Experiment COD

Bachelor of Science (Hons) (Applied Chemistry) (AS 225)

LABORATORY REPORT

Water and Wastewater Technology (CMT564) Experiment Name Name of Partners

Demonstrator OBJECTIVES:

5 : Chemical Oxygen Demand (COD) Hanim Binti Ismail 2009401538 Norhazwani Binti Zubairi 2009659246 Norezzati Afifa Bt Razali 2009258728 Norhaniza Bt Hamzah Mr. Lee Kok Kheng

2009902677

To measure the Chemical Oxygen Demand (COD) of the sample using Reactor Digestion Method and calculate the percentage of the COD reduction for the sample.

RESULT: Group

COD of raw wastewater (mg/L) 1 OR 2 5715 3 5680 4 OR CALCULATION:

COD of treated water (mg/L) 461 735 402 700

% COD reduction 92.31 % 91.93 % 92.92 % 88.33 %

COD of standard (mg/L) UR 135 60 135

% COD reduction = COD of raw wastewater - COD of treated water x 100 COD of raw wastewater Example of the calculation : % COD reduction = 5715 – 461 x 100 5715 = 91.93 % COMMENT : Reactor Digestion Method is used in this experiment to shorten the traditional dichromate reflux method time. From the result, the COD of the raw wastewater measured is over range (OR), it is because the sample that we use is in excessive amount, therefore the spectrophotometer cannot detect the reading. To calculate the percentage of COD reduction for group1 and 4, we choose to use 6000 mg/L replacing the OR value since the COD of other group is above 5500mg/L. By comparing the result group 2 and 3, the COD of raw wastewater is close to each other and got a large number. It can be said that the water is content of large amount of carbon in insoluble organic. Based on the result, the COD of treated water is lower than raw wastewater because it has been treated well and less carbon content of soluble organic matter in the water. The COD of standard is lower that the treated because standard we used is the deionised water which contains less oxidized inorganic material. Because COD measures the oxygen demand of organic compounds in a sample of water, it is important that no outside organic material be accidentally added to the sample to be measured. To control for this, a so-called blank sample is required in the determination of COD. A blank sample is created by adding all reagents (e.g. acid and oxidizing agent) to a volume of distilled water. COD is measured for both the water and blank samples, and the two are compared. The oxygen demand in the blank sample is subtracted from the COD for the original sample to ensure a true measurement of organic matter. Some samples of water contain high levels of oxidized inorganic materials which may interfere with the determination of COD. Because of its high concentration in most wastewater, chloride is often the most serious source of interference. This interference can be eliminated by the addition of mercuric sulfate to the sample, prior to addition of other chemicals. The mercuric ion combines with the chloride ion to form a poorly ionized mercuric chloride complex.

There are several errors occur while doing the experiment. The largest error is caused by using a non homogeneous sample. Every effort should be made to blend and mix the sample so that solids are never excluded from any aliquot. There are several precaution in this experiment that we should followed, since the vials contain sulphuric acid, potassium dichromate, silver and mercury, it must be handled properly and not to through away the solutions into the laboratory sink because mercury is very hazardous. We have to careful when take out the vials from the COD reactor because they are heated to 150oC and become very hot. CONCLUSION: From this experiment, the COD of the raw wastewater, treated water and the standard is measured. The COD of the raw wastewater is greater than COD of the treated water and COD of the standard is the smallest. The percentage of reduction of the COD is above 90% QUESTION: 1) What was the purpose of the blank sample of distilled water? Because COD measures the oxygen demand of organic compounds in a sample of water, it is important that no outside organic material be accidentally added to the sample to be measured. To indicate the absence of contamination or super saturation of dilution water with DO. 2) Why is it important to determine COD test in wastewater treatment? COD is a measurement of the maximum organic load and this indicates the type of treatment needed and if doing the treatment biologically, the amount of oxygen required doing it. In effluent, it is related to the pollution level, but there are many factors included in that determination. There are different COD tests and each has to be interpreted a different way. Hg/Cr COD gives the max number, while Mn COD will be closer to the BOD measurement. 3) Summarize the method and write the chemical reaction involved and interpret your test result?

A catalyst, silver compound is added to promote the oxidation of certain classes of organics, and a mercuric compound may be added to reduce interference from the oxidation of chloride ions by the dichromate. End products are carbon dioxide, water, and various states of the chromium ion. After the oxidation step is completed, the amount of dichromate consumed is determined by measuring its absorbance. In the oxidation of organic materials by dichromate in sulfuric acid, most of the carbon is converted to carbon dioxide while any hydrogen present in the organic compound is converted to water. Other elements also may be oxidized. A blank is also prepared to ‘zero’ (to calibrate) the spectrophotometer. The COD value is directly displayed in the window of the instrument. The chemical equation involved is: 4) A sample is collected for COD analysis and it is to be performed on the following day. Describe two ways by which the sample can be preserved. 2 ways to preserve the sample is by adding sulfuric acid, H2SO4 as the preservative and adjust the pH