The document describes an experiment to measure biochemical oxygen demand (BOD) of various water samples. BOD is a measure of the amount of oxygen consumed by microorganisms as they break down organic matter in water. The experiment involves taking water samples from a river, lake, and rain water, incubating them for 5 days, and measuring the dissolved oxygen levels initially and after 5 days. The BOD values were calculated and reported. The results showed that river water had the highest BOD at 2.4 mg/L, indicating more organic matter to be broken down by microbes. The conclusion discusses how BOD is used to understand how organic pollutants affect dissolved oxygen levels in water bodies.

1. MONEESHA SRI GOBINATHAN
EXPERIMENT OXYGEN DEMAND, BIOCHEMICAL
1
October18, 2021
1. INTRODUCTION
Microorganisms such as bacteria are responsible for decomposing organic waste.
When organic matter such as dead plants, leaves, grass clippings, manure, sewage,
or even food waste is present in a water supply, the bacteria will begin the process of
breaking down this waste. When this happens, much of the available dissolved oxygen
is consumed by aerobic bacteria, robbing other aquatic organisms of the oxygen they
need to live. Biochemical oxygen demand or BOD is a procedure to determine the
amount of oxygen consumed by the microorganisms in the waste water chemically. It
is commonly used as the indicator to show the cleanliness of the waste water.
2. OBJECTIVE
To measure the amount of dissolved oxygen in the waste water for a specified period
of time and temperature.
3. THEORY
BOD is defined as the amount of oxygen required by living organisms in the
stabilization of the organic matter of water. If the oxidation of an organic compound is
carried out by microorganisms using the organic matter as a food source, the oxygen
is consumed. The greater the amount of organic matter present, the greater the
amount of oxygen utilized. The BOD test is indirect measurement of organic matter.
Since the test is performed over a five day period, it is often refferred as five day BOD
(BOD5).
It is generally assumed that the rate at which oxygen is consumed directly proportional
to the concentration of degradable organic matter remaining at any time. Different
result would be obtained at different temperatures because biochemical reaction rates
are temperature-dependent. The kinetics of the BOD reaction are, for particle
purposes, formulated in accordance with first-order reaction kinetics and may be
expressed as
dL / dt = - kLt
where, Lt is the amount of the first stage BOD remaining in the water at time t and k is
the reaction rate constant. This equation can be integrated as
ln Lt / L = - kt or
The amount of BOD remaining at time t equals
Lt = L e-kt
and y the amount of BOD that has been exerted at any time t, equals
BODt = L( 1 – e-kt )

2. MONEESHA SRI GOBINATHAN
EXPERIMENT OXYGEN DEMAND, BIOCHEMICAL
2
October18, 2021
For five day BOD (BOD5), the sample is kept in incubator which remains around 20oc.
Most of the biological process sprrd up as the temperature increase and slow down
as the temperature drop. The temperature of 20oc is standard temperature in lab and
it is suitable for the bacteria active in breaking down the waste.
4. APPARATUS
BOD BOTTLE
DILUTION WATER
NUTRIENT BUFFER
PILLOW

3. MONEESHA SRI GOBINATHAN
EXPERIMENT OXYGEN DEMAND, BIOCHEMICAL
3
October18, 2021
BOD TESTING
PIPET
INCUBATOR

4. MONEESHA SRI GOBINATHAN
EXPERIMENT OXYGEN DEMAND, BIOCHEMICAL
4
October18, 2021
5. PROCEDURE
i. Prepare the dilution water using a BOD Buffer Pillow Dilution water
preparation.
ii. Select the sample volumes. See Sample size selection Note: If the
minimum sample volume is 3 mL or more, determine the dissolved
oxygen in the undiluted sample; this determination can be omitted when
analysing sewage and settled effluents known to have a dissolved oxygen
content near 0 mg/L. When analyzing disinfected samples or industrial
effluents, refer to Interferences.
iii. Stir the sample gently with the pipet. Use the pipet to add the minimum
sample volume to the first BOD bottle. Add the remaining four sample
volumes to four more BOD bottles. Mark the bottles and record the
contents of each bottle.
iv. Fill an additional BOD bottle with dilution water only. This will be the
dilution water blank. Report results as CBOD.
v. If the test is for CBOD, add two portions of Nitrification Inhibitor
(approximately 0.16 g) to each bottle. The oxidation of nitrogen compounds
will be prevented.
vi. Fill each bottle to just below the lip with dilution water. Allow the dilution
water to flow down the sides of the bottle to prevent air bubbles from
becoming trapped in the bottle.
vii. Stopper the bottles carefully to prevent air bubbles from becoming trapped.
Tightly twist the stopper into place. Press down on the stopper and invert
the bottles several times to mix.
viii. Measure the initial dissolved oxygen concentration in each bottle. Use a
probe and meter or titration. If a titration is used, two sets of BOD
bottles must be prepared. Be sure to measure the DO of the dilution
water blank.
ix. Stopper the bottles carefully to prevent air bubbles from becoming trapped.
Add dilution water to the lip of each BOD bottle to make a water seal.
x. Place a plastic cap over the lip of each bottle. Put the bottles in an
incubator at 20 (±1) °C. Incubate for five days.
xi. After five days, measure the remaining dissolved oxygen concentration in
each bottle. At least 1.0 mg/L DO should be left in each BOD bottle.
xii. Calculate the BOD value (see Calculation Methods—Standard.
6. RESULT

5. MONEESHA SRI GOBINATHAN
EXPERIMENT OXYGEN DEMAND, BIOCHEMICAL
5
October18, 2021
SAMPLE D1 (mg/L) D2 (MG/L) BOD5
RIVER WATER 6.81 5.61 2.4
LAKE WATER 6.72 5.68 2.08
RAIN WATER 5.75 4.60 2.30
DILUTION
WATER
7.97 7.28 1.38
BOD = D1-D2
0.5
7. CALCULATION

6. MONEESHA SRI GOBINATHAN
EXPERIMENT OXYGEN DEMAND, BIOCHEMICAL
6
October18, 2021
8. DISCUSSION
About the trend , it is clear above that the bod consumed is not linearly related to the
time , since the organic matter consumption is a first order reaction and hence it would
produce an exponential time dependent function . There is two types of tests seeded

7. MONEESHA SRI GOBINATHAN
EXPERIMENT OXYGEN DEMAND, BIOCHEMICAL
7
October18, 2021
test and unseeded test In unseeded test , bacteria microorganism is already there , all
u need to add is the dilution water + nutrient for them to work . So that when u find C
of O2 consumed all u have is to divide by the dilution factor to take in to consideration
the effect of the dilution water that the concentration of organic matter has been diluted
too .
9. CONCLUSION
Biochemical oxygen demand (BOD) represents the amount of oxygen consumed by
bacteria and other microorganisms while they decompose organic matter under
aerobic (oxygen is present) conditions at a specified temperature.
When you look at water in a lake the one thing you don't see is oxygen. In a way, we
think that water is the opposite of air, but the common lake or stream does contain
small amounts of oxygen, in the form of dissolved oxygen. Although the amount of
dissolved oxygen is small, up to about ten molecules of oxygen per million of water, it
is a crucial component of natural water bodies; the presence of a sufficient
concentration of dissolved oxygen is critical to maintaining the aquatic life and
aesthetic quality of streams and lakes.
The presence of a sufficient concentration of dissolved oxygen is critical to maintaining
the aquatic life and aesthetic quality of streams and lakes. Determining how organic
matter affects the concentration of dissolved oxygen (DO) in a stream or lake is integral
to water- quality management. The decay of organic matter in water is measured as
biochemical or chemical oxygen demand. Oxygen demand is a measure of the
amount of oxidizable substances in a water sample that can lower DO concentrations.
Certain environmental stresses (hot summer temperatures) and other human-induced
factors (introduction of excess fertilizers to a water body) can lessen the amount of
dissolved oxygen in a water body, resulting in stresses on the local aquatic life. One
water analysis that is utilized in order to better understand the effect of bacteria and
other microorganisms on the amount of oxygen they consume as they decompose
organic matter under aerobic (oxygen is present) is the measure of biochemical
oxygen demand (BOD).
Determining how organic matter affects the concentration of dissolved oxygen in a
stream or lake is integral to water-quality management. BOD is a measure of the
amount of oxygen required to remove waste organic matter from water in the process
of decomposition by aerobic bacteria (those bacteria that live only in an environment
containing oxygen). The waste organic matter is stabilized or made unobjectionable
through its decomposition by living bacterial organisms which need oxygen to do their
work. BOD is used, often in wastewater-treatment plants, as an index of the degree of
organic pollution in water.
10. Reference
a. https://www.slideshare.net/anasmaghayreh/bod-54957912
b. https://www.google.com/search?q=biochemical+oxygen+demand++discussion&rlz=1C1UEAD
_enMY971MY971&sxsrf=AOaemvL4Eu3T98150NHMGtSUSNElKEZzyA:1634894333425&so

8. MONEESHA SRI GOBINATHAN
EXPERIMENT OXYGEN DEMAND, BIOCHEMICAL
8
October18, 2021
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EQAw&biw=1280&bih=520&dpr=1.5#imgrc=V_fd7UBTVnqdMM
c. https://www.scribd.com/doc/307224471/BOD-Lab-Report
d. https://www.scribd.com/document/215322468/BOD-Discussion
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C1UEAD_enMY971MY971&oq=&aqs=chrome.2.35i39i362l8...8.589658077j0j15&sourceid=c
hrome&ie=UTF-8