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Biochemical Oxygen Demand vs. Chemical Oxygen Demand: What's the Difference?

Edited by Aimie Carlson || By Janet White || Published on February 14, 2024
Biochemical Oxygen Demand (BOD) measures organic pollution biologically decomposed over time, whereas Chemical Oxygen Demand (COD) quantifies all organic matter chemically oxidizable, including biologically resistant compounds.

Key Differences

Biochemical Oxygen Demand (BOD) is a measure of the amount of oxygen that microorganisms require to break down organic matter in water. Chemical Oxygen Demand (COD), in contrast, assesses the total quantity of oxygen needed to chemically oxidize all organic and inorganic substances in water. BOD focuses on biodegradable organic matter, while COD encompasses both biodegradable and non-biodegradable compounds.
In the context of water pollution, Biochemical Oxygen Demand is crucial for estimating the effect of effluent on the receiving waters. It reflects the amount of organic pollution susceptible to biological degradation. On the other hand, Chemical Oxygen Demand is a broader measure, providing an overall picture of the amount of pollutants present in water, including those not readily biodegradable.
Biochemical Oxygen Demand testing typically involves incubating a water sample for five days at 20°C and measuring the oxygen depletion. It’s sensitive to temperature and microbial activity. Chemical Oxygen Demand uses strong chemical oxidants in a much shorter timeframe, often just a few hours, to break down substances, giving a faster assessment of water quality.
When monitoring wastewater treatment processes, Biochemical Oxygen Demand is essential for understanding the biological treatment stage's effectiveness. Chemical Oxygen Demand, however, is often used for assessing the efficiency of both biological and chemical treatment processes, providing a more comprehensive overview of the treatment's efficacy.
For environmental compliance, both BOD and COD are important. Biochemical Oxygen Demand is often used to assess compliance with regulations regarding the discharge of biodegradable materials. In contrast, Chemical Oxygen Demand can be used for more general water quality assessments, including the presence of both biodegradable and non-biodegradable pollutants.

Comparison Chart


Organic pollution biologically decomposed over time
All organic matter chemically oxidizable


Microbial oxygen consumption
Chemical oxidation

Time Frame

Typically 5 days at 20°C
Often a few hours

Pollutant Type

Primarily biodegradable organic matter
Both biodegradable and non-biodegradable matter


Estimating effect of effluent on receiving waters
Broad assessment of water quality

Biochemical Oxygen Demand and Chemical Oxygen Demand Definitions

Biochemical Oxygen Demand

Measurement of oxygen used by microorganisms to decompose organic matter in water.
High Biochemical Oxygen Demand indicates severe pollution in a river.

Chemical Oxygen Demand

A measure of water's total chemical oxidizable content, indicating pollution level.
A high Chemical Oxygen Demand in the river pointed to industrial contamination.

Biochemical Oxygen Demand

Estimation of the oxygen required to biologically oxidize organic waste in water.
The city's sewage treatment plant monitors Biochemical Oxygen Demand to control pollution.

Chemical Oxygen Demand

Quantification of oxygen needed to chemically oxidize all organic substances in water.
The Chemical Oxygen Demand of the effluent was alarmingly high.

Biochemical Oxygen Demand

Indicator of the amount of biodegradable organic material in water.
The Biochemical Oxygen Demand of the lake water increased after the industrial spill.

Chemical Oxygen Demand

A chemical method to determine the organic pollution load in water.
Wastewater's Chemical Oxygen Demand is often tested before and after treatment.

Biochemical Oxygen Demand

A gauge of the organic pollution load in wastewater.
Treating wastewater effectively reduces its Biochemical Oxygen Demand.

Chemical Oxygen Demand

Measurement of oxygen equivalent of organic matter susceptible to oxidation by strong chemical oxidants.
The factory's waste showed a significant Chemical Oxygen Demand, indicating high pollution.

Biochemical Oxygen Demand

A measure of oxygen depletion caused by aerobic biological activity in water.
The Biochemical Oxygen Demand test showed the river's deteriorating water quality.

Chemical Oxygen Demand

Assessment of both biodegradable and non-biodegradable organic matter in water.
Chemical Oxygen Demand analysis helps in evaluating comprehensive water treatment processes.


What is Biochemical Oxygen Demand?

A measure of the amount of oxygen microorganisms need to decompose organic material in water.

What does Chemical Oxygen Demand indicate?

It indicates the total quantity of oxygen required to oxidize all organic substances in water, both biodegradable and non-biodegradable.

Can Biochemical Oxygen Demand be used to assess water pollution?

Yes, it’s a key indicator of organic pollution levels, especially in natural water bodies.

What is the significance of Chemical Oxygen Demand in water treatment?

It helps in assessing the overall effectiveness of water treatment processes by measuring the reduction in organic pollutants.

Does high Biochemical Oxygen Demand mean poor water quality?

Generally, yes. High BOD indicates high levels of biodegradable organic material, which can deplete oxygen and harm aquatic life.

Does Chemical Oxygen Demand include biologically resistant compounds?

Yes, it includes compounds that are resistant to biological degradation.

How is Biochemical Oxygen Demand measured?

By assessing the reduction in oxygen concentration over a set period, typically five days, at a specific temperature (20°C).

Can Chemical Oxygen Demand measure inorganic substances?

Yes, it can measure the oxidizable inorganic substances, unlike BOD which focuses only on organic matter.

Is Chemical Oxygen Demand testing faster than Biochemical Oxygen Demand?

Yes, COD testing typically takes a few hours, compared to the five-day incubation period for BOD testing.

What are common applications of Chemical Oxygen Demand testing?

Monitoring water pollution, assessing effluent quality, and checking the efficiency of wastewater treatment processes.

How does Biochemical Oxygen Demand impact aquatic life?

High BOD can lead to oxygen depletion in water, adversely affecting aquatic organisms.

What factors affect Biochemical Oxygen Demand levels?

Factors include temperature, microbial activity, and the amount of organic matter present.

Why is Chemical Oxygen Demand important in industrial settings?

It provides a quick assessment of the pollution load in industrial effluents and helps in regulatory compliance.

Is Biochemical Oxygen Demand testing temperature-sensitive?

Yes, the microbial activity involved in BOD testing is influenced by temperature.

What is the primary use of Biochemical Oxygen Demand testing in wastewater treatment?

To evaluate the effectiveness of biological treatment stages in reducing organic pollution.

How does Chemical Oxygen Demand help in environmental regulation compliance?

It provides a comprehensive measure of all oxidizable pollutants, aiding in meeting environmental discharge standards.

What does a low Biochemical Oxygen Demand indicate?

It suggests low levels of biodegradable organic pollution, which is typically favorable for water quality.

Can both Biochemical Oxygen Demand and Chemical Oxygen Demand be high in a sample?

Yes, if there is a high concentration of both biodegradable and non-biodegradable pollutants.

Are Biochemical Oxygen Demand and Chemical Oxygen Demand always correlated?

Not necessarily, as BOD measures only biodegradable organic matter while COD includes more compounds.

Can Chemical Oxygen Demand be used to predict Biochemical Oxygen Demand?

To some extent, but not accurately, as COD includes substances not measured by BOD.
About Author
Written by
Janet White
Janet White has been an esteemed writer and blogger for Difference Wiki. Holding a Master's degree in Science and Medical Journalism from the prestigious Boston University, she has consistently demonstrated her expertise and passion for her field. When she's not immersed in her work, Janet relishes her time exercising, delving into a good book, and cherishing moments with friends and family.
Edited by
Aimie Carlson
Aimie Carlson, holding a master's degree in English literature, is a fervent English language enthusiast. She lends her writing talents to Difference Wiki, a prominent website that specializes in comparisons, offering readers insightful analyses that both captivate and inform.

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