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Contaminants in Ground Water
Organic:
• Chlorinated solvents
• Pesticides
• BTX component of gasoline
• MTBE component of gasoline
Inorganic:
• Nitrates (animal waste, fertilizers,
atmospheric deposition, sewage;
form from oxidation of, e.g., NH3)
• Phosphates (detergents, fertilizers,
sewage)
Biological:
• Bacteria (e.g., E. coli)
Treatment of Contaminated Water
For organic contamination:
1) Pump and treat
• Activated charcoal
2) In situ methods
• Reduction of chloroorganics by Fe(s)
3) Bioremediation (anaerobic or aerobic)
• Alkylated benzenes from gasoline
(aerobic)
•PCE, TCE (anaerobic)
For nitrates:
• Denitrifying bacteria in presence of
reducing carbon compound (e.g.,
MeOH) (Expensive)
For phosphates:
• Precipitate as Ca3(PO4)2, Ca5(PO4)3OH
by adding Ca(OH)2
Methods of Disinfection of Water
1) Chlorination
• HOCl
• NaOCl or Ca(OCl)2
Problem: Formation of THMs
(trihalomethanes)
2) Ozone
• Generate on site via electrical
discharge
3) Chlorine dioxide (ClO2·) -- oxidizes organic
matter
• Must generate on site via oxidation of
Na2ClO24) Ultraviolet light (Hg vapor lamps, UV-C)
5) Biofiltration
Typical Method for Treating Water for
Household Use
1) Settling of suspended material
2) Aeration (aids oxidation of readily oxidized
organic matter)
3) Preliminary chlorine treatment (remove
bacteria, other organic material via
oxidation)
4) Remove particulate matter by causing it to
coagulate (via flocculating agent, e.g.
Al2(SO4)3)
5) Add lime to control pH and aid flocculation
6) Final chlorine treatment
7) Can also use activated charcoal, add
fluoride source for dental health (e.g.
Na2SiF6)
Sewage Treatment
Primary treatment:
• Separate large particles via mechanical
screening, then settling
• Solid thus separated is then disposed of
Secondary treatment:
• Biological treatment -- aerobic bacteria
• Sludge from this stage can be used as
fertilizer. Potential problems:
> Pathogens
> Undecomposed toxic organic
compounds
> Toxic heavy metals
• Can use lagoons instead of treatment
Tertiary treatment:
• Can include some or all of a variety of
processes (on next viewgraph)
Techniques for Tertiary Treatment of Water
1) Removing colloidal organic matter by
addition of Al2(SO4)3, filtering
2) Removal of Phosphate (via precipitation as
Ca(PO4)3OH by addition of Ca(OH)2
3) Use of activated charcoal to remove
dissolved organic compounds
4) Removal of heavy metal ions via
precipitation of their (insoluble) hydroxide
or sulfide salts (by adding OH- or S-)
5) Removal of iron by aerating at high pH
6) Reverse osmosis
7) Electrodialysis (like rev. osmosis, but use
electric current to draw ions out of
solution)
8) Ion Exchange (replace H+, OH- with
dissolved species)
9) Partial freezing (pure water freezes out)