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Water Pollution

Water Pollution. Causes of water pollution. Livestock waste Oil spillages Residues of pesticides Detergents in sewage Industrial effluents. Livestock waste.

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Water Pollution

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  1. Water Pollution

  2. Causes of water pollution • Livestock waste • Oil spillages • Residues of pesticides • Detergents in sewage • Industrial effluents

  3. Livestock waste When there is an excessive amount of organic matter discharged into water, the existing micro-organisms will grow and multiply rapidly. Oxygen is depleted rapidly. Anaerobic micro-organisms begin to break down partially the organic matter releasing toxic gases like CH4 , NH3 and H2S. The aquatic organisms will die.

  4. Oil spillages Oil clogs the feathers of sea birds and kills marine life. On beaches, oil drives away holiday-makers and spoils recreation resorts.

  5. Residues of pasticides Pesticides cause immediate toxic effects on aquatic life or may accumulate along the food chain until a toxic level is reached. DDT was previously used and banned in many parts of the world including Hong Kong.

  6. Detergents Red tides brought about by phosphates in some detergents. Foaming in rivers and lakes.

  7. Industrial effluents Vary with the industry involved. May contain Cd, Cr, Cu, Hg, Ni, Pb, Zn, cyanides, polychlorinated hydrocarbons.

  8. Dissolved oxygen (DO) • As an indicator of oxygen content in water. • Measured in mg / dm3 or % saturation e.g. Max. conc. = 10 mg dm-3 at 16oC, if a water sample contains 6 mg dm-3 , the % saturation of DO is 60%. • Fishes normally require 4-6 mg dm-3 for survival.

  9. Biological oxygen demand(BOD) • The amount of oxygen required to break down the organic matter present in a water sample. • Five-day BOD, (BOD5) • A sample has an initial DO of 8 mg dm-3 drops to 2 mg dm-3 in 5 days, BOD5 = 6 mg dm-3 • Natural clean water has a BOD5 of about 1 to 4 mg dm-3

  10. Measures to improve water quality • Sewage treatment • Only part of the wastewater receives some sort of treatment before discharge. • The treatment processes include • Primary treatment :screening, sedimentation • Secondary treatment: digestion of pollutants by micro-organisms. • In 1995, 5 major secondary treatment plants in H.K., treat 20-25% of the total sewage.

  11. Measures to improve water quality Chemical Waste Treatment Centre(CWTC) • Physical methods • Chemical methods • Neutralization of acids and bases • Precipitation reactions • Reduction reactions • Incineration

  12. Sewage Treatment link

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