Water Treatment

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Water Treatment

  1. 1. Water Treatment
  2. 2. PRIMARY POLLUTANTS - ORGANIC POLLUTANTS -
  3. 3. Human waste
  4. 4. Bacteria
  5. 5. Food processing waste - pathogens
  6. 6. PRIMARY POLLUTANTS - INORGANIC POLLUTANTS -
  7. 7. Oil leakage
  8. 8. Acids
  9. 9. Primary Treatment <ul><li>Removes 60% of solid material </li></ul><ul><li>Removes a third of oxygen demanding waste </li></ul><ul><li>1. Water passed through mechanical filters to remove large objects. E.g. paper and condom. </li></ul><ul><li>2. Then passed into grit chamber where sand and small objects settle. </li></ul><ul><li>3. Sedimentation tank where suspended solids settle out as sludge aided by aluminum sulfate and calcium hydroxide. These two chemicals combine to form aluminum hydroxide which precipitates carrying with it suspended dirt particles – Flocculation. Grease is removed and the water is passed on for secondary treatment. </li></ul>
  10. 10. Secondary Treatment <ul><li>Removes up to 90% of oxygen demanding waste such as dangerous bacteria. </li></ul><ul><li>Trickle filters – Degrades waste aerobically using oxygen and bacteria. Organic material is degraded as waste water trickles through a bed of stones. </li></ul><ul><li>Activated sludge process - Waste water is aerated with pure oxygen in a sedimentation tank. </li></ul><ul><li>Water is then disinfected with chlorine or ozone before fit for drinking in a waterway. </li></ul>
  11. 11. Tertiary Treatment <ul><li>Where heavy metal ions, nitrates and phosphates, or residual amounts of organic compounds are removed. </li></ul><ul><li>Precipitation </li></ul><ul><li>– Phosphates removed by aluminium sulfate or calcium oxide. </li></ul><ul><li>– Heavy metal ions removed by insoluble hydroxides or basic salts by addition of calcium hydroxide or sodium carbonate. </li></ul><ul><li>Activated Carbon Beds – Remaining dissolved organic material can be removed by allowing the water to flow down a bed of activated carbon. The carbon is periodically heated to high temperatures to oxidize the organic compounds to carbon dioxide and water. </li></ul><ul><li>Removal of nitrates – Ion exchange columns made of zeolites are used to exchange hydroxide ions for nitrate ions, but this is expensive. Alternatively, anaerobic denitrifying bacteria can reduce the nitrates to nitrogen or the water can be passed through algal ponds where the algae utilize the nitrate as a nutrient. </li></ul>

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