Potable water production, sewage treatment, desalination methods.
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CognitoWater treatment and desalination
Key facts & methods
Making water potable (UK — fresh water source)
Potable water is safe to drink. It is NOT pure (contains dissolved minerals — essential for taste and health).
Step 1: Sedimentation — water held in reservoir/settlement tank. Large particles settle.
Step 2: Filtration — water filtered through sand and gravel beds. Removes smaller particles.
Step 3: Chlorination — small amounts of chlorine added. Kills bacteria and other microbes.
UV treatment is an alternative to chlorination.
pH adjustment (lime) may also be used.
Desalination (removing salt from sea water) — fill in the table
Used in water-scarce regions (e.g. Middle East, parts of Australia, California). Two main methods — both are more expensive and energy-intensive than treating fresh water.
Method
How it works
Distillation
Reverse osmosis
Waste water treatment
Sewage treatment works:
Screening: large solids removed by metal grids.
Sedimentation: settled sludge removed. Water enters biological treatment.
Biological treatment: microorganisms break down organic matter in aerated tanks.
Treated water tested and released into rivers. Must meet strict legal standards.
Sludge: dried and used as agricultural fertiliser or for biogas production.
⚡ Show all working — the AI marks against the AQA mark scheme. Method marks awarded for correct working even if the final answer is wrong.
1 markTreatment stepAQA 8462 style
Which treatment step kills bacteria in drinking water?
A Sedimentation
B Filtration through sand and gravel
C Chlorination
D Reverse osmosis
1 markPotable vs pureAQA 8462 style
Why is potable water NOT the same as pure water?
A Potable water contains harmful microbes
B Pure water is unsafe to drink
C Potable water contains dissolved minerals and is safe to drink; pure water contains only H2O
D Potable water is treated with chemicals that make it impure
4 marksCompare desalination methodsAQA 8462 style
Compare distillation and reverse osmosis as methods of desalination. Include how each method works and one advantage and disadvantage of each. (4 marks)
Hint: For each method: explain how it works (1 sentence). Then one advantage and one disadvantage. Be specific.