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) 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 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

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 - soil - clay - sand - limestone - sandstone - quartz

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

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!

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

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

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

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

Water softeners use ion exchange to remove hard water ions

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