Biochemical Oxygen Demand (BOD) test: How to do

Summary

This video demonstrates how to conduct a 5-day Biochemical Oxygen Demand (BOD) test in a laboratory to measure the strength of organic matter in water samples. It explains the importance of BOD in assessing water contamination, the role of microorganisms in oxygen depletion, and the process for measuring BOD using a standard BOD bottle, dissolved oxygen meter, and incubator. The video also covers the preparation of dilution solutions and interpretation of results, including how to calculate the BOD value and determine whether the results are acceptable.

Takeaways

• 😀 The Beauty Test is a traditional method used to measure the strength of organic matter in water samples, helping assess water contamination.
• 😀 BOD stands for Biochemical Oxygen Demand, which quantifies the amount of oxygen consumed by microorganisms when decomposing organic matter in water.
• 😀 High concentrations of organics in water can lead to oxygen depletion, harming aquatic ecosystems.
• 😀 The Beauty Test measures oxygen consumption over time in a closed system to determine the degree of organic contamination in water.
• 😀 The Ultimate BOD (Ultimate Beauty or BDU) represents the total oxygen demand in the sample, and the 5-day BOD is a standard test period used for measurement.
• 😀 Essential equipment for the 5-day BOD test includes a BOD bottle, dissolved oxygen meter (DO meter), incubator set at 20°C, and dilution solutions for high-strength samples.
• 😀 A standard BOD bottle used for the test has a total volume of 300 ml, and its unique flared design ensures an airtight seal to prevent external oxygen interference.
• 😀 The BOD test procedure involves measuring the initial dissolved oxygen concentration, mixing the sample with a dilution solution, and incubating for 5 days.
• 😀 After 5 days, the change in dissolved oxygen concentration is measured again to calculate the 5-day BOD value.
• 😀 To calculate the 5-day BOD, the difference in dissolved oxygen concentration is divided by the dilution factor. If the concentration change is too low (less than 2 mg/L), the test result is considered unacceptable.
• 😀 In this example, a dilution factor of 0.05 was used, but the results did not meet the minimum acceptable change in oxygen concentration, meaning the sample was too diluted and further experiments were needed.

Q & A

What is the beauty test used for in water samples?

The beauty test is used to measure the strength of organic matter in water samples, which is an important parameter to determine water contamination by organics.

What does BOD stand for in the context of the beauty test?

BOD stands for Biochemical Oxygen Demand. It is used to measure the strength of organic matter in water.

Why is it important to measure organic contaminants in wastewater?

Organic contaminants in wastewater can damage the aquatic ecosystem by depleting oxygen levels in the water, as microorganisms consume these organics, leading to oxygen depletion.

How do microorganisms affect the oxygen levels in water?

Microorganisms consume organic materials in water, and this consumption leads to a decrease in the dissolved oxygen concentration over time.

What is the 'ultimate BOD' (BODu) in the beauty test?

The 'ultimate BOD' refers to the total amount of oxygen consumed by microorganisms to decompose the organic matter in the water sample, measured over a certain period.

What is the typical duration of the 5-day BOD test?

The 5-day BOD test typically lasts for 5 days at a controlled temperature of 20°C.

What are the key materials required for conducting the 5-day BOD test?

For the 5-day BOD test, you need a BOD bottle, an oxygen meter to measure dissolved oxygen (DO) levels, an incubator set to 20°C, and a dilution solution, especially for high-strength wastewater samples.

How is the dilution factor calculated in the BOD test?

The dilution factor is calculated based on the ratio of the wastewater sample to the dilution solution. For example, a 5% wastewater sample corresponds to a dilution factor of 0.05.

What criteria must be met for a valid BOD result?

For a valid BOD result, the change in dissolved oxygen concentration must be at least 2 mg/L, and the final DO concentration must be higher than 1 mg/L.

Why was the result of the 5-day BOD test in the video considered invalid?

The result was considered invalid because the change in dissolved oxygen concentration was only 0.53 mg/L, which did not meet the minimum required change of 2 mg/L. The sample was too diluted.

What should be done if the BOD test sample is too diluted to get valid results?

If the sample is too diluted, further experiments with less dilution should be conducted to obtain acceptable BOD values.