Transcript WATER PURIFICATION

Water Purification
Chemistry
Water Treatment
• Historically (100 years ago) main goal
– Control water-borne diseases, cholera, typhoid
• Potential perils
– Mountain springs flowing through sulfur, zinc,
or arsenic laden rock formations
– Groundwater contamination from fertilizers,
septic tanks, mine tailings
– Harmful bacteria from animals or humans
Water Treatment (Continued)
• Storm drains carry polluted run-off.
• Pollutants from farm drainage or
sewer plants.
• Landfill and waste disposal sites –
rainwater can leach out harmful
substances.
• Homes and factories – corrosive water
can dissolve lead, carry asbestos, etc.
Water Appearance (Turbidity)
• Turbidity
– Clarity of water, once considered an aesthetic
• Possible cause
– Microscopic sized gas bubbles
– Particles suspended in water
– May hide disease causing organisms and allow
them to escape effects of disinfection
• Filtration may remove or reduce
pathogenic micro-organisms
Microbial Disease
• “Raw water” may contain microscopic
parasites from animal fecal contamination
• Includes
– E.coli fecal coliform bacteria
– Giardia, Cryptosporidium and Legionella
– High population densities and outdoor
activities help increase number, dispersion
– Gardia lamblia is common in California’s
Sierra waters. Causes nausea, cramps, diarrhea
in people
Microbial Disease (Continued)
• Since 1984 scientists have linked 11
outbreaks of “cryptosporidiosis” to
local drinking water supplies.
• 1983: Milwaukee – 400,000 people
became ill and 69 people died.
• Several disinfection and filtration
treatments needed to provide effective
protection
Toxic Chemicals
• Trace organic or toxic compounds pose
little or no health risks
• Scientists continually evaluating the effects
of potentially toxic substances to determine
acceptable levels in public water supplies.
• Drinking 1 liter (tap water) has lower risk
– 12 ozs. of beer or 250 mL wine
– One diet cola drink
– One peanut butter sandwich
Natural Water Purification
• In nature…
• Water is naturally purified with 3
steps
• Evaporation, condensation, precipitation
• Bacterial action of the soil
• Filtration through sand and gravel
Water cycle
• Evaporation
– separates water
from impurities
• Condensation
– changes water
from gas to liquid
• Precipitation
– brings water back
to earth for use
Bacterial Action in Soil
• Water moves
through the soil
• Bacteria digest
organic impurities
picked up by the
water
Filtration through sand and gravel
• Layers of the
earth act as
• natural filters for
the water
• removing
impurities as it
drains
Hard water results when
• the water is slightly acidic…
– (pH of 6.0 to 6.5)
• AND…
• It passes through rock containing
slightly soluble minerals
• water picks up these minerals
• Water known as HARD WATER
Hard Water (Continued)
• Hard water contains…
• Calcium ions
+2
Ca
• Magnesium ions
• Iron ions
+2
Mg
+3
Fe
Effects of Hard Water
• Ions react with soap to produce...
Ca+2 + C17H35COONa
Ca(C17H35COO)2 + Na+1
Effects (continued)
• Boiling with hard water
containing bicarbonate ions
creates…
Ca(HCO3)2
–calcium bicarbonate
• Also known as scale
– white scaly material in pots and
pans
Water softening
• Is the process of removing hard
water ions
• we will look at a few different
ways this can be accomplished
Excess soap
• Adding excess soap …
– precipitates all the ions out of solution
• Problems…
– produces excess soap scum
– expensive
Boiling hard water
• Takes all ions out as…
• calcium carbonate (scale)
• Problems…
– produces excess scale
– hard to clean
Add Washing Soda
• Sodium carbonate
•
Na2CO3
•
•
•
•
precipitates out the ions
makes calcium carbonate, but…
not stuck to a pan
loose pieces that can be rinsed easily!
Add phosphates
• Tie up ions into complex molecules
• example would be…
• Calgon
Water Softeners
• Water softeners use ion
exchange to remove hard
water ions
Water Softener
Hard water in
Ca+2, Mg+2, Fe+3
Soft water out
Na+1
Water containing
Na+1 ion
(salt water)
Hard water ions out
Ca+2, Mg+2, Fe+3