Questions: (See the end of this page for possible pointers / answers / clues).
Question 1
This question is about drinking water and environmental effects.
The government is negotiating with suppliers of drinking water to reduce costs to households. However, these suppliers are also pointing to the fact that it is expensive to produce drinking water from sea water.
a. Explain why it is expensive to produce drinking water from seawater. [2 marks].
b. (i) Explain the possible environmental issues associated with this method of producing drinking water?
(ii) How can these be reduced or eliminated? [4 marks].
Question 2
Compare the ease of treating waste, ground and sea water. [4 marks].
Question 3
Explain why all urban populations need an organised waste water management.
Question 4
Justify why urban populations need a waste water management system compared to small rural area settings. [4 marks]
Question 5
In July 2007, during the summer floods, it was reported that the Mythe Water Treatment works near Tewkesbury became flooded with water from the River Severn. As a result of this, Mythe water treatment works cut off water supplies and, approximately 150,000 people could not access running water in their homes.
a. Explain why it was important for Mythe water treatment works to take such a decision and cut water supply to these homes. (2 marks).
Question 6
The environmental agency carries out regular checks on treated or clean water. Suggest why it is important to do this.
Keywords:
Sewage, waste, anaerobic, aerobic and sedimentation
Learning objective:
To understand how waste water / sewage is treated.
Students target / Outcomes:
Outline the source of waste water / sewage.
Explain how sewage / waste water is treated.
Compare the ease of treating waste, ground and salt water.
Where does waste water / sewage come from?
Daily use of water, through urban lifestyle and industrial processes, results in the production of large quantities of waste water. The three main sources are:
- Domestic
- Agriculture
- Industrial processes.
Sewage is an example of waste water. Sewage includes water from bath, shower, sink, and toilet.
Sewage is waste water and includes water used to flush toilets that contains human waste and toilet paper.
Problem with waste water
Sewage and agricultural waste water require removal of organic matter and harmful microbes.
Sewage is contaminated with human waste (faeces), harmful microbes and toilet paper.
Human waste may cause typhoid and harmful microbes may cause cholera. Waste paper may block the sewage system leading to overflow of sewage into neighbourhoods.
Industrial waste water may require removal of organic matter and harmful chemicals.
The waste water, from industry, may be contaminated with organic matter and harmful chemicals.
………..harmful chemicals to the environment. May kill fish in water bodies.
Agriculture: biggest user of water. : contains organic matter and harmful microbes.
Can cause problems in the ecosystems by having too much nutrient in it. This can lead to eutrophication
Eutrophication is a process whereby water bodies, such as lakes, estuaries, or slow-moving streams receive excess nutrients that stimulate excessive plant growth (algae, nuisance plants weeds).
With the ever growing populations we need to find ways of treating our waste water and sewage in addition to providing enough potable water.
Compared to urban areas, rural areas with small population density tend to have their own individual on site sewage systems called septic tanks. This is not possible in urban areas as space is a premium.
What are the processes / stages involved in the treatment of waste water?
Waste water has to be treated before it is released into our environment
Sewage treatment includes:
- screening and grit removal (removes large solids and grit).
- sedimentation to produce sewage sludge and effluent
(Organic waste settles to bottom (sludge) of sedimentation tanks. Effluent at top passes to aeration tank.
3. aerobic biological treatment of effluent.
Air pumped through, good bacteria kill harmful bacteria in aeration tanks. This is passed into another tank where the sludge, containing good bacteria, sinks to the bottom).
4. anaerobic digestion of sewage sludge (by bacteria).
This produces methane which can be tapped for use in heat and electricity generation. The solid material, produced as a result of anaerobic digestion, can be used as fuel.
Clues to selected questions
Question 1
a. Consider the method used. Does it require use of energy, etc? See suggested approach in question 2 about seawater.
b. (i) Consider the scenario of sourcing electricity from finite resources. What are the pollutants? Carbon dioxide?,
Note: “The combustion of fuels is a major source of atmospheric pollutants. Most fuels, including coal, contain carbon and/or hydrogen and may also contain some sulphur”. (AQA 2016 spec; page 73). Also, greenhouse gases produced as a result of burning fossil fuels to produce energy / electricity (page 71, AQA-8462-SP-2016).
(ii) Alternative energy sources (renewable energy resources such as wind, solar, tidal)
Question 2
Refer to previous notes / sections
Suggested approach
Groundwater:
Relatively easy, can be easily obtained, does not require much treatment.
Wastewater:
Difficult. Contains different types of solid waste and pollutants / harmful microbes. Treatment and removal involves several stages.
Saltwater:
Distilling saltwater is not very difficult. However, energy involved makes it expensive. May be difficult to meet the demand of large populations through this method.
Question 3 (Suggested approach to answer the question)
High population densities, in urban areas, leads to the production of large quantities of waste water and sewage.
Waste water may contain pollutants / harmful microbes / faeces / human waste that need to be treated / removed.
Densely populated areas means little or no space for this to be done locally.
Therefore, organised sewage system designed to treat waste water is needed and located at convenient locations.
Question 4, suggested approach
Compare points in Q3 above to that of rural areas, as explained in the summary on this page.
Question 5, suggested approach: depending on the question
Contamination due to the possible presence of harmful microbes in the water. Needed to check microbes / bacteria levels in the water; treat water;
Health effects: cholera (caused by harmful microbes), typhoid (caused by human waste).
Question 6, suggested approach
To check levels of bacteria / microbes are within acceptable limits.
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