En anglais

Turning river water into drinking water

Science · Matter & Materials · ages 15-16

Name ______________________ Date ____________

What is the purpose of chlorination in the river-water example?
- Removing large branches
- Removing suspended silt
- Inactivating many germs
A river-water plant removes large debris before settling. It filters the water after settling and chlorinates only after filtration. Which order fits?
- Filter, chlorinate, screen, settle
- Screen, settle, filter, chlorinate
- Settle, screen, chlorinate, filter
Potable water must contain only water and no dissolved minerals.
Circle one: True False
Which sewage treatment stage can produce biogas containing methane?
- Screens that separate large rubbish from sewage
- Aerated tanks that supply oxygen to the liquid waste
- Anaerobic digesters that treat separated sludge
Which action uses energy to separate water from dissolved salts in reverse osmosis?
- Heating seawater and condensing its water vapour
- Pumping water through a membrane under pressure
- Filtering seawater through sand to trap suspended particles
Wastewater contains suspended silt and dissolved organic waste. Which pair of steps addresses these in the lesson's example?
- Settling removes silt; aerobic microbes break down organic waste
- Screens remove silt; settling breaks down organic waste
- Aeration filters out silt; settling removes all dissolved organic waste
Aerobic liquid-treatment tanks work without oxygen, while anaerobic sludge digesters need a supply of oxygen.
Circle one: True False
A coastal town has an adequate fresh-water supply. A student recommends desalination only because seawater is plentiful. What is missing from the argument?
- A comparison of energy costs and available water supplies
- A comparison of how clear the two supplies look
- A guarantee that an ordinary sand filter removes every dissolved salt

Answer key

For grown-ups. Fold this page away before handing over the rest.

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Inactivating many germs · Chlorine is used for disinfection. It inactivates many microbes, but it is not equally effective against every pathogen.
Screen, settle, filter, chlorinate · Screening removes large debris before settling. Filtration follows settling, and chlorination follows filtration, so the order is screen, settle, filter, chlorinate.
False · Potable means safe to drink. Dissolved minerals can remain without making it unsafe.
Anaerobic digesters that treat separated sludge · Anaerobic sludge digestion works without oxygen and can produce biogas containing methane.
Pumping water through a membrane under pressure · Reverse osmosis uses pressure to move water through a membrane while most salts stay behind.
Settling removes silt; aerobic microbes break down organic waste · Settling separates suspended solids. Microbes supplied with oxygen break down organic waste remaining in the liquid.
False · The oxygen requirements are reversed. Aerobic treatment uses oxygen; anaerobic digestion works without it.
A comparison of energy costs and available water supplies · A plentiful source alone does not settle the choice. Desalination needs energy, and the town has another supply to compare.