t10- water Flashcards
3 properties of potable water
-drinkable
-isn’t pure- contains impurities
-contains sufficiently low levels of salts+microbes
why is making potable water from fresh water easier than sea water
removing the sodium chloride requires lots of energy
how to make potable water out of fresh water
2 steps
- pass fresh water through filter beds to remove insoluble particles
2.sterilising the water to kill microbes
what are the 2 stages of desalination
-distillation
-reverse osmosis
describe the first stage of desalination
3 points
-distillation
1.sea water is heated until it boils
2.salt remains in flask, water evaporates as steam
3.steam is cooled and condensed to make potable water
describe the second stage of desalination
-reverse osmosis
1.water is put under pressure to pass through a semi-permeable membrane
2.salt can’t pass through membrane, but water can
disadvantages of distillation
-requires lots of energy to boil water and cool steam
-waste water is salty and hard to dispose of sustainably
disadvantages of reverse osmosis
-requires expensive membranes
-lots of waste water
how is human waste in waste water damaging
-contains harmful bacteria
-high levels of nitrogen compounds which can damage aquatic ecosystems
how is industrial waste in waste water damaging
-contains harmful chemicals
how is agricultural waste in waste water damaging
-contains fertilisers/pesticides which ruin sensitive ecosystems
describe the stages of sewage treatment
5 points
1.screening removes large materials from water
2.sewage water undergoes sedimentation. Produces sludge and effluent-good bacteria sinks to the bottom of sludge
3.sludge undergoes anaerobic digestion- it is in a sealed container. Methane is produced and used as an energy source. Waste is used as a fertiliser
4.effluent undergoes aerobic digestion- air is pumped so aerobic bacteria break it down
5. Treated water returns to environment
