10 Differences Between bod and cod

BOD vs COD: Understanding the Key Differences

Intro: When it comes to measuring water quality, two common terms that often come up are BOD (Biochemical Oxygen Demand) and COD (Chemical Oxygen Demand). Both BOD and COD play a crucial role in assessing the level of organic pollutants in water bodies. In this article, we will explore the definitions, examples, uses, and crucial differences between BOD and COD.

What is BOD?

BOD, or Biochemical Oxygen Demand, is a measure of the amount of oxygen required by microorganisms to degrade organic matter in water. It is an essential parameter used to evaluate the organic pollution level in natural waters and wastewater.

Examples of BOD:

– Domestic sewage waste

– Industrial wastewater with organic content

– Agricultural runoff with organic pollutants

Uses of BOD:

– Determine the quality and freshness of water bodies

– Assess the effectiveness of wastewater treatment plants

– Identify the impact of pollutants on aquatic life

– Determine compliance with environmental regulations

What is COD?

COD, or Chemical Oxygen Demand, is a measure of the amount of oxygen required to chemically oxidize organic and inorganic substances in water. Unlike BOD, COD determines both the biodegradable and non-biodegradable organic content present in the water sample.

Examples of COD:

– Industrial effluents rich in various organic and inorganic compounds

– Agricultural runoff containing pesticides and fertilizers

– Municipal and domestic wastewater with a mix of chemicals and organics

Uses of COD:

– Assess the pollution load in water bodies

– Determine the efficiency of sewage treatment plants

– Monitor industrial wastewater discharge compliance

– Evaluate the impact of chemicals on aquatic ecosystems

Differences Between BOD and COD:

Difference Area BOD COD
Definition A measure of oxygen required by microorganisms to degrade organic matter in water. A measure of oxygen required to chemically oxidize both organic and inorganic substances in water.
Biodegradability Determines only biodegradable organic content. Determines both biodegradable and non-biodegradable organic content.
Test Duration It usually takes several days (5 – 20 days) to complete the test. The COD test can be completed within a few hours.
Sample Handling BOD samples require special handling and preservation techniques to prevent bacterial growth and oxygen consumption. COD samples are relatively stable and easy to handle without strict preservation requirements.
Measurement Time Requires an extended time for measurement due to microbial degradation. Requires less time for measurement as it relies on chemical oxidation.
Sensitivity The BOD test is less sensitive to some toxic substances and certain types of inorganic compounds. The COD test is more sensitive to various toxic and complex organic compounds.
Cost and Equipment Generally, BOD tests require a longer incubation period and specialized equipment, making them more expensive. COD tests are relatively less expensive as they require simpler equipment and yield quicker results.
Environmental Conditions Microbial activity during BOD tests is influenced by temperature, pH, and environmental factors. COD tests are less influenced by environmental conditions, providing more consistent results.
Organic Matter Type BOD measures primarily biodegradable organic matter. COD measures both biodegradable and non-biodegradable organic matter, as well as inorganic compounds.
Regulatory Standards BOD values are widely used to regulate discharges into water bodies. COD is more commonly used to regulate industrial effluents.


In summary, both BOD and COD play crucial roles in assessing water quality and pollution levels. While BOD focuses on measuring the oxygen required by microorganisms to degrade organic matter, COD determines oxygen demand through chemical oxidation of organic and inorganic substances. BOD tests are more suitable for biological treatment evaluation, while COD tests are effective in assessing industrial pollution. Understanding these key differences helps in selecting the appropriate method for water quality assessment and regulatory compliance.

People Also Ask:

Q: How do BOD and COD affect aquatic life?
A: High BOD and COD levels in water bodies deplete oxygen, causing stress or death to aquatic organisms.

Q: Which test, BOD or COD, is better for wastewater treatment evaluation?
A: BOD is more suitable for evaluating biological treatment processes, while COD provides a broader measure of total oxygen demand.

Q: Can BOD and COD measurements be done simultaneously?
A: Yes, it is possible to measure BOD and COD simultaneously using specific laboratory techniques.

Q: Do BOD and COD values always correlate?
A: Though BOD and COD values are related, they may not always correlate due to differences in organic matter composition and biodegradability.

Q: Are BOD and COD values used in water quality regulations?
A: Both BOD and COD values are widely used in environmental regulations to ensure water bodies’ health and prevent pollution.

Leave a Comment

content of this page is protected

Scroll to Top