Courses
Courses for Kids
Free study material
Offline Centres
More

Difference Between BOD and COD

ffImage
Last updated date: 22nd Feb 2024
Total views: 69.3k
Views today: 1.69k

Explaining BOD and COD: An Introduction

In environmental and wastewater management, two critical parameters used to assess water quality and pollution levels are Biological Oxygen Demand (BOD) and Chemical Oxygen Demand (COD). These measures provide valuable insights into the organic pollution present in water bodies and help determine the effectiveness of water treatment processes. This article aims to explore and compare BOD and COD, highlighting their definitions, measurement methods, significance, and differences in applications.


Definition of BOD

Biological Oxygen Demand (BOD) is a measure of the amount of dissolved oxygen consumed by microorganisms during the biological breakdown of organic matter in water. It indicates the level of organic pollution and the microbial activity in an aquatic ecosystem. BOD is expressed in milligrams of oxygen per liter (mg/L) and is typically determined by measuring the oxygen consumed over a specific period, often five days (BOD₅).


Definition of COD

Chemical Oxygen Demand (COD) is another measure used to determine the amount of organic matter present in water. Unlike BOD, COD measures the oxygen equivalent required to chemically oxidize both biodegradable and non-biodegradable organic substances in water. It quantifies the total organic load in a water sample, including both readily and slowly biodegradable compounds. COD is also expressed in milligrams of oxygen per liter (mg/L).

Characteristics of BOD and COD

Measurement

The measurement of BOD involves collecting a water sample and incubating it in a controlled environment for a specific duration, usually five days, at a constant temperature (usually 20°C). During this incubation period, microorganisms present in the water consume the organic matter, utilising dissolved oxygen in the process. After incubation, the remaining dissolved oxygen is measured using an oxygen sensor or titration methods. The difference in dissolved oxygen concentrations before and after incubation represents the BOD value.


The measurement of COD involves the chemical oxidation of organic compounds in a water sample using strong oxidizing agents, such as potassium dichromate (K₂Cr₂O₇) or potassium permanganate (KMnO₄). This oxidation process converts the organic matter into carbon dioxide and water. The amount of oxidising agent consumed in the reaction is then measured, providing the COD value. Various analytical methods, such as reflux and titration, spectrophotometry, or colorimetry, are employed to determine the concentration of the oxidising agent before and after the reaction.


Significance of BOD and COD 

BOD serves as an important indicator of the organic pollution level in water bodies. High BOD values indicate the presence of substantial amounts of biodegradable organic substances, such as sewage, agricultural runoff, or industrial wastewater, which can deplete dissolved oxygen levels. This oxygen depletion poses a threat to aquatic life, as low oxygen concentrations can lead to hypoxia and harm or even kill fish and other organisms. Monitoring BOD helps in assessing the health of water bodies, identifying pollution sources, and determining the effectiveness of wastewater treatment processes.


COD serves as a valuable parameter in assessing the overall organic pollution load in water bodies. Unlike BOD, which measures only biodegradable organic matter, COD provides a comprehensive measure of both biodegradable and non-biodegradable organic substances. It helps identify the presence of pollutants that may not be readily biodegradable and could persist in the environment. Monitoring COD aids in evaluating the efficiency of wastewater treatment processes and determining the need for additional treatment or pollution control measures.


Explaining the Difference Between BOD and COD 

Aspect

BOD 

COD 

Definition

Measure of oxygen consumed by microorganisms during biological degradation of organic matter.

Measure of oxygen equivalent required for chemical oxidation of both biodegradable and non-biodegradable organic matter.

Measurement

Requires incubation of water samples for a specific duration (typically five days) at a constant temperature.

Involves chemical oxidation of organic compounds in a water sample using strong oxidising agents.

Time

Takes several days for the incubation period.

Can be measured relatively quickly, often within a few hours.

Biodegradability

Specifically measures biodegradable organic matter.

Measures both biodegradable and non-biodegradable organic substances.

Sensitivity

More sensitive to easily degradable organic compounds.

More sensitive to complex organic compounds that are resistant to biological degradation.

Application

Used to assess the level of organic pollution, microbial activity, and treatment efficiency.

Provides a comprehensive assessment of the overall organic pollution load and aids in designing treatment processes and pollution control strategies.


Conclusion

BOD and COD are essential parameters in assessing water quality and organic pollution levels. BOD measures the oxygen consumed by microorganisms during biological degradation, reflecting the biodegradable organic matter, while COD measures the oxygen equivalent required for the chemical oxidation of both biodegradable and non-biodegradable substances. Understanding the differences between BOD and COD is crucial for effective environmental management, wastewater treatment, and pollution control strategies. By employing these parameters, researchers, environmentalists, and policymakers can make informed decisions to protect and preserve our water resources.

FAQs on Difference Between BOD and COD

1. What is COD and BOD?

COD (Chemical Oxygen Demand) measures the oxygen equivalent required for the chemical oxidation of both biodegradable and non-biodegradable organic substances in water. On the other hand, BOD (Biological Oxygen Demand) measures the oxygen consumed by microorganisms during the biological breakdown of organic matter.

2. How are COD and BOD Measured?

COD is typically measured by chemically oxidising organic compounds in a water sample using strong oxidizing agents, such as potassium dichromate or potassium permanganate. The amount of oxidizing agent consumed in the reaction is then measured. BOD, on the other hand, is measured by incubating a water sample under controlled conditions for a specific duration, often five days, and measuring the oxygen consumed by microorganisms during this period.

3. What are the Applications of COD?

COD Provides a comprehensive assessment of the overall organic pollution load and aids in designing treatment processes and pollution control strategies.