Q 6 How to measure BOD 1 Measure

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. n 2. Incubate the water at 20 o. C in dark n to prevent photosynthesis for 5 days. n 3. Measure the oxygen level again. n 4. The difference between the 2 oxygen level is BOD. n

BOD (Biological oxgen demand) -the amount of oxygen used (0. 5) by organism (0. 5) in a fixed volume of water(0. 5) over a specified period of time (~5 days). n - 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 n

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

Q 11 n (a) Account for the changes in level of n (i) dissolve oxygen n (ii) ammonium compounds n (iii) nitrate compounds n in the river water below the source of pollution.

Q 11 (a) n Sequence of events 1. Point of outfall of sewage (organic matter e. g. urea, protein, dietary fibre + bacteria) Organic pollution

Q 11 (a) n n Sequence of events decomposer (bacteria+fungi) 2. organic matter ------------- ammonium O 2 3. Ammonium -------- nitrite nitrate ammonium nitrate 4. O 2 clean water species + polluted species Nitrate algae