COD TEST (GROUP 3) – SECTION 4
BFC 32501
1.0 OBJECTIVES To determine the organic oxidize able matters content of water samples.
2.0 LEARNING OUTCOMES At the end of the study, the students will be able: a. To understand the oxidation of oxidize able matter with a known amount of potassium
chromate, the titration of excess chromate, and the calculation of oxygen used. b. To identify the organic oxidize able matter pollutant content in water samples.
c. To evaluate the water quality status at the location of water or wastewater sampling point. d. To choose the appropriate analytical methodology for measuring COD parameter.
3.0 THEORY The chemical oxygen demand (COD) is the amount of oxygen consumed to completely chemically oxidize the organic water constituents to inorganic end products. COD is an important, rapidly measured variable for the approximate determination of the organic matter content of water samples. Some water samples may contain substances that are difficult to oxidize. In these cases, because of incomplete oxidation under the given test methods, COD values may be a poor measure of the theoretical oxygen demand. It should also be noted that the significance of the COD value depends on the composition of the water studied. 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 wide variety of samples, and ease of manipulation. Oxidation of most organic compounds is 95100% the theoretical value.
COD TEST (GROUP 3) – SECTION 4
BFC 32501
4.0 EQUIPMENT
COD Reflux System – consisting Erlenmeyer flask (250 mL or 500 mL) with groundglass 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. 1.0 Burette 2.0 Pipette 3.0 Glass beads 4.0 Magnetic stirrer bars
5.0 PROCEDURE: 1. Sample is carried out by including materials into Erlenmeyer flask according
following order:
a) Prepare beaker 1 to 90mL waste water sample and beaker water 2 to 90 mL tap
water. b) include inside beaker 1 and 2: i.
0.0417M K2Cr2O7 - 10mL
ii.
concentrated sulphuric acid (which contains Ag2So4)* - 30mL
c) make sure sulphuric acid poured into flask reflux gradually as stir to avoid water vapour loss
COD TEST (GROUP 3) – SECTION 4
BFC 32501
2
Boil flask reflux (vaporization and perspiration) long 1 hours. Boiling could prevent organic substances boiling over of lost. While waiting 1 hours, another experiment on how to find the normality was being carried out
3
After 1 hours flask left up to cold. Condenser is washed with
flute and refrigeration water continued. Condenser take off.
4 Distilled water blend until volume achieve 140 mL. 2 to 3 solution drop indicator ferrion (1-10 fenantrolin). magnet stem included and is stirred use magnetic stirrer
COD TEST (GROUP 3) – SECTION 4
BFC 32501
5. Ammonia ferric sulphate (0.25M) has been standardized titrated to fixed color to the
first emerges. Alert because point color final can be change quickly. First and final reading burette is being recorded.
6. Ability provision titration: ammonium solution iron (II) sulphate prepared as follows: a) 90 mL distilled water and 10mL K2Cr2O7 standard (0.0147 M) included inside
250mL cone's flask. And shaked it slowly b) 30mL sulphuric acid H2SO4 added by careful and gradually concentrated acid
and coolness c) 2 to 3 indicator drop ferroin and titrated with ferrous ammonium sulphate and stir in slow. Titration discontinued after colour changed from blue greenness to red-brown.
COD TEST (GROUP 3) – SECTION 4
BFC 32501
blue greenness to red-brown.
6.0 DATA AND CALCULATION NORMALITY 1st
FIRST READING 9 ml
10 x 0.25 19 − 9
= 0.25 * ( 0.23 – 0.28) OK !!!
Waste water
Tap water
LAST READING 19 ml
COD TEST (GROUP 3) – SECTION 4
BFC 32501
DATA:
DATA :
First Reading Last Reading Volume Reading
15.8 23 0.18
CALCULATION :
10 x 0.25 23 − 15.8
= 0.18
COD CALCULATION :
= 0.85 mg/l nok tok xtauk
First Reading Last Reading Volume Reading
CALCULATION :
10 x0.25 15.8 − 5
= 0.27
5 15.8 0.27
COD TEST (GROUP 3) – SECTION 4
BFC 32501
7.0 DATA AND ANALYSIS
8.0 DISCUSSION 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.
COD TEST (GROUP 3) – SECTION 4
2.
BFC 32501
What is the objective of COD test and what is the different between COD and BOD test? -
The chemical oxygen demand (COD) is the amount of oxygen consumed to
completely chemically oxidize the organic water constituents to inorganic end products. It was carrying out to determine the organic oxidize able matters content of water samples. While, Biochemical Oxygen Demand is a common, environmental procedure for determining the extent to which oxygen within a sample can support microbial life. -
While BOD describes the biological oxidation capacity of a wastewater, it is not
a measure of the total potential oxidation of the organic compounds present in the wastewater. A number of chemical tests are used to measure this parameter, either in terms of the oxygen required for virtually complete oxidation, or in terms of the element carbon. Probably the most common test for estimating industrial wastewater strength is the Chemical Oxygen Demand (COD) Test. This test essentially measures the chemical oxidation of the wastewater by a strong oxidizing agent in an acid solution. The value for the COD test is always greater than the BOD test and is not always a good indication of BOD values for the same waste. -
Because
the
COD
test
oxidizes
both
biologically
degradable
and
unbiodegradable organic materials, the energy available for biological action is usually overestimated. However, this does not reduce the usefulness of the test. If it is assumed that the fraction of organic material that is not oxidized in the COD test remains constant, then any change in COD between two points in the process provides an assessment (in terms of oxygen) of corresponding energy change. The change in COD then can be used to establish the kinetics of energy conversion in the process, i.e., the energy removal can be directly linked to the COD change. By contrast, BOD5 values require a correction factor to correspond the energy changes, because the test values do not reflect the total oxygen demand.
COD TEST (GROUP 3) – SECTION 4
3.
BFC 32501
Why the COD’s value needs to be monitor for the polluted surface water such as in lakes and rivers as well as for waste water? -
In environmental, the chemical oxygen demand (COD) test is commonly used
to indirectly measure the amount of organic compounds in water. Most applications of COD determine the amount of organic pollutants found in surface water such as lakes and rivers, making COD a useful measure of water quality. The amount of organic mater in the lake or river will show the index of the water quality and we also can categorize whether the lake or river extremely polluted or not.
9.0 CONCLUSION The result we have during the test lab of COD after the analysis and calculation actually are succeed and is not more different from the accurate reading when to do until third test, at first test lab we got the 0.297 for NAS, we have the result is bad and not accurate, the result must in range 0.23 – 0.28 in NAS, and from NAS, the calculation of COD can make to get the result for the sample. The was on experimental of my group, result had we got are not accurate because the range has the provide is place at out, after the experiment try again, we obtain the result are present at in the range, so from mistake data we obtain, we can say the experiment has we do the time when the sample in distilled water plus with reagent, then agen chemical sulphuric together, let the sample are cooled in warm, after that 2 to 3 indicator drop ferroin and titrated with ferrous ammonium sulphate and stir in slow, titration discontinued after colour changed from blue greenness to red-brown, that should be, but my group has identified and post mortem, the answer we are slow and to late acting for discontinued of the titration, so that the reading of the ammonium sulphate are had we take are less even one driblets. The one driblets are able to change the data for calculation of COD.
The lastly after got the result of NAS are in range, so we proceed to get the COD with another calculation, the result of NAS are to will use for calculation of COD, from calculation,
COD TEST (GROUP 3) – SECTION 4
BFC 32501
were obtain 0.85 mg/l for COD. The sample are were use for 0.85 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.
8.0 REFERENCES
1. http://www.hbcse.tifr.res.in/protocol_guide.pdf 2. www.norweco.com/html/lab/test_methods/5220bfp.htm 3. www.pavloschemicals.com/lab 4. www.labseeker.com/labsupplies/lablist
