Difference Between Biochemical Oxygen Demand (BOD) and Chemical Oxygen Demand(COD)

The difference between BOD and COD is that BOD measures the quantity of oxygen consumed by aerobic microorganisms to break down organic matter in water whereas COD measures the amount of oxygen needed to chemically oxidize all organic and inorganic contaminants in water without the aid of microbes. A potent oxidizing agent is needed for COD. Unlike BOD, it completely oxidizes contaminants into CO₂ and H₂O. Furthermore, BOD tests take longer to complete than COD testing, which can be finished in a few hours. This article provides detailed information on the differences between BOD and COD.

Difference Between BOD and COD

The table below lists all the major differences between BOD and COD:

Features	BOD	COD
Definition	It estimates the quantity of oxygen needed by the aerobic microbes to breakdown organic matter.	It estimates the oxygen needed to breakdown organic as well as inorganic constituents present in the wastewater by chemical reaction.
Decomposition	It is a biological oxidation process.	It is a chemical oxidation process.
Agents	It is performed by aerobic organisms.	It is performed by chemical reagents.
Time Taken for Determination	BOD value is determined in 5 days.	COD is estimated within few days.
Values of Measurement	BOD value is lesser than COD always.	COD value is always greater than BOD which means that more organic material can be oxidized through the COD test.
Test Procedure	BOD is measured by keeping a sealed water sample for incubation for a period of 5 days at 20°C. The difference in the amount of dissolved oxygen tells us the quantity of oxygen used by the aerobic microbes.	For COD test, the water sample is subjected to incubation with boiling sulfuric acid and a potent oxidant for a specific amount of time and temperature.
Permissible Limit of Test	The permissible limit is 30 mg/L for BOD test.	The permissible limit is 250-500 ppm for COD test.
Oxidation Ability	Organic waste and naturally occurring organic residues in water can be oxidized by biological oxidation.	Industrial sewage is only degraded by COD. But, it is noteworthy to mention that COD does not measure the oxygen consumption of acetate.
Analysis	BOD analysis is slower and less accurate than COD analysis.	COD analysis is far more accurate and faster than BOD .

Full form of BOD and COD

The full form of BOD and COD is Biochemical Oxygen Demand and Chemical Oxygen Demand respectively. BOD and COD are the two main primary parameters of water quality and the level of organic pollution or contamination. They also demonstrate how strongly sewage and wastewater need oxygen in the water. BOD and COD are used to measure the oxygen demand of wastewater during the treatment process in a sewage treatment facility.

What is Biochemical Oxygen Demand (BOD)?

The quantity of dissolved oxygen required by aerobic bacteria to break down organic compounds in sewage water. BOD is a biological process rather than a simple test. BOD testing, however, is a frequently employed method to assess the quality of water. This test measures BOD by measuring the quantity of oxygen lost during a five-day incubation period for a sealed water sample.

Common sources of BOD include animal dung, woody debris, topsoil, leaves, food processing facilities, wastewater treatment facilities, urban stormwater runoff, and the effluents of pulp and paper mills. The overall rate of oxygen consumed by microorganisms depends on the prevailing pH and temperature. With rising BOD levels, aquatic life forms in a given water body have less access to oxygen. Aquatic life forms would be more stressed, suffocate and ultimately perish due to high BOD.

What is Chemical Oxygen Demand (COD)?

Chemical oxygen demand (COD) is the amount of oxygen needed for the chemical oxidation of organic and inorganic compounds in wastewater by oxidizing agents such as potassium dichromate and potassium permanganate. Chemical Oxygen Demand is almost identical to Biochemical Oxygen Demand in that they are both used to calculate the oxygen demand of a wastewater sample. The difference between the two is that Biochemical Oxygen Demand only measures the oxygen demanded by organisms whereas Chemical Oxygen Demand measures everything that can be oxidized.

Chemical Oxygen Demand analysis is usually conducted when a strong oxidizing chemical is utilized. When a potent oxidizing agent is utilized, chemical oxygen demand analysis is usually carried out. For instance, organic matter oxidizes to give water and carbon dioxide in acidic environments. The amount of oxidizing chemical consumed throughout the test is used to compute the amount of organic matter or the oxygen demand.

FAQ’s – BOD and COD

1. Why COD is better than BOD?

Wastewater that is too hazardous for the BOD test can be tested using COD. Rather than serving as a BOD test substitution, the COD test must to be considered an independent assessment of the organic matter in a wastewater sample.

2. What is BOD vs COD vs TOC?

The conventional methods that are frequently used are Biological Oxygen Demand (BOD) and Chemical Oxygen Demand (COD). The oxygen-depleting effects of waste pollutants are measured by BOD and COD. Total Organic Carbon (TOC) measurement, which measures both organic and inorganic carbon directly, is the one exception to this rule.

3. What is the Difference between COD and BOD?

COD is the total amount of oxygen needed for chemical oxidation to break down organic materials. In contrast, BOD is the amount of oxygen needed by the microorganisms to break down organic matter in an aerobic environment.

4. Which is Faster BOD or COD?

The COD test is faster than the BOD test, which usually takes five days, and is not affected by harmful compounds. It just takes three hours. You must use potassium hydrogen phthalate (KHP) to prepare a number of standards before completing the COD test.

5. Why COD is Higher than BOD in Wastewater?

Since more organic chemicals can be chemically oxidized than biologically oxidized, COD is often higher than BOD. This includes substances that are harmful to living things, which is why COD tests are beneficial for analyzing industrial waste because BOD testing is unable to detect them.