Chemistry: water treatment

steps of purifying water

1. storage

2. screening

3. flocculation

4. sedimentation

5. sand filltration

6. chlorination + fluoridation

7. underground storage

screening

large debris is filtered out of water collected from dams/ resovoirs

flocculation

aluminium sulphate (flocculationg agents) makes debris stick togetherto form flocs

sedimentation

water moves very slowly through multiple tanks to allow flocculated particles to sink to teh bottom

filtration

water is filtered through a filter bed of sand on top of gravel

additives

chlorine

fluoride

neutrilises the water

if too acid add NaOH

if too basic add H2SO4 or CO2

chlorine

kills bacteria

fluoride

strengthens enamel

dangers of adding too much: chlorine

poisonous, causes digestive upsets

dangers of adding too much: flouride

poisonous, stains teethm, digestive upsets

dangers of adding too much: H2SO4

corrosive, teeth decay

storage

prevents recontamination e.g bird poo, rubbish