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Contaminants in Ground Water

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., NH 3 )

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Contaminants in Ground Water

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  1. 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)

  2. 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

  3. 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 Na2ClO2- 4) Ultraviolet light (Hg vapor lamps, UV-C) 5) Biofiltration

  4. 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)

  5. 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)

  6. 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)

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