4.10.1 Using the Earth’s resources & obtaining potable water

• Humans use the Earth’s resources to provide:

  • Warmth
  • Shelter
  • Food
  • Transport
• Natural resources are supplemented by agriculture, which provides:

  • Food
  • Timber (woods for building)
  • Fuels
  • Clothing
• Finite resources are resources that are limited in supply and cannot be replaced at the same rate as it is used/ removed from the environment (cannot be replenished)
• Finite resources are found at:

  • The Earth’s crust
  • Oceans
  • Atmosphere
• Finite resources are used to provide:

  • Energy
  • Useful materials
• Chemistry plays an important role in improving agriculture and industrial processes to provide new products and in sustainable development
• What is sustainable development?


  Development that meets the needs of current generations without compromising the ability of future generations to meet their own needs
• What is potable water?

  • Water that is safe to drink
  • With sufficiently low levels of dissolved salts and microbes
  • pH 6.5-8
  • NOT ‘pure water’
• The methods used to produce potable water depend on available supplies of water and local conditions
• In the UK, rain provides fresh water (water with low levels of dissolved substances), which collects in the ground and in lakes & rivers
• Most potable water is produced by:

  • choosing an appropriate source of fresh water
  • passing the water through filter beds
  • sterilising
• How to sterilise the water?

  Use sterilising agents:

  • Ozone
  • Chlorine
  • Ultraviolet light (UV light)
• If fresh water supply is scarce (limited), desalination of salty water (sea water) may be required
• Why we usually use fresh water to produce potable water but not with salty water?

  More purification processes are needed:

  • Desalination
  • Distillation
  • Reverse osmosis

  ->which require large amounts of energy
• What are the main sources of the production of wastewater?

  • Urban lifestyles
  • Industrial processes
• Waste water has to be treated before releasing into the environment as it may damage the aquatic ecosystem
• Sewage and agricultural waste water require removal of organic matter (fertilisers) and harmful microbes
• Industrial waste water may require removal of organic matter and harmful chemicals
• Describe the sewage treatment?

  • Screening through a mesh and grit removal->remove large particles
  • Sedimentation allows tiny particles to settle out from still water, which produces sewage sludge & effluent (liquid remains on top)
  • Anaerobic bacteria digest sewage sludge
  • Aerobic biological treatment of effluent (use aerobic bacteria to reduce the volume of solid waste)
• Anaerobic bacteria in waste water treatment:

  • Produce biogas (can be burnt for electricity)
  • Digested sludge can be used as fertilisers (farming)
• Aerobic bacteria in waste water treatment:

  • Digest and lower the levels of organic molecules and harmful microorganisms
  • Aerobic condition: air is bubbled through the liquid effluent->allows aerobic bacteria to multiply
  • Liquid effluent can then be safely discharged into nearby rivers/ the sea
• Evaluate the 3 main ways of making potable water.

  Fresh water (rainwater)

  ->found in lakes, rivers and in rocks underground

  ->low levels of dissolved salts and microbes

  ->aquifers can sometimes be polluted (eg by fertilisers)

  Salt water

  ->large amount available

  ->very high level of dissolved salts

  ->desalination is needed (require large amounts of energy)

  Sewage (waste water)

  ->can also produce biogas which can be burnt to generate electricity

  ->many purification steps are needed
• The Earth’s resources of metal ores are limited (finite)
• Name 2 ways of extracting copper from low-grade ores.

  • Phytomining
  • Bioleaching
• What are the advantages of using phytomining and bioleaching?

  Avoid traditional methods:

  • digging, moving & disposing large amounts of rock
• What is phytoming?

  • uses plants to absorb metal (copper) compounds
  • harvest and burn the plants to produce ash that contains metal compounds
  • extract the metal from the ash
• What is bioleaching?

  • put bacteria solution into old mines
  • bacteria digest the rocks and produce a liquid (leachate) which contains metal compounds
• Metal compounds can be processed to obtain the metal (eg displacement reaction & electrolysis)
• Why did the development of the Haber process allow the global population to increase?

  synthetic fertilisers (ammonia) allowed intensive farming, producing more food
• Making potable water in the UK

  Water source: rainwater (fresh water)

  ->passing through filter beds (remove insoluble particles)

  ->sterilising the water to kill microbes (chlorine, ozone, UV light)
• Desalination

  using sea water to make potable water
• Examples of desalination

  distillation

  reverse osmosis
• Distillation

  ->heat the sea water until it boils

  ->condense steam to make potable water

  ->requires a lot of energy to boil the water and cool down the steam

  ->waste water is very salty and difficult to dispose of in a sustainable way (not harming the marine ecosystems)
• Reverse osmosis

  ->water is put under high pressure

  ->pass through a membrane with tiny pores in it

  ->pores allow water molecules through

  ->most ions and molecules cannot pass through

  ->require expensive membranes

  ->low efficiency (large volume of waste water)
• Examples of waste water

  ->human waste (harmful bacteria, high level of nitrogen compounds —> harm aquatic ecosystems)

  ->industrial waste water (harmful chemicals, toxic metal compounds)

  ->agricultural waste water (fertilisers, pesticides —>disrupt sensitive ecosystems)
• Sewage treatment

  ->screening & grit removal (remove large particles)

  ->sedimentation (settle out tiny particles)

  ->sewage sludge (anaerobic digestion by specific bacteria)

  ->liquid effluent (aerobic digestion by bacteria, reduce volume of solid waste)