An Overview of Phenomenon of BOD and COD

International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056
Volume: 04 Issue: 08 | Aug -2017 www.irjet.net p-ISSN: 2395-0072
© 2017, IRJET | Impact Factor value: 5.181 | ISO 9001:2008 Certified Journal | Page 264
An Overview of Phenomenon of BOD and COD
Prof.Akshaya.G.Ghalimath,
1Assistant Professor, Indira College of Engineering and Management
3Example: Assistant Professor, Dept. Civil Engineering, Indira College of Engineering and Management,
Maharashtra, India
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Abstract - Real-time monitoring of water quality for sewer
system is required for efficient sewer network design
because it provides information on the precise loading of
pollutant to Wastewater treatment facilities and the impact
of loading on receiving water. In this study, biochemical
oxygen demand (BOD) and chemical oxygen demand (COD)
phenomenon discussed. The temporal variationsinBODand
COD for urban areas whereas they were relatively irregular
for non-urban areas. Irrespective of the sewer pipes and the
types of the areas, it will be changes.
Key Words: BOD, COD, Chemicals required, THOD,
Limitation of BOD and COD etc.
1. INTRODUCTION
Biochemical Oxygen Demand
The Quantity of Oxygen Used in theBiochemical Oxidation of
Organic Material.
Under:
Specified Time 5 Days
Specified Temperature 20
Specified Conditions In the Dark
In the Presence of Bacteria
(to prevent algae growth and photosynthesis of O2)
1.1 Impact of BOD on dissolved oxygen in a river
1.2 Stages of BOD
First stage BOD- Carbonaceous
Second stage BOD-Nitrogenous
2. THEORITICAL OXYGEN DEMAND (THOD)
Degradable organic matter is broken down by microbes,
usually with the help of oxygen, although in the absence of
oxygen also anaerobic reactions (fermentation and
methanogens) are possible. C2H5OH + 3 O2
2 CO2 + 3 H2O ThOD of C2H5OH = = 2.08 mg O2/mg ethanol
THEORITICAL OXYGEN DEMAND (THOD)
THOD is the total amount of oxygen required to completely
oxidize a known compound to CO2 and H2O. It is a
theoretical calculationthatdependsonsimplestoichiometric
principles. It can only be calculated on compounds ofknown
composition.
2.1 Seeding
Samples of domestic sewage and industrial effluents mixed
with sanitary sewage, in the pH range of 6 to 8.5 themselves,
contain enough living microorganisms and do not require
seeding.
• Samples of industrial organic wastes, such as sugar factory
wastes, paper & pulp mill wastes, textile wastes, distillery
wastes etc. require seeding particularly when their pH is
outside the range of 6 to 8.5.
• Samples, that are acidified and stored below 100 C for
preservation for some days before BOD determination,
require pH correction and seeding at the time of test.

• The seed may be bacteria from organically rich soil or the
supernatant of aerated domestic sewage or an extract from
the aerator mixed liquor of a successfully working ASP.
 Carbonaceous matter oxidation -5 days 20⁰C
 Nitrogenous matter oxidation-6-7 days
 BOD 5 days oxidation of organic matter is about 68-
70%
 20 days oxidation of organic matter is about 95-
99%.
2.2 Kinetics of BOD-
2.3 BOD Rate Constant (KD)-
KD determines the rate of BOD reaction. It varies with
temperature. Therefore, KD for some other temperature can
be worked out
• KD (T0) = KD (200C) (1.047) T-20⁰C
• At 200C, KD value for municipal wastewater is0.1/day.The
range of KD value is 0.05-0.2/day.
2.4 Significance of BOD-
Determining degree of H2O pollution.
•Important measurement in operation of sewage treatment
plant.
•Comparing BOD of incoming sewage & effluent efficiency,
effectiveness of treatment is judged.
• For example, in a typical residential city raw sewage has a
BOD value of around 300 mg/L. If the effluent from the
sewage treatment plant has a BOD. of about 30 mg/L, the
plant has removed 90 percent of the BOD.
2.5 Limitation of BOD-
Dilution is required.
• Measurement fails if dilution is too much or too less
• Pretreatment if toxic wastes.
• Long period of time.
• Seeding for industrial water.
3. COD
3.1 Definition-
Measure of the oxygen equivalent of organic matter in a
sample that is susceptible to oxidation by a strong chemical
oxidant. Rather than biologically decompose / oxidize
organic waste, here chemically decompose/oxidize organic
waste is done.
3.2 Principle behind COD-
A known volume of a potent oxidizing agent is used to
oxidize all oxidizable matters in the waste sample as
completely as possible. Oxidation is carried outforextended
period at 150 C.
•The residual oxidizing agent is estimated using a suitable
reducing agent. The amount ofoxidizingagentconsumed isa
measure of the overall pollution load of the waste.
3.3 Apparatus and Chemical Required-
Reflux apparatus comprising of 500 ml capacity RB flask
with ground glass joint and a water condenser.
•Chemicals
1. Standard 0.25 N K2Cr2O7 (1 ml ≡ 2mg of oxygen)
2.H2SO4-AgSO4 reagent
3. Standard 0.1 N Fe(NH4)2(SO4)2.6H2O
4. Ferron indicator-color of oxidized form is pale blue and of
reduced form is red
5. HgSO4 AR grade
3.3 Procedure of COD-
In RB flask-water sample + HgSO4 + distilled
Water + K2Cr2O7 + H2SO4-AgSO4 reagent. Heat it under
reflux for at least 2 hours. Cool the solution, dilute it and
titrate the unreacted K2Cr2O7 with FAS solution using
Ferroin as Indicator and get b ml

•Color at end-point changes from bluegreen(oxidizedform)
to wine red (reddish brown complex) (reduced form)
•Perform blank experiment with Distilled water instead of
the water sample and get a ml.
3.4 Accuracy of Test-
It is important that no outside organic material be
accidentally added to the sample to be measured. To control
for this, blank sample is used created by adding all reagents
(e.g. acid and oxidizing agent) to a volume of distilled water.
COD is measured for both and the two are comparedi.e.COD
of blank -COD of sample.
3.5Advantages-
 Correlates with BOD well
 Toxic chemicals do not interfere
 Short time for analysis
3.6 Limitation-
 Chemical Oxidant is not specific to oxygen-
consuming chemicals that are organic or inorganic,
both of these sources of oxygen demand are
measured in a COD assay.
 It does not distinguish between Biodegradable and
Non-Biodegradable organic matter.
 The test does not measure the oxygen demand
caused. by the oxidation of ammonia into nitrate.
4. Conclusion:
The water qualities of all surface water bodies that may be
river, reservoir, lake, stream, delta, and creek are very
important. Various researchers explained their views about
water quality parameters. The physical chemical and
Biological factors are investigated in this study to assess the
water quality and it is clear that all parameters are equally
important and broad range of parameters is to be studied
with more details for water quality modeling. Also, those
parameters were selected due to their simple, fast and
continuous measurement at water quality monitoring
stations. So it can be conclude that Temperature, pH, TDS,
EC, DO, BOD, COD are the broad range of water quality
parameters for drinking, irrigation, aquatic life for surface
water.
References:
1) American Public Health Association, American
Water Works Association, and Water
Environment Federation, Standard
2) Bougeois, W.; Burgess, J.E.; Stuetz, R.M. Online
monitoring of wastewater quality: A review. J.
Chem. Technol. Biot. 2001, 76, 337–348.
Methods for the Examination of Water and
Wastewater, vol. 21, American Public Health
Association, 2005
3) Willems, P. Quantification and relative
comparison of different types of uncertaintiesin
sewer water quality modeling. WaterRes.2008,
42, 3539–3551.

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