The document discusses the biochemical oxygen demand (BOD) method for determining sewage quality. It defines BOD as the amount of dissolved oxygen needed by organisms to break down organic material in water. The most common BOD test is the 5-day BOD (BOD5) test, which measures the oxygen demand over a 5-day incubation period at 20°C. Elevated BOD levels can be caused by human/animal waste, fertilizer runoff, and higher water temperatures that increase plant growth. The document outlines the detailed procedures for conducting the BOD5 test and analyzing the results. It notes advantages of the test being simple and widely used but disadvantages include its long incubation period and susceptibility to inhibition.

1. Seminar on
SEWAGE DETERMINATION BY BIOCHEMICAL
OXYGEN DEMAND METHOD
PRESENTING BY –
RAHUL KUMAR SAHU
M.Sc. (RT) 2 nd SEMESTER
DEPARTMENT OF RURAL TECHNOLOGY AND SOCIAL
DEVELOPMENT ,
SESSION – 2018-19

2. CONTENTS –
 Definition
 BOD
 Why measure BOD
 Factors effected BOD levels
 The method of measuring BOD
 The procedures for the 5 – day BOD , BOD5 test
 Advantage and disadvantage of BOD
 Conclusion
 References

3. DEFINITION –
Biochemical Oxygen Demand (BOD) also called Biological Oxygen
Demand is the amount of dissolved oxygen needed (i.e. demanded)
by aerobic biological organisms to break down organic material
present in a given water sample at certain temperature over a
specific time period . The BOD value is most commonly expressed in
milligrams of oxygen consumed per litre of sample .

5. Why Measure BOD –
Biological oxygen demand is an important water quality parameter
because it greatly influences the concentration of DO ( Dissolve
oxygen ) that will be in the water.

7. Factors affect BOD levels –
 Human and animal waste in sewage is a significant contributor to
elevated BOD levels.
 Runoff containing fertilizer from farms and other sources
contributes to accelerated eutrophication, in which water bodies
become choked with excessive plant growth, which contributes to
the carbonaceous (organic) content of water bodies as these plants
die and decompose.
 Elevated temperature decreases the level of dissolve
oxygen of water harming aquatic organisms like fish ,
amphibians and others .

8.  Higher water temperature increases plant growth rates .
 This results in a shorter lifespan and species overpopulation
causing an “algae bloom” which reduces oxygen levels .
 Eutrophication occurs due to
over supply of nutrients , which
causes explosive growth of
plants and algae .

11. The method of measuring (BOD) –
 The most common method of measuring BOD is the “5 day” BOD
method (BOD5), which is a method approved by , Environmental
protection agency (EPA) United states for use during monitoring in
the BOD5 test , which uses naturally occurring microorganisms to
oxidize the carbonaceous organic matter , the change in dissolve
oxygen concentration is measured before and after a 5 – day period
in water samples that are incubated at a specified temperature
(20˚C – 1˚C ) in darkness .
 The BOD5 method measures most of the carbonaceous stage of
the BOD (typically about 60% to 70%) showing biological oxygen
demand . This method has been widely adopted as a standard ,

12. The procedures for the 5 – day Biochemical oxygen demand
(BOD5) test –
1. The water sample must be reperesentative of the larger water body .
2. The test must be initiated within 2 hours of collecting the water sample
, or the sample must be refrigerated (4˚C ) for up to 48 hours before
initiating the BOD5 test .
3. Special BOD bottles that minimize the accidental introduction of
oxygen or nutrients must be used .
4. Glassware and pipets must be scrupulousely change with a non –
phosphate detergent and with multiple rinses with distilled or
deionized water to avoid introducing nutrients or toxins .
5. An aquarium pump , tubing and air diffusion stone are needed , and

13. 6.The pH must be maintained between 6.5 and 7.5 using NaoH and
H2SO4 if necessary .
7.A nutrient dilution solution containing Cacl2 , Fecl3 , Mgso4 and
phosphate buffer must be prepared using very high quality water
that contains no nutrients or toxins these solution supports the
growth of the bacteria used in the assay it should be discarded in
the event that bacterial growth occurs in it .
8.The dissolve oxygen sensor must be calibrated at the current
atmospheric pressure and the temperature of the water sample
before each days measurement .
9.The test sample must be incubated in the dark at 20˚C ≠ 1˚C .
10.Any residual chlorine , if present must be removed before the

14. 11. A sample that has been treated by disinfectants may need to be
“seeded” with bacteria .
12. a negative (blank) and positive (glucose glutamic acid standard
solution) control must be run with the test and results of these
must meet standards .

15. Advantage and disadvantage of BOD test –
Advantage –
Simple , popular
Used in the majority of design equations .
Produces information on both carbonaceous and nitrogenous
oxygen demand .
Disadvantage –
Long period of incubation
Reproducibility poor (15%)
Susceptible to inhibition by many industrial wastes .

16. Conclusion –
The more “food” present in the waste , the more dissolved oxygen
will be required . The BOD test measures the strength of the waste
water by measuring the amount of oxygen used by the bacteria as
they stabilize the organic matter under controlled conditions of time
and temperatures .

17. Reference –
 National field manual for the collection of water quality
data . Vol. 7.2 , techniques of water resources
investigations reports :-
United states geological survey : 1999
 National science foundation . Water quality index , 2004

18. THANKYOU