Chemical oxygen demand (COD) is a measure of the oxygen-consuming capacity of inorganic and organic matter in water. COD determines the amount of oxygen required to oxidize organic compounds and inorganic matter in water. There are two main methods to measure COD - the open reflux method and closed reflux method. The open reflux method involves refluxing the sample and dichromate solution for 2 hours, then titrating the remaining dichromate with ferrous ammonium sulfate to determine COD concentration in mg/L. A high COD means more oxidizable organic material is present in water, which can reduce dissolved oxygen and harm aquatic life. COD is useful for assessing waste strength and effects on receiving environments

2. Chemical Oxygen Demand (COD)
Presented To: Ms. Noor us Sabah
Presented by:
Muhammad Usman E256
Hafiz Ali Usman M044
Asif Ayub E231
Abubakar M101
Abdul Majid M069

3. Chemical oxygen demand (COD)
• In environmental chemistry, the chemical oxygen demand (COD) is
an indicative measure of the amount of oxygen that can be consumed
by reactions in a measured solution.
• Chemical oxygen demand (COD) is a measure of the capacity
of water to consume oxygen during the decomposition of
organic matter and the oxidation of inorganic chemicals such as
Ammonia and nitrite.
• COD is expressed in mg/L, which indicates the mass of oxygen
consumed per liter of solution.

4. Chemical oxygen demand (COD) cont.
• Chemical Oxygen Demand or COD is a measurement of the oxygen
required to oxidize soluble and particulate organic matter in water.
• The temperature of stream water influences the amount of dissolved
oxygen present; less oxygen dissolves in warm water than cold water.
For this reason, there is cause for concern for streams with warm
water. Trout need DO levels in excess of 8 mg/liter, striped bass prefer
DO levels above 5 mg/l, and most warm water fish need DO in excess
of 2 mg/l.

5. WHY IS IT IMPORTANT?
• Chemical Oxygen Demand is an important water quality parameter
because, similar to BOD, it provides an index to assess the effect
discharged wastewater will have on the receiving environment. Higher
COD levels mean a greater amount of oxidizable organic material in
the sample, which will reduce dissolved oxygen (DO) levels. A
reduction in DO can lead to anaerobic conditions, which is deleterious
to higher aquatic life forms. The COD test is often used as an alternate
to BOD due to shorter length of testing time.

7. B.O.D Vs C.O.D
• B.O.D
BOD is only a measurement of
consumed oxygen by aquatic
microorganisms to decompose or
oxidize organic matter.
C.O.D
COD refers the requirement of
dissolved oxygen for the oxidation
of organic and inorganic
constituents both
Although, some of the organic compounds, which can be broken
down by microorganisms, are countable for the biological
oxygen demand, they may not be encountered in measuring
chemical oxygen demand

8. Environmental significance
• COD values are particularly important in the surveys designed to
determine and control the losses to sewer systems.
➢The ratio of BOD to COD is useful to assess the amenability of waste
for biological treatment . Ratio of BOD to COD greater than or equal to
0.8 indicates that wastewater highly polluted and amenable to the
biological treatment.
➢It is useful to assess strength of wastes ,which contain toxins and
biologically resistant organic substances.

9. Procedure for COD measurement
• It is important to understand that COD and BOD do not necessarily
measure the same types of oxygen consumption. For example, COD
does not measure the oxygen-consuming potential associated with
certain dissolved organic compounds such as acetate. However, acetate
can be metabolized by microorganisms and would therefore be
detected in an assay of BOD. In contrast, the oxygen-consuming
potential of cellulose is not measured during a short-term BOD assay,
but it is measured during a COD test.

10. Procedure for COD measurement
• Two types method for COD measurement
1. Open Reflux Method
2. Closed Reflux Method
Mostly use the Open Reflux Method because close reflux method is
produce the minimum hazaradous wastes but cost advantage.

11. Open Reflux Method
• The sample and a blank are refluxed in strongly acidic solution in the
presence of standard potassium dichromate solution for 2 hours using
a reflux apparatus comprising of an Erlenmeyer flask, a vertical
condenser and heating mantle.
• The remaining unreduced dichromate of the digested sample and blank
are measured by titrating against standard ferrous ammonium sulfate
(FAS) solution using ferroin indicator.
• The COD test only requires 2-3 hours, while the Biochemical (or
Biological) Oxygen Demand (BOD) test requires 5 days.

12. Erlenmeyer flask Heating mantle

13. Open Reflux Method (cont.)
• Potassium dichromate is a strong oxidizing agent under acidic
conditions. Acidity is usually achieved by the addition of sulfuric acid.
• 0.25 N solution of potassium dichromate is used for COD
determination.
• For all organic matter to be completely oxidized, an excess amount of
potassium dichromate (or any oxidizing agent) must be present. Once
oxidation is complete, the amount of excess potassium dichromate
must be measured to ensure that the amount of Cr3+ can be
determined with accuracy.

14. Open Reflux Method (cont.)
• To do so, the excess potassium dichromate is titrated with ferrous
ammonium sulfate (FAS) until all of the excess oxidizing agent has
been reduced to Cr3+. Typically, the oxidation-reduction
indicator ferroin is added during this titration step as well. Once all
the excess dichromate has been reduced, the ferroin indicator
changes from blue-green to a reddish brown.

15. Open Reflux Method (cont.)
• Calculations
8000(b-s)n
sample vol.
• where b is the volume of FAS used in the blank sample, s is the
volume of FAS in the original sample, and n is the normality of FAS. If
milliliters are used consistently for volume measurements, the result
of the COD calculation is given in mg/L.
COD=

16. Precision and Bias
• A set of synthetic samples containing potassium hydrogen phthalate
and NaCl was tested by 74 laboratories. At a COD of 200 mg O2/L in
the absence of chloride, the standard deviation was 13 mg/L
(coefficient of variation, 6.5%). At COD of 160 mg O2/L and 100 mg
Cl/L, the standard deviation was 14 mg/L (coefficient of variation,
10.8%). (PITWELL, L.R. 1983. Standard COD. Chem. Brit. 19:907.)
• Disadvantages:
1. Do not differentiate between the biologically oxidizible and inert substances
2. Do not indicate the rate of reaction
Advantages: Short time required for evaluation

17. Objectives of the study:
• To combat or reduce disease burden among human beings and animals the
above topic is taken with the following objectives:
1. To collect information on the collection, treatment, handling, hauling, and
disposal of medical wastes.
2. To determine the level of knowledge and awareness of individuals
involved in the medical waste in Lucknow’s hospitals.
3. To determine the physico-Chemical properties of hospital waste water and
soil collected nearby the selected hospitals of Lucknow city.
4. To examine the water quality of hospital waste water.
5. To collect the data of infectious and non-infectious and recyclable waste
in the selected hospitals of Lucknow.
6. To assess the heavy metals contents in waste water in the studied
hospitals.