows the methane produced to be collected and used as a fuel.
Explanation
The bacteria that digest the sludge work without oxygen and produce methane. Collecting the methane provides energy and stops a powerful greenhouse gas escaping.
Mark scheme
1 mark
to keep oxygen / air out (anaerobic conditions are needed)
max 2
1 mark
to collect the methane / biogas produced, to use as a fuel
1 mark
to stop methane (a greenhouse gas) or smells escaping into the air
Question 3
3 marks
Describe the anaerobic digestion of sewage sludge.
Model answer
The sludge is put into sealed tanks where bacteria break down the organic matter in the absence of oxygen. This produces methane (biogas), which can be burned as a fuel, and the digested sludge that remains can be used as a fertiliser.
Explanation
Anaerobic means without oxygen. Anaerobic bacteria break down the sludge and produce methane, so sewage treatment can generate some of its own energy.
Mark scheme
1 mark
the sludge is broken down by bacteria / microorganisms
max 3
1 mark
in the absence of oxygen
allow in sealed tanks without air
1 mark
producing methane / biogas, which can be used as a fuel
1 mark
the remaining digested sludge can be used as a fertiliser
Question 4
4 marks
Comment on the relative ease of obtaining potable water from ground water, waste water and salt water.
Model answer
Ground water is the easiest source because it has low levels of dissolved substances and only needs filtering and sterilising. Waste water is harder because it contains organic matter and harmful microbes, so it needs many more treatment stages before it is safe to drink. Salt water is usually the most difficult because it must be desalinated by distillation or reverse osmosis, which require large amounts of energy and are expensive.
Explanation
The ease depends on what must be removed. Solids and microbes are relatively easy to remove; organic matter needs several stages; dissolved salts need energy-intensive desalination.
Mark scheme
1 mark
ground water is easiest: it has low levels of dissolved substances, so only filtering and sterilising are needed
max 4
1 mark
waste water needs many more treatment stages (screening, sedimentation, biological treatment) before it can be made potable
1 mark
salt water needs desalination (distillation or reverse osmosis)
1 mark
desalination requires large amounts of energy, so it is usually the most difficult / expensive
1 mark
treating waste water usually needs less energy than desalination
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