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

Edited by Tayyaba Rehman — By Fiza Rafique — Published on January 16, 2024
Biochemical Oxygen Demand (BOD) measures organic matter degradation by microorganisms; Chemical Oxygen Demand (COD) measures total chemically oxidizable pollutants.
Biochemical Oxygen Demand vs. Chemical Oxygen Demand — What's the Difference?

Difference Between Biochemical Oxygen Demand and Chemical Oxygen Demand


Key Differences

Biochemical Oxygen Demand (BOD) is a measure of the amount of oxygen that microorganisms will consume while decomposing organic matter in water. Over a standard period, typically five days at 20°C, the depletion of oxygen indicates the biodegradable organic matter's level, reflecting the pollutant load in wastewater.
Chemical Oxygen Demand (COD), on the other hand, is a measure of all chemicals (organic and inorganic) in the water that can be oxidized. It is determined through a chemical process involving a strong chemical oxidant, usually dichromate in acidic conditions, to fully oxidize the sample and measure the oxygen equivalent of the organic matter present. The process does not differentiate between biologically active and inert organic matter.
In water quality testing, BOD is often used to gauge the effectiveness of wastewater treatment processes. A lower BOD value after treatment indicates a reduction in waste organic material and a lesser impact on the aquatic ecosystem if the water is released. BOD specifically provides insight into the potential for oxygen depletion in receiving waters.
Chemical Oxygen Demand is more inclusive than BOD, encompassing not just biodegradable organics but also compounds that biological processes cannot readily break down. COD is a faster test than BOD, requiring only a few hours compared to several days. COD is used to measure the short-term impact of a discharge on the oxygen levels of receiving waters.
Both BOD and COD are critical parameters for environmental monitoring and wastewater management. While BOD offers a biological perspective on water quality, focusing on organic pollution that affects aquatic life, COD offers a broader chemical perspective, which is important for overall water treatment and pollution control strategies.

Comparison Chart


Oxygen needed for microbial decomposition.
Oxygen equivalent of oxidizable matter.

Measure of

Organic matter biodegradability.
Total potential to consume oxygen.

Testing Method

Biological process over days.
Chemical process in hours.

Types of Pollutants

Primarily organic biodegradable pollutants.
Organic and inorganic oxidizable pollutants.


Water treatment efficiency, ecological impact.
Pollution control, treatment efficiency.

Compare with Definitions

Biochemical Oxygen Demand

BOD indicates the amount of oxygen required by bacteria to decompose organic matter in water.
The river's high BOD suggests significant contamination from organic waste.

Chemical Oxygen Demand

COD tests are a quick method for evaluating water's oxygen demand.
Emergency testing for COD helped assess the spill's impact on the river.

Biochemical Oxygen Demand

BOD measurement reflects the potential for oxygen depletion in water bodies.
Concern for fish kills is warranted when BOD values are elevated.

Chemical Oxygen Demand

COD is a broader measure of water quality compared to BOD.
While BOD focuses on biodegradation, COD encompasses the total oxidizable matter.

Biochemical Oxygen Demand

It represents the oxygen level needed to break down organic materials aerobically.
The wastewater treatment plant aims to reduce BOD before discharge.

Chemical Oxygen Demand

COD measures the total quantity of oxygen needed to chemically oxidize organic and inorganic substances in water.
The factory's effluent showed a high COD, indicating a heavy load of pollutants.

Biochemical Oxygen Demand

It is a gauge of water quality and the level of organic pollution.
A rising BOD level could signal an increase in pollutants entering the ecosystem.

Chemical Oxygen Demand

It is a critical parameter for assessing the amount of pollution in wastewater.
Regulators use COD to determine if industrial discharge meets water quality standards.

Biochemical Oxygen Demand

BOD testing involves measuring dissolved oxygen consumption over a set period.
Their BOD test indicated a low impact from the new eco-friendly detergent.

Chemical Oxygen Demand

It involves the use of strong oxidizing agents to digest pollutants.
COD levels are assessed to monitor the effectiveness of advanced oxidation processes.

Common Curiosities

Why is BOD important?

It helps assess the impact of wastewater on aquatic life.

What does COD stand for?

Chemical Oxygen Demand.

Why is COD important?

It provides a quick measure of overall oxidizable pollutants in water.

How is BOD measured?

By assessing the oxygen depletion over five days.

What does a high COD indicate?

High levels of total oxidizable pollutants.

Is COD a measure of pollution?

Yes, for both organic and inorganic pollution.

What does BOD stand for?

Biochemical Oxygen Demand.

How is COD measured?

Through a chemical reaction, typically completed in a few hours.

What does a high BOD indicate?

High levels of biodegradable organic waste in water.

What affects BOD levels?

The amount of organic matter and microbial activity.

Is BOD a measure of pollution?

Yes, particularly for organic pollution.

Can BOD or COD predict the oxygen levels in natural waters?

Yes, both can give an indication of potential oxygen depletion.

Can BOD and COD values be the same?

Rarely, as COD generally measures a broader spectrum of substances.

What affects COD levels?

The concentration of all oxidizable compounds, organic or inorganic.

Are BOD and COD used together?

Yes, for a comprehensive assessment of water quality.

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Author Spotlight

Written by
Fiza Rafique
Fiza Rafique is a skilled content writer at, where she meticulously refines and enhances written pieces. Drawing from her vast editorial expertise, Fiza ensures clarity, accuracy, and precision in every article. Passionate about language, she continually seeks to elevate the quality of content for readers worldwide.
Tayyaba Rehman is a distinguished writer, currently serving as a primary contributor to As a researcher in semantics and etymology, Tayyaba's passion for the complexity of languages and their distinctions has found a perfect home on the platform. Tayyaba delves into the intricacies of language, distinguishing between commonly confused words and phrases, thereby providing clarity for readers worldwide.

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