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

• Magnesium ions

• Iron ions

Ca+2

Mg+2

Fe+3

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…–calcium bicarbonate

• Also known as scale – white scaly material in pots and pans

Ca(HCO3)2

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•

• precipitates out the ions

• makes calcium carbonate, but…

• not stuck to a pan

• loose pieces that can be rinsed easily!

Na2CO3

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 inCa+2, Mg+2, Fe+3

Water containingNa+1 ion (salt water)

Soft water outNa+1 Hard water ions out

Ca+2, Mg+2, Fe+3