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Biochemical oxygen demand(bod)


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Masud alam Ansari

Published in: Environment
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Biochemical oxygen demand(bod)

  1. 1. Biochemical oxygen demand(BOD) & Chemical oxygen demand(COD)
  2. 2.  What is B.O.D. ? - Amount of oxygen required for bacteria to decompose organic matter. ( Biodegradable ) Why we go for the testing of B.O.D. in sewage ? - To determine what effect dirty water and how much bacteria and organic matter present in the sewage .
  3. 3. What will happen if sewage have high B.O.D. ? - Then sewage will be in anaerobic condition. Why B.O.D. is usually lesser than C.O.D. ? -Because the bacteria present in sewage is only responsible for decompose the biodegradable matter. In normal sewage B.O.D. is two-third of C.O.D.
  4. 4. Stage of Decomposition of Organic matter - 1st stage :-In 1st stage the carbonaceous matter are oxidized. The B.O.D. of sewage for this stage is about 90 % of total B.O.D. - 2nd stage :- In the 2nd stage the oxidation of nitrogenous matter take place . It contain protein, fats , amino acids etc.
  5. 5. Why we are taking 5 days when performing B.O.D. test ? - Because 70% to 80% of organic matter will be oxidized with in 5 days. In India people developed this BOD test at 27 C in 3 days . Limitation of BOD test 1) It is not prefer for industrial sewage . 2) Time duration of the test is 5 days. 3) pre-treatment is needed if the sample contain toxic waste. 4) It is essential to have high concentration of active bacteria .
  6. 6. Some facts related to B.O.D. -Oxidant is microorganism. -For drinking water B.O.D. is less than 1mg/l. -D.O. should at least 4mg/l at time of disposal. -Any to be discharged in natural bodies of water should have BOD less than 20 mg/l.
  7. 7. B.O.D. curve
  8. 8. What is C.O.D. ? - Amount of oxygen required to chemically oxidize both matter to water and carbon dioxide. Why we go for COD test ? - It take less time to perform the test as compare to BOD test. Why COD is called theoretical demand ? -It is impossible to know the detail of organic compound present in the sewage so, that it called theoretical demand.
  9. 9. which chemical oxidizing agent is used for COD test ? Why - Potassium dichromate . -Cheap. -Completely oxidize all organic matter . - Reagent contain no hazardous metal. - Stable for room temperature. Which type of sewage we prefer COD test ? - Industrial sewage which do not respond BOD test .
  10. 10. Advantage of COD test - It take less time . - COD test oxidize a wide range of chemical compound . Disadvantage of COD test - It is inability to differentiate the biological oxidizable and biologically inert organic matter . - some organic compound aren't oxidise completely which contain carbon compound.
  11. 11. Prepared By: Masud alam Ansari