A coastal town needs an extra 8000 m3\mathrm{m^{3}}m3 of potable water every day.
The water company considers four options.
| Option | Source of water | Main treatment | Energy needed to make 1 m3\mathrm{m^{3}}m3 of potable water (kWh) |
|---|---|---|---|
| A | ground water from rocks under the town (an aquifer) | filtration and chlorination | 0.4 |
| B | waste water from a sewage works | sedimentation, biological treatment, filtration through membranes and chlorination | 1.5 |
| C | seawater | reverse osmosis | 3.5 |
| D | seawater | distillation | 15 |
The aquifer can safely supply only 2000 m3\mathrm{m^{3}}m3 of water each day. Taking more would cause the level of ground water to fall.
Explain why seawater cannot be made potable by filtration and chlorination alone.
In reverse osmosis, seawater is pumped at high pressure against a membrane.
Explain how this produces potable water.
The water company decides to use option A for as much water as possible and option C for the rest.
Calculate the total energy needed each day to make the extra 8000 m3\mathrm{m^{3}}m3 of potable water.
Evaluate the four options and recommend how the town should get its extra potable water.
Use the information in the table and your own knowledge.
51 exam-style questions on OCR GCSE Chemistry 6.3 Interpreting and interacting with earth systems, covering 6.3.1 Formation and evolution of the atmosphere, 6.3.2 The greenhouse effect and climate change, 6.3.3 Sources and problems of atmospheric pollutants, and 6.3.4 Producing potable water. Each one has a worked solution and a mark scheme showing where the marks go.