FACULTY OF CIVIL & ENVIRONMENTAL ENGINEERING

DEPT.OF WATER RESOURCES AND ENVIRONMENTAL ENGINEERING

ENVIROMENTAL ENGINEERING LABORATORY

SHORT REPORT

SUBJECT CODE BFC 32501

TEST CODE & TITLE CHEMICAL OXYGEN DEMAND (COD)

COURSE CODE 3 BFFTESTING DATE 29 FEBRUARY 2012GROUP 3

GROUP MEMBER NAMES

MOHD SAIFULIZHAM BIN JAMAL CF 100515

MOHD RAZIF BIN ROSLAN CF 100514

IZAIDAH BINTI ADNAN CF 100299

HANIM BTE ZAKARIA CF 100239

JEE SYE ENG CF 100340

LECTURER/ INSTRUCTOR/

REPORT RECEIVED DATE 6 MARCH 2012

MARKSPARTICIPATION/ DISCIPLINE /15%

DATA ANALYSIS /25%

RESULT /30%

DISCUSSION /30%

TOTAL /100%EXAMINER COMMENT RECEIVED STAMP

STUDENT CODE OF ETHIC(SCE)

DEPARTMENT OF WATER RESOURCES AND ENVIROMENTAL ENGINEERING

FACULTY OF CIVIL & ENVIRONMENTAL ENGINEERING

UTHM

I, hereby confess that I have prepared this report on my own effort. I also admit not to

receive or give any help during the preparation of this report and pledge that everything

mentioned in the report is true.

NAME MATRIC NUMB. SIGNATURE

Mohd Saifulizham bin Jamal CF 100515

Mohd Razif bin Roslan CF 100514

Izaidah binti Adnan CF 100299

Hanim bte Zakaria CF 100239

Jee Sye Eng CF 100340

1.0 OBJECTIVES

To measure the effectiveness of waste water sample (usually industrial waste water)

through the oxidation and reduction reaction.

2.0 LEARNING OUTCOMES

At the end of the study, student will be able:

a. To identify the principle of dichromate method to determine COD.

b. To evaluate the water parameter quality in domestic waste water sample and

water supply.

c. To choose the appropriate analytical methodologies water quality

measurement.

3.0 THEORY

COD or Chemical Oxygen Demand is the total measurement of all chemicals in

the water that can be oxidized. COD is used as a measurement of pollutants in

natural and waste waters to assess the strength of discharged waste such as

sewage and industrial effluent waters. It is normally measured in both municipal

and industrial wastewater treatment plants and gives an indication of the

efficiency of the treatment process. The dichromate reflux method is preferred

over procedures using other oxidants because of superior oxidizing ability,

applicability to a with wide variety of samples, and ease of manipulation. 

Oxidation of most organic compounds is 95-100% the theoretical value.

Most types of organic matter are oxidized by a boiling mixture of chromic and

sulfuric acids.  A sample is refluxed in strongly acid solutions with a known

excess of potassium dichromate (K2Cr2O7).  After dilution the remaining

unreduced  K2Cr2O7 is titrated with ferrous ammonium sulphate to determine the

amount of  K2Cr2O7 consumed and oxidizable  organic matter is calculated in

terms of oxygen equivalent. Keep ratios of reagent weights, volumes and

strengths constant when sample volumes other than 50 ml are used.  The standard

2 hours reflux time may be reduced if it has been shown that a shorter period

yields the same results

4.0 EQUIPMENT

a. COD Reflux System – consisting Erlenmeyer flask (250 mL or 500 mL) with

ground glass 24/40 neck and 300-mm jacket Liebig West, or equivalent condenser

with 24/40 ground-glass joint, and a hot plate having sufficient power to produce

at least 1.4 W/cm2 of heating surface.

b. Burette

c. Pipette

d. Glass beads

e. Magnetic stirrer bars

f. Chemical required : - Standard potassium dichromate (K2Cr2O7) 0.04167N

-Sulfuric acid (H2SO4)

-Ferrous ammonium sulfate (FAS)

-[Fe(NH4)2(SO4)2

-Ferroin indicator (ferrous ammonium sulfate)

-Dilution water

4.1 REAGENT

a. Standard potassium dichromate (K2C2O7) solution (0.04167 M) : (Prepare

by the technician; Dissolve 12.259 g K2Cr2O7, primary standard grade,

previously dried at 150°C for 2 hours in distilled water and dilute to 1000

mL). Notes: This reagent undergoes a six-electron reduction reaction; the

equivalent concentration is 6 X 0.04167M or 0.2500N.

b. Mercuric sulfate (Hg SO4)

c. Sulfuric acid reagent : (Prepare by the technician : Add Ag2SO4, reagent or

technical grade, crystals or powder, to concentration H2SO4 at the rate of

5.5 g Ag2SO4 /kg H2 SO4. Mix) phenanthroline monohydrate and 695 mg

FeSO4·7H2O in distilled water and dilute to 100 mL. This indicator solution

may be purchased already prepared).

b.Standard ferrous ammonium sulfate or FAS (Fe (NH4)2(SO4)2 solution

(0.25 M) titrant.

5.0 PROCEDURE

5.1 FAS Test

a. Measured 10 mL of standard potassium dichromate, 30 mL of sulhuric

acid and 20 mL of diluted water and add them together in refluxing flask.

b. Make sure added the solution in the fune chamber.

c. The solution must be cooled first with the flow water before continue the

experiment.

d. Added the solution with 3 drops of ferroin indicator.

e. Put magnetic stirrer into the refluxing flask and the solution was swirled

slowly while adding Ferrous ammonium into the solution until the

solution changed to light green color.

c.Added some 3 drops of the ferroin indicator again into solution and stir

again the solution with ferrous ammonium until the solution became

reddish brick.

d. Take the initial and final reading at the burette.

5.2 Reflux Test

a. Measured 20 mL of sample, 10mL standard potassium dichromate, 30

mL of sulfuric acid and add them together in refluxing flask.

b. Make sure added the solution in the fune chamber.

c. Heat the solution in 1 hours.

d. Cooled the solution in room temperature.

e. Rinsed the condenser with dilution water.

f. Added the dilution water into refluxing flask until at 150mL.

e. Added the solution with 2 to 3 drops of ferroin indicator.

f. Put magnetic stirer into the refluxing flask and the solution was

swirled slowly

while adding Ferrous ammonium into the solution until the solution

changed

to light green color.

g. Added some 3 drops of the ferroin indicator again into solution and stir

again the solution with ferrous ammonium until the solution became

reddish brick.

h. Take the initial and final reading at the burette.

6.0 DATA AND CALCULATION

FAS Result

Reading of Buret Cone Flask

(standard)

First Reading 0

Last Reading 10.5

Volume of FAS

standard (mL)10.5

Table 1: FAS standard titration data

Volume of FAS standard (mL) = 10.5 – 0

= 10.5 mL

Compute the molarity for the FAS standard using formula :

10 mL

= 0.23 < N < 0.28 …ok!!

Reflux Result

Sample (Cone Flask B) Blank (Cone Flask A)

DATA: DATA :

First Reading 20.0Last Reading 30.0Volume Reading 10.0

CALCULATION :

B = 9.8

CALCULATION :

A = 10.0

Table 2: Sample and Blank titration data

COD CALCULATION :

= 38.1 mg/l

First Reading 11.0Last Reading 20.8Volume Reading 9.8

7.0 DISCUSSION

7.1 What is the purpose of using blank sample in the experiment?

The main reason for using the blank sample is to control the volume of

organic material in the sample. COD was carried out to measure the oxygen

demand of organic compounds in a sample of water, and we have to ensure

there were no accidentally outside organic materials added to the sample to be

measured. A blank sample is created by adding the reagents to a volume of

distilled water. Both water and blank sample will be compared. The oxygen

demand for the blank sample is subtracted from the COD for the original

sample to ensure the true measurement of organic matter.

7.2 Name the oxidation and reduction agent used in COD test

Agent of oxidation and reduction is Potassium dichromate and Sulfuric acid

7.3 Give the chemical formula of the following:

a. Sulfuric acid : H2SO4

b. Ferrous Ammonium Sulfate : Fe(NH4)2(SO4)2

c. Pottasium dichromate : K2Cr2O7

d. Argentum sulfate : Ag2SO4

e. Mercuric Sulfate : Hg SO4

7.4 Calculate the molecular mass of the following:

a. Sulfuric acid

(1.00794 x 2) + 32.065 + (15.9994 x 4) = 98.07848 g/mol

b. Ferrous Ammonium Sulfate

55.845+[14.0067+(1.00794 x 4) x 2] + [32.065 + (15.9994 x 4) x 2] = 284.04

g/mol

c. Pottasium dichromate

(39.098 x 2) + (51.996 x 2) + (15.999 x 7) = 294.18 g/mol

d. Argentum sulfate

(39.948 x 2) + 32.065 + (15.999 x 4) = 175.96 g/mol

e. Mercuric Sulfate

200.59 + 32.065 + (15.999 x 4) = 296.65 g/mol

7.5 Explain the precaution that must be taken during COD test

a. Collect the samples in glass bottles, if possible. Use of plastic containers is

permissible if it is known that no organic contaminants are present in the

containers. 

b. Biologically active samples should be tested as soon as possible. Samples

containing settleable material should be well mixed, preferably homogenized,

to permit removal of representative aliquots.

c. Always do a risk assessment before start any experiment. Sulfuric acid is toxic

and corrosive so wear protective glove.

d. Make sure the Potassium dichromate (K2Cr2O7) is mixed and swirled well

with distilled water. 

e. Chloride, present in samples is oxidised. Mercuric sulphate is used as a

complexing agent.

f. Nitrite, ferrous iron, sulphide, exert COD. However their concentration in

water samples is low.

g. Amino nitrogen is released as ammonia.

h. Aromatic hydrocarbons and pyridines are not oxidised.

i. Samples for COD may be preserved by acidification to pH 2 or lower

8.0 CONCLUSION

Based on the result that we have from the COD test are succeed because

the FAS value is in range of 0.23 – 0.28 in FAS. FAS value that we get is 0.238.

From FAS, we can get the COD result. From calculation, were get 38.1 mg/l for

COD. The sample 38.1 mg/l is amount of oxygen (COD) consumed to completely

chemically oxidize the organic water constituents to inorganic end products. Now the

student know why the conclusion or result is must need in the each the experimental.

Chemical oxygen demand (COD) is a common, environmental procedure for

measure of the capacity of water to consume oxygen in the sample. COD is used as a

measurement of pollutants in natural and waste waters to assess the strength of

discharged waste such as sewage and industrial effluent waters. The COD test also is

used to measure the strength of wastes that are too toxic for the BOD test. The COD

test will give a good estimate of the first stage oxygen demand for most wastewaters.

An advantage of the COD test over the biochemical oxygen demand (BOD) test is 2 to

3 hours versus 5 days. The COD test should be considered an independent

measurement and not a quick substitute for the BOD test. The COD is usually higher

than the BOD, but the amount will vary from waste to waste.

As a conclusion, from the value of COD is 38.1 mg/L that we get from the

experiment was successful because the value of normality of FAS (n) is 0.238 was in

the range that required. But we cannot compare to the BOD caused as we know the

value of BOD is 1/3 COD.

9.0 REFERENCES

a. Hammer, MarkJ. (2001)”Water and Waste water Technology Fourth Edition”

New Terzey: Prentice Hall

b. Master, Gelbert M (1998) “ Introduction to Environmental Engineering and

Science” New Terzey : Prentice Hall

c. Davis Cornwell (2008) “Introduction to Environmental Engineering” Fourth

Edition, New York:Mc Graw Hill