Topic 10 Using Resources Flashcards
What does potable mean?
Safe to drink (contains dissolved substances)
What does pure water mean?
Only contains H2O molecules
What do the methods used to produce potable water depend on?
Available supplies of water and local conditions
What is fresh water?
Doesn’t have much dissolved in it
In the uk what provides fresh water and where does it collect?
Rain, surface water (lakes/rivers) or ground water (rocks that trap water underground)
What are the 2 stages for producing potable water in the uk?
1) Filtration- wire mesh screens out large twigs, gravel and sand beds filter out any other solids
2) sterilisation- kill any harmful bacteria/microbes
What are 3 sterilising agents used for potable water?
Chlorine
Ozone
Ultraviolet light
How is potable water produced if supplies of fresh water are limited?
Desalination of salty/sea water
What are 2 methods of desalinisation?
Distillation
Processes that use membranes such as reverse osmosis
Why are both distillation and reverse osmosis not practical for producing large quantities of fresh water?
Require large amounts of energy- very expensive
How is potable water produced by reverse osmosis?
Salty water passed through membrane, only allows water molecules pass through, ions/larger molecules trapped so separated from water
What does sewage and agricultural waste water require before being put back into fresh water sources?
Removal of organic matter and harmful microbes
Why does industrial waste water have to undergo additional stages of treatment before it is safe to release it into the environment?
Can contain harmful chemicals as well as organic matter
What are the 4 stages of sewage treatment?
Screening and grit removal
Sedimentation, produce sewage sludge and effluent
Anaerobic digestion of sewage sludge
Aerobic biological treatment of effluent
What is the first stage of sewage treatment?
Screening, removal of large bits of material (grit, twigs)
What is the second stage of sewage treatment?
Stand in settlement tank and undergoes sedimentation, heavier suspended solids sink to bottom and produce sludge, lighter effluent floats on top
What is the third stage of sewage treatment?
Sludge broken down by bacteria by anaerobic digestion, releases methane gas
What is the fourth stage of sewage treatment?
Effluent treated, air pumped through water to encourage aerobic bacteria to break down organic matter
What 2 things can the broken down sludge from sewage be used for?
Methane gas - energy source
Digested waste- fertiliser
What are 3 additional stages of treatment for waste water containing toxic substances?
Add chemicals
UV radiation
Using membranes
What is an advantage and disadvantage of sewage treatment?
More processes than treating fresh water
Less energy than desalination of salt water
What are Life Cycle Assessments (LCAs) used to assess?
Environmental impact at every stage of products life
What are the 4 stages of Life Cycle Assessments (LCAs)?
1) Extracting and processing raw materials
2) manufacturing and packaging
3) useful life
4) disposal/end of useful life
Transport + distribution at each stage
Why is producing an LCA not a purely objective process?
Effects of some pollutants hard to give numerical value but require value judgements
What are selective LCAs?
Only show some impacts of product on environment
How can selective LCAs be misused?
Written to deliberately support claims of company for positive advertising
What are NPK fertilisers?
Formulations, contain salts of nitrogen (N), phosphorus (P) and potassium (K)
