potable water and treatment

• what does the process include from fresh water?

  1. filtration - through a wire mesh, and then gravel and sand beds
  2. sterilisation - kills harmful bacteria or microbes
• sea water is treated by desalination which is done by distillation and can also be treated by putting the water through a membrane that only allows water molecules through - reverse osmosis. both use lots of energy so is expensive
• what is the practical to test and distil water in the lab?

  1. test the pH of the water using a pH meter. if its too high neutralise using acid and is its too low add alkali
  2. test for the presence of sodium chloride -> sodium do the flame test should turn yellow if present and chloride ions add dilute nitric acid and silver nitrate solution if present a white precipitate should form
  3. pour the water through a distillation apparatus. heat the flask and will eventually leave dissolved salts behind and the liquid should condense back to liquid
  4. retest the water
• what are the 7 stages of sewage treatment?

  1. screening - removes large pieces of material
  2. sedimentation - the heavier solids sink to the bottom to produce sludge while the lighter effluent floats to the top
  3. the effluent is removed and is treated by biological aerobic digestion
  4. the sludge is also removed and transferred into large tanks. it gets broken down by bacteria - anaerobic digestion
  5. methane gas is produced from this and can be used as an energy source and the remaining waste can be used as a fertiliser
• what is biological aerobic digestion?

  where air is pumped through the water to encourage aerobic bacteria to break down organic matter