water treatment Flashcards
potable water
water that is safe for humans to drink
what should the levels of substances be in potable water?
-pH-between 6.5 and 8.5
-dissolved salts-low
-microbes/bacteria-none/very low
what does the production of potable water depend on?
the location and type of water available
two types of freshwater in uk, and where are they found?
ground water - found in aquifers underground that trap water
surface water - lakes, rivers, reservoirs
which water dries up first, so what?
surface water so ground water is more commonly used in drier areas
how is potable water produced?
- choose a supply
- filtration: a wire mesh screens out large bits like twigs then gravel and sand beds filter out any other solid bits
- sterilisation: water is sterilised to kill harmful microbes and bacteria by either bubbling chlorine gas, using ozone, or using UV light
why is treating potable water more difficult in dry countries?
there is a lack of surface/ground water so seawater must be treated instead which is more expensive
two types of desalination and explanation
reverse osmosis: salty water is passed through a membrane that only allows H2O molecules through, ions and larger molecules are trapped by the membrane so are separated
distillation: salty water is heated until it boils, leaving dissolved salts behind, travels up tube then condenses back and collected
overarching process name
desalination
problems with desalination
both processes require a lot of energy so is very expensive and impractical for producing large quantities of water
3 types of water
-sea
-fresh
-waste
3 places waste water comes from
-agriculture
-domestic
-industry
why does waste water have to be treated?
to remove organic matter and harmful microbes before it can be put back into freshwater sources as it would cause pollution and pose a health risk if not
waste water acronyms
SSEA, SSSAG
SSEA
screening, sedimentation, effluent, aerobic digestion
SSSAG
screening, sedimentation, sludge, anaerobic digestion, gas
describe the 2 main steps of waste water treatment
- before being treated sewage is screened and passed through mesh to remove large debris and grit
- sewage sits in sediment tank where the heavier suspended solids sink to the bottom to produce sludge and the lighter effluent floats on the top
describe the effluent steps after sedimentation
- effluent is removed from tank and treated by aerobic digestion where air is pumped in to multiply aerobic bacteria digesting the organic matter
- treated water is released back into the environment
describe the sludge steps after sedimentation
- sludge is removed from tank and broken down by bacteria in anaerobic digestion, releasing methane in the process
- methane is used as an energy source
- waste is used as fertiliser
what happens if toxic chemicals are present in waste water treatment?
additional steps are added which include adding chemicals (ozone/chlorine) or UV light
two types of sewage paths
effluent
sludge
which is aerobically digested?
effluent
which is anaerobically digested?
sludge
what does sludge release when anaerobically digested?
methane and biogas
potable v sewage
-sewage requires more processes
-sewage uses less energy than desalination so can be used to make potable water when freshwater is scarce
effluent state of matter
liquid
is potable water pure and why?
no, it contains dissolved substances unlike pure water which just contains H2O molecules
