Chemical Oxygen Demand

1. INTRODUCTION

Chemical oxygen demand (COD) is define as amount of a specified oxidant that reacts with the sample under controlled conditions. The quantity of  oxidant consumed is expressed in terms of its oxygen equivalence. Because of its unique chemical properties, the dichromate ion is the specified oxidant. Both organic and inorganic components of a sample are subject to oxidation but in most cases the organic component predominates and is of the greater interest.

In a COD analysis, hazardous wastes of mercury, hexavalent chromium, sulfuric acid, silver and acids generated. Methods 5220C and D reduce these water problems but may be less accurate and less representative.

1. OBJECTIVE

1. The measurement the chemical of oxygen demand (COD) of solid, or liquid organic substances in a standard, arbitrary manner, under fixed laboratory conditions.
2. The measurement of pollutants in wastewater  and natural waters.

1. THEORY

The amount of oxygen dissolved in water is important to aquatic life. Decaying matter in sewage, industrial discharged, agricultural and urban runoff uses up the dissolved oxygen in water. The chemical oxygen demand (COD) is a measure of the amount is chemicals             ( usually organic ) that consume dissolved oxygen.

Water quality standards for dissolved oxygen are set by state regulations to protect aquatic life. Many lakes and streams across the country do not meet these standards. Improving the quality of water means controlling or improving agricultural practices, revegetating stream-banks, and controlling storm water. For those areas affected by industrial wastewater , improvements in wastewater purification are necessary.

1. APPARATUS

DR 600

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Glove

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Pipette  Filler Safety Bulb

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Test Tube Rack

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DRB200 Reactor                                                            

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Chemical Reagent (Blank and Sample)

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Beaker

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   Glass Bottle        

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1. PROCEDURE

1. The blank sample was prepared.
2. 2.00 ml was added into the sample to the vial using a clean pipette .

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1. The vials is tightly closed. Then, the vials was rinse with water and wipe with a clean paper towel.
2. The vials was put in the preheated DRB200 reactor. The vial was heated for 2 hours.

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1. Switch off the reactor power and  the vials was cooled in the reactor for 20 minutes.

1. The vials were put in tube rack for cooling to room temperature.

1. Start program 431 COD ULR, 430 COD LR or 435 COD HR.

1. The blank sample cell was cleaned using a piece of tissue.

1. Inserted the blank into the cell holder.

1. Push ZERO. The display shows 0 or 0.0 mg/L COD.

1. Inserted the prepared sample into the cell holder.

1. Push READ. Results show in mg/L COD.

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