Biochemical Oxygen Demand Procedure: -

BOD stands for Biochemical Oxygen Demand. BOD is an important parameter used to measure the amount of oxygen required by microorganisms to break down the organic matter present in water. It is widely used to assess the pollution levels in water bodies and the effectiveness of wastewater treatment plants. In this article, we will discuss the step-by-step procedure for conducting the BOD test.

Materials Required: -

BOD bottles

BOD bottles

- Water sample

BOD water sample

- Sodium thiosulfate

- Manganese sulfate

Manganese sulfate

- Alkali-iodide-azide reagent

Alkali-iodide-azide reagent

- Sulfuric acid

Sulfuric acid

- Stirrer

Stirrer

- DO Meter

DO Meter

- Incubator

Incubator

Procedure: -

Step 1: Collect a representative sample of water from the water body to be tested. It is important to ensure that the sample is representative and free from any contamination during the collection process.

Step 2: Fill the BOD bottle with the water sample, leaving a small air gap to allow for expansion during the incubation period.

Step 3: Add a small amount of manganese sulfate to the BOD bottle to act as a nutrient for microorganisms. The amount added should be sufficient to provide nutrients but not so much that it affects the test results.

Step 4: Add a small amount of alkali-iodide-azide reagent to the BOD bottle. This reagent acts as a bactericide, preventing the growth of bacteria that are not involved in the BOD process.

Step 5: Add a small amount of sodium thiosulfate to the BOD bottle. This reagent is added to neutralize any residual chlorine present in the water sample, which can inhibit microbial respiration.

Step 6: Seal the BOD bottle with a stopper to prevent the entry of oxygen.

Step 7: Repeat steps 2 to 6 for at least three BOD bottles to obtain an average value for the BOD.

Step 8: Measure the initial dissolved oxygen (DO) level in the water sample using a DO meter.

Step 9: Incubate the BOD bottles at a specific temperature, usually between 20 and 25 degrees Celsius, for a period of five days.

Step 10: After the incubation period, measure the final DO levels in the BOD bottles using a DO meter.

Step 11: Calculate the BOD value as the difference between the initial and final DO levels. The BOD value is expressed in milligrams of oxygen consumed per liter of water (mg/L).

Step 12: Repeat the test for at least three BOD bottles to obtain an average BOD value.

Interpretation of Results: -

The BOD value obtained from the test indicates the amount of oxygen consumed by microorganisms to break down the organic matter present in the water sample. Higher BOD values indicate the presence of more organic matter, which can lead to the growth of harmful algal blooms and oxygen depletion in water bodies.

The BOD value can also be used to determine the biodegradable fraction of organic matter in water. The biodegradable fraction refers to the portion of organic matter that can be broken down by microorganisms, leading to the release of nutrients such as nitrogen and phosphorus. These nutrients can promote the growth of aquatic plants and algae, leading to eutrophication, a process where the water body becomes excessively rich in nutrients, leading to the growth of harmful algal blooms and oxygen depletion.

Conclusion: -

BOD testing is an important aspect of water quality monitoring and is widely used to assess the pollution levels and health of water bodies. The procedure for conducting the BOD test involves collecting a representative water sample, adding reagents to neutralize any residual chlorine, preventing the growth of bacteria, and measuring the initial and final DO levels to calculate the BOD value. 

Also Read - 

What is BOD | Characteristics of BOD | Advantages and Disadvantages of BOD | Importance of BOD.

BOD Incubator | BOD Incubator full form | BOD Incubator uses | BOD Incubator working principle | BOD Incubator temperature range | BOD Incubator operation.

BOD Principles | Factors Affecting BOD | Importance of BOD

Biochemical Oxygen Demand Measures