COD Lab Report full

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 95-100% the theoretical value.

4.0 EQUIPMENT I.

II. III. IV.

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. Burette Pipette COD vial

4.1 REAGENT I.

Standard potassium dichromate 0.016667M 1000ml distilled water 4.903g potassium dichromate (K2 CR2 O7) dry 2 hour 150 ‫ﹾ‬C 167ml' acid sulphuric (H2 SO4) 33.3g mercury sulphate (Hg SO4).

II.

Sulphuric acid reagent 5.5g silver sulphate (Ag SO4) 1kg acid sulphuric (H2 SO4)

III.

Standard ferrous ammonium sulphate 39.2g ammonium iron II sulphate 6-Hydrate {Fe (NH4)2(SO4)2. 6H2o} 20ml acid sulphuric (H2 SO4) 1L distilled water 0.)

IV.

Ferroin indicator

5.0 PROCEDURE 5.1 Standard Method 5220 C 5.2 Sampling Procedure I. II. III.

The sample is collected in plastic container that is known no organic contamination in the container. The sample is tested biologically Sample is preserved with sulphuric acid to a pH value < 2

5.3 Laboratory Procedures 1) The substances were added in COD vial by followed the sequences below: a) Placed in COD vial 1 and 2 with: 1.5 ml Potassium Dichromate Reagent 3.5 ml Acid Sulphuric Reagent b) COD vial no.1: 2.5 ml sample

COD vial no.2: 2.5 ml distilled water

2) Refluxing mixture placed at COD Reactor with temperature 150 ‫ﹾ‬C for 1 hour.

3) After 1 hour, cool down the condenser with distilled water. Cooling down process continued to room temperature. 4) Disconnect reflux condenser. The solution transferred to the conical flask and mixed up with 150ml distilled water. Added with 3 drops of ferroin indicator. 5) Titrated K2 Cr2 O7 with Ferrous Ammonium Sulfate (FAS). The initial and final reading recorded. The titration stopped when colour changed into reddish brown.

5.4 Titration Test 1) 5ml Postassium Dichromate K2 Cr2 O7 solution (0.01667 M) diluted with 10ml of distilled water into 250ml conical flask. Swirled and mixed slowly. 2) 30ml of concentrated acid sulfuric H2SO4 was added slowly and carefully. Titrated with FAS titrant using 3 drops of ferroin indicator. The titration is stopped immediately when the colour changed into reddish brown. 3) Initial and final reading was recorded.

6.0 RESULT Table 1: FAS standard titration data: Reading of buret/pipette First reading Last reading Volume of FAS (ml)

Cone flask (Standard) 0 5.6 5.6

6.1 Compute the molarity of FAS by using the given formula: Molarity of FAS solution=

Volume 0.1667 M K 2Cr 2O 7 solutiontitrated , ml X 0.100 Volume FAS used ∈titration , ml

Molarity of FAS solution=

5.0 X 0.100 5.6

Molarity of FAS solution=0.089 Table 2: COD test data collections: Normality of FAS (N)

Sample volume (ml)

0.1

2.5

Volume of FAS used In the original In the blank sample, b (ml) sample, s (ml) 3.2 4.0

6.2 Compute the COD concentration in mg/L for the sample by using the given fprmula: COD as mg/ L=

( A−B ) X M X 8000 ( ml ) sample

COD as mg/ L=

( 4−3.2 ) X 0.089 X 8000 2.5

COD as mg/ L=227.8 mg/ L

7.0 ANALYSIS 1) Which volume is larger, in the blank sample or in original sample Based on the result obtained, the blank sample has the larger volume which is 4.0ml compared with original sample which has 3.2 ml of volume 2) How to obtain the normality of FAS equal 0.25N Normality of FAS=

W eight of potassium dichromate taken ( V olume of ferrous ammonium sulphate solution ) X 0.04904 X 10 consumed∈titration

3) If the original sample has to be diluted, how can you calculate the COD value By using the formula: COD as mg/ L=

( A−B ) X M X 8000 ( ml ) sample

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. 2. 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. 3. 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 matter 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. 4. Give your opinion if you need to compare the results of COD test to BOD and permanganate value (test COD by using potassium permanganate, KMnO4) tests. In my opinion, PV and COD are a measure of the amount of reduced compounds in a sample, which have been oxidized by a strong oxidizing agent. Although inorganic substances such as Fe2+, S2- may also be subject to oxidation for most natural and industrial waters, the matter to be oxidized is organic in nature. Therefore these values can be used to characterize the organic load of water. For COD determinations, the

organic matter is almost completely oxidized (conversion >90%) due to the stringent oxidizing conditions (K2 Cr2 O7 in excess 2 hours, 150 ‫ﹾ‬C, catalyst Ag). Moreover the permanganate test is a much milder (KMnO4, 10 min, 120 ‫ﹾ‬C) and only the readily-oxidizable compounds will be converted. Conversion is only around 30%-50% for natural waters with industrial waters conversions vary even more (10%-80%).The BOD characterizes the biological biodegradability and is closely related to the PV, as it describes this part of the COD that is more readily oxidized. Depending on the type of water, the BOD, (biodegradability in 5 days, expressed as ppm O2) from 0.5 up to 3 times the PV (as ppm O2), and for most waters a value of 1.5 can be applied. 5. Why the value of COD increases when the amount of pollutant increased in surface water. Because there is contain ammonia in surface water that can be organic origin, the product of decomposition plant and animal matter, or of inorganic origin, formed due to chemical or biochemical reduction of nitrate and nitrite. Ammonia is a very unstable compound and easily undergoes nitrification. Ammonia is an indicator of pollution originating from soil (the excessive use of ammonarichnfertelizers) atmosphere and sewage.

6. Explain briefly the steps of COD measurement that you should follow during this experiment.    

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2.5ml of sample poured into test tube which contain 1.5ml of potassium dichromate reagent and labelled as test tube 1. 2.5ml of distilled water poured into test tube which contain 3.5ml acid sulfuric reagent and labelled as test tube 2. Both of the test tube mixed up properly and placed in COD Reactor with temperature 150 ‫ﹾ‬C for 1 hour. After 1 hour, cooling down both of the test tube before pouring into conical flask. Put the sample into conical flask and conical flask 1 and conical flask 2 labelled. Test tube 1 and test tube 2 added with distilled water and swirled two times and poured into conical flask prepared. 3 drops of ferroin indicator added into each of the conical flask Then, both of the solution titrated with K2 Cr2 O7 with Ferrous Ammonium Sulfate (FAS) until the colour changed into reddish brown. Initial and final reading recorded

7. Briefly explain whether the value of COD obtain in this experiment are suitable to be discharged to the stream. Discharge COD limits can be different with different waste streams (from specific industries) and COD limit values can be between 100 to 350mg/L depending on the waste stream. Based on the result obtained, 227.8 mg / L is suitable to be discharged to the stream.