CEEB 221 INTRODUCTION TO ENVIRONMENTAL ENGINEERING LABORATORY

LABORATORY EXPERIMENT NO. 7

(Chemical Oxygen Demand) COD MEASUREMENT

SECTION: 05

NAME IDMUHAMMAD FIKRIL AZIM BIN ABDUL SANI CE094946

AMMAR BIN MD DENI CE095821JULIANA BINTI RAZALI CE095999

DATE OF LABORATORY SESSION : 4 DECEMBER 2015

DATE OF REPORT SUBMISSION : 11 DECEMBER 2015

LAB INSTRUCTOR : ENCIK NAZIRUL MUBIN BIN ZAHARI

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TABLE OF CONTENT

CONTENT PAGE

Table of Content 2

Summary/Abstract 3

Introduction & Objective 3

Apparatus and Equipment 4

Procedure 4

Results 5

Discussion 5-6

Conclusion 6

References 6

Appendix 7-8

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Summary/Abstract

Chemical Oxygen Demand (COD) is the standard method for indirect measurement of the amount of pollution (that cannot be oxidized biologically) in a sample of water.

The chemical oxygen demand test procedure is based on the chemical decomposition of organic and inorganic contaminants, dissolved or suspended in water. The result of a chemical oxygen demand test indicates the amount of water-dissolved oxygen (expressed as parts per million or milligrams per liter of water) consumed by the contaminants, during two hours of decomposition from a solution of boiling potassium dichromate.

The higher the chemical oxygen demand, the higher the amount of pollution in the test sample. For the contaminants that can be oxidized biologically, the biological oxygen demand (BOD) method is used.

Introduction

The standard BOD test involves placing a small amount of sample into a standard BOD bottle of capacity 300ml. Then it is incubated for standard 5 days. The drawback of this method is that it takes 5 days to obtain a result. Another method is to measure chemical oxygen demand or COD of the sample.

COD test measures the oxygen required to oxidize all the organic matter in the sample using acid. It takes about 2 hours to complete the test. The reagents will react over 120 minutes at 150 C, since it is not easyto estimate the COD concentration, for initial test, two reagent range are used ( low range and high range ). Since this is an acid reacted test, it is very important to follow safety procedure strictly-must wear goggles and rubber glove and lab coat to prevent accidental spillage.

Objective

To measure the COD of a sample.

Apparatus

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The list of apparatus includes:

- Spectrophotometer

- Pipettes

- Reagents in a vial

- Reactor at 150 C

- Distilled water

Procedure

1. A sample of 2 ml was pipette into low range vial, mixed and transfer to a reactor

2. Distilled water was pipetted 2 mil into the another low range vial, mix and transfer to a reactor.

3. 2 ml of sample was pipetted into high range vial, mixed and transfer to a reactor.

4. Distilled water was pipetted 2 mil into the another high range vial, mix and transfer to a reactor.

5. The vials was heat up for 120 minutes at 150

6. After 120 minutes, the vials was cooled by placing under the running tap water.

7. Once they are cooled, use spectrophotometer to measure the COD concentration

8. Choose the right program ( at low range ) at spectrophotometer, insert vial with distilled water and zeroing. After that, the sample was inserted and read result on the spectrophotometer.

9. Similarly, change the program to high range and step 8 was repeated.

Results

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Sample COD reading at low range (mg/L) COD reading at high range (mg/L)

A 27 114

Discussion

The Chemical Oxygen Demand (COD) test is commonly used to indirectly measure the amount of organic compound in water, most applicable 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. It is expressed in milligrams per liter (mg/L), which indicates the mass of oxygen consumed per liter of solution.

COD is the measurement of the amount of oxygen in water consumed for chemical oxidation pollutants.

COD determine the quantity of oxygen required to oxidize the organic matter in water or waste water sample, under specific condition of oxidizing agent, temperature, and time.

This method covers the determination of COD in ground and surface waters, domestic and industrial waste water. The applicable range is 3-900 mg/l

These are the some errors or mistakes that we have done in the experiment. Sometimes the sample may be toxic to the bacteria, or seed, that break down the wastes. This is often seen as decreasing COD results on a sample coinciding with decreasing dilution rates.

Good sampling is necessary if laboratory testing is to be accurate. The sample must be representative, collected properly, handled carefully and preserved correctly. No matter how accurate the actual testing is, if the sample is not representative, the results of the test will be misleading and can lead to poor plant performance. Samples for COD analysis may change greatly during handling and storage.

Testing should be started as quickly as possible. Sometimes waters, particularly those containing high concentrations of algae, maybe ‘supersaturated’ with dissolved oxygen (that is, due to pure oxygen production by algae during photosynthesis, the water has a higher concentration of oxygen than normal saturation value). If this is the case, the sample should be shaken in a partially filled bottle so that all excess oxygen is lost before the COD analysis takes place. If such a procedure is not carried out, the excess oxygen may be lost during the COD test leading to an incorrect result.

Therefore, in order to get the accurate and better result, we need to overcome these errors by following some steps. Firstly, we need to consider the sampling location. Care must be taken to make sure the sample is representative of the water body from which the sample was

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taken. Besides, we need to consider about the sample size. Samples should be taken in a clean plastic or glass container of sufficient size to provide enough samples for all of the tests and the quantity of COD bottles that will be incubated for that sampling site. Another consideration in determining sample size is that the sample must be representative of the waste stream, and the smaller the sample, the more difficult it is to make sure that it is representative. Followed by preservation and holding times. In most environmental samples, bacteria naturally present in a waste stream are consuming oxygen before, during and after the sample is taken. Therefore, starting the analysis as soon after taking the sample is very important

Conclusion

After conducting this experiment, we can clearly see that the COD reading at low range & COD reading at high range showed different readings. In a conclusion, the value of COD

obtained from this experiment for High Range is 114 mg/L and 27 mg/L for Low Range. The value indicates the chemical reactivity against the samples, and the result shows that the objective of this experiment is achieved.

References

Laboratory Manual, CEEB 221 Introduction to Environmental Engineering Laboratory, 1st draft October 2013 by CKH.

http://www.businessdictionary.com/definition/chemical-oxygen-demand-COD.html#ixzz3tUmQpxmp

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Appendix

High Range and Low Range Chemicals

Placing the mixture of HR and LR with samples in the reactor for 2 hours

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Distilled water pipetted into sample

Reading the spectrophotometer

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