AQA · Chemistry · 8462
GCSE Chemistry (AQA): Waste Water Treatment
Topic 10 — Using Resources. Generated from the caption track of Cognito's lesson video "GCSE Chemistry - Waste Water Treatment - Sources of Waste Water | How to Treat it (2027/28 exams)"; each card deep-links to the moment in the video it came from. Lesson 10.11 of Cognito's AQA GCSE Combined Science (Trilogy) and Chemistry course (Higher tier), filed under AQA Chemistry 8462. Teaching by Cognito — https://cognitoedu.org/coursesubtopic/c2-gcse-aqa-h-c_10.11.
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Why does industrial waste water need extra treatment steps?
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It often contains harmful chemicals (e.g. toxic metals) that domestic sewage treatment does not remove.
What must be removed from domestic and agricultural sewage before disposal?
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Organic matter and harmful microbes, which would otherwise pollute fresh water and pose health risks.
What happens to sewage in a settlement tank?
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Sedimentation: the heaviest solids sink to form sludge, leaving lighter effluent on top.
Name two additional treatments used to remove toxic substances from waste water.
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Adding chemicals to precipitate out metals, and using ultraviolet radiation to break down toxins.
What is the digested sludge remaining after anaerobic digestion used for?
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As a fertiliser, because it is rich in nutrients.
Under what conditions is the effluent digested, and how is this achieved?
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Aerobic conditions — air is pumped into the effluent tank to supply oxygen.
Which gas is produced by anaerobic digestion of sewage sludge?
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Methane, which can be captured and burned as an energy source.
Why is the sludge tank kept sealed during sewage treatment?
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To keep oxygen out so that anaerobic digestion of the organic matter occurs.
What is the first step of sewage treatment?
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Screening — passing the sewage through a mesh to remove large solids such as twigs and plastic bottles.
What are the three main sources of waste water?
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Domestic, agricultural and industrial.
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