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Q 6. How to measure BOD?

Q 6. How to measure BOD?. 1. Measure the volume of a sample of water in a dark bottle. Measure its oxygen level by oxygen meter / chemical method. 2. Incubate the water at 20 oC in dark to prevent photosynthesis for 5 days. 3. Measure the oxygen level again.

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Q 6. How to measure BOD?

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  1. Q 6. How to measure BOD? • 1. Measure the volume of a sample of water in a dark bottle. Measure its oxygen level by oxygen meter / chemical method. • 2. Incubate the water at 20 oC in dark • to prevent photosynthesis for 5 days. • 3. Measure the oxygen level again. • 4. The difference between the 2 oxygen level is BOD.

  2. BOD (Biological oxgen demand) • -the amount of oxygen used (0.5) by organism (0.5) in a fixed volume ofwater(0.5) over a specified period of time (~5 days). • - indicate the amount of organic matter and microorganisms  indicate the degree of water pollution BOD high  degree of pollution high BOD low  degree of pollution low  clean water

  3. Tubifex worms / blood worms • - can tolerate to low oxygen level • - indicator species of polluted and anoxic water Mayfly nymph / dragonfly nymph • - cannot tolerate to low oxygen level • - indicator species of clean water with high oxygen level

  4. Q11 • (a) Account for the changes in level of • (i) dissolve oxygen • (ii) ammonium compounds • (iii) nitrate compounds • in the river water below the source of pollution.

  5. Q11 (a) • Sequence of events 1. Point of outfall of sewage (organic matter e.g. urea, protein, dietary fibre + bacteria)  Organic pollution

  6. Q11 (a) • Sequence of events • decomposer (bacteria+fungi) 2. organic matter ------------------------- ammonium O2 3. Ammonium --------------- nitrite  nitrate ammonium nitrate 4. O2 clean water species + polluted species Nitrate  algae

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