1. Water Purification
Chemistry

2. 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

3. 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.

4. Water Appearance (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

5. 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

6. 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

7. 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

8. 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

9. Water cycle condensation evaporation precipitation Evaporation
separates water from impurities
Condensation
changes water from gas to liquid
Precipitation
brings water back to earth for use
condensation
evaporation
precipitation

10. Bacterial Action in Soil
Water moves through the soil
Bacteria digest organic impurities picked up by the water

11. Filtration through sand and gravel
Layers of the earth act as
natural filters for the water
removing impurities as it drains -
soil -
clay -
sand -
limestone -
sandstone -
quartz

12. 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

13. Hard Water (Continued)
Hard water contains…
Calcium ions
Magnesium ions
Iron ions
Ca+2
Mg+2
Fe+3

14. this is also known as soap scum!
Effects of Hard Water
Ions react with soap to produce...
Ca+2 + C17H35COONa
Ca(C17H35COO)2 + Na+1
sodium ions
calcium ions
sodium stearate
calcium stearate
this is also known as soap scum!

15. Effects (continued)
Boiling with hard water containing bicarbonate ions creates…
calcium bicarbonate
Also known as scale
white scaly material in pots and pans
Ca(HCO3)2

16. Water softening Is the process of removing hard water ions
we will look at a few different ways this can be accomplished

17. Excess soap Problems… Adding excess soap …
precipitates all the ions out of solution
Problems…
produces excess soap scum
expensive

18. Boiling hard water Takes all ions out as… Problems…
calcium carbonate (scale)
Problems…
produces excess scale
hard to clean

19. Na2CO3 Add Washing Soda Sodium carbonate precipitates out the ions
makes calcium carbonate, but…
not stuck to a pan
loose pieces that can be rinsed easily!
Na2CO3

20. can only use on a small scale
Add phosphates
Tie up ions into complex molecules
example would be…
Calgon
can only use on a small scale

21. Water softeners use ion exchange to remove hard water ions

22. Water Softener from tank ion exchange resin to house Water containing
Na+1 ion
(salt water)
Hard water in
Ca+2, Mg+2, Fe+3
ion exchange resin
Soft water out
Na+1
Hard water ions out
Ca+2, Mg+2, Fe+3
to house