Chapter 16 Sections 14 Only Fresh Water Resources

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Chapter 16Sections 1-4 OnlyFresh Water Resources
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Hydrologic CycleWater is recycled
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Ground water
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Aquifers need to be protected
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Drinking water Treatment

• Remove solid impurities
• Perhaps soften
• Disinfect

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Remove Impurities
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DisinfectPathogens removed to make water safe
for drinking

• Chlorination
• Ozone
• UV light sources

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ChlorinationAdd reactive chlorine compounds to
water to kill pathogens

• Most common
• Advantages
• Economical
• Residual effects to keep water safe to consumers
  faucet
• Disadvantages
• Safety considerations at treatment facility
• Residual chlorine can have detrimental
  environmental impact

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OzoneAdd reactive ozone, O3, to water to kill
pathogens

• Not as common
• Advantages
• Greatly reduced safety risk at treatment facility
  
• No detrimental environmental impact
• Disadvantages
• Costly
• No residual disinfecting effects to keep water
  disinfected to customer

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UV lightExpose water to UV light to kill
pathogens

• Used by outdoor swimming pools (the sun is the
  source of UV light) in conjunction with
  chlorination
• Advantages
• Minimized exposure to reactive chemicals
• Inexpensive if sun used as UV light source
• Disadvantages
• No residual disinfecting
• Costly if electrically powered UV lamps used

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Fresh water from Salt water

• Distillation
• Reverse Osmosis

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Distillation

• Separate salt from water by allowing water to
  evaporate.
• Boiling point of salt much higher than water
• Salt will remain as solid
• Condense pure water
• Costly due to high energy requirements to heat
  and evaporate water
• Hydrogen bonding
• High specific heat
• High heat of vaporization

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Osmosis

• Water will naturally flow from low concentration
  to high concentration

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Reverse Osmosis

• Water is forced to flow from high concentration
  to low concentration

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Reverse Osmosis
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Biological Role of Osmosis
Hypertonic-crenation Hypotonic-hemolysis
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Hard Water

• Contains Cations
• Ca2
• Mg2
• Fe2
• Interferes with soap action
• Leads to build-up

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Soften water by removing the cations

• Add Sodium Carbonate
• Ion-Exchange
• Precipitation soften with Ca(OH)2

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Carbonate ion attracts cations
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Ion-Exchange Exchanges Na for the hard water
cations
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Ion-Exchange Resin must be Recharged occasionally

• Resin becomes saturated with Ca2, Mg2 and Fe2
• Very concentrated Na water rinsed over resin
• Hard water cations on resin replaced with Na
• Very hard rinse water discarded

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Precipitation Softening

• Chemical reactions to form insoluble compounds
• Insoluble compounds allowed to settle to bottom
  for separation from water