BOD and COD Full Form
What is the full form of BOD and COD?
(BOD) "Biological Oxygen Demand," and (COD) "Chemical Oxygen Demand" are the two most important parameters to characterize or measure the degree of pollution of waste water.
BOD is the biological demand for oxygen, a source of water and is the amount of oxygen used by microorganisms to break down organic substances. These are usually aerobic or anaerobic bacteria, yeasts and plankton present in the water. It is the degree of contamination in water and is expressed in mgO2/L. It is measured by a time-consuming biological process, which depends only on temperature. This measurement is performed at 20°C for 5 days and is called BOD5.
COD is the chemical demand for oxygen by a source of water, which is the amount of oxygen required to break down the organic substances chemically and convert them into CO2 and H2O. It is expressed in mgO2/L, and the higher the COD measure, the more polluted the water is. This test takes about 3 hours. Therefore, much less time is needed for a result as compared to a BOD test.
Biochemical Oxygen Demand
Biochemical Oxygen Demand (BOD) is the amount of oxygen used by bacteria and microorganisms when they decompose organic matter under aerobic conditions.
The lakes or streams might contain small amounts of oxygen in the form of (DO) dissolved oxygen. Dissolved oxygen is an important component of natural water bodies, which helps in maintaining the aquatic life and quality of the streams and lakes. Some human-induced factors can lessen the amount of dissolved oxygen in a water body.
The BOD test can be used as an indication of the measure of oxygen consumption. It is commonly expressed in the form of milligrams of oxygen consumed per liter of sample in 5 days (BOD5) of incubation at 20°C.
Biological oxygen demand affects the amount of dissolved oxygen in water bodies like rivers and streams. The rate of oxygen consumption depends on a number of variables like temperature, the presence of certain kinds of microorganisms, pH and the type of organic and inorganic material present in the water body.
Chemical Oxygen Demand
The amount of oxygen used by the reactions in a measured solution is indicated by the COD or chemical oxygen demand. It is expressed in the form of oxygen consumed over the volume of the solution, in other words, milligrams per litre (mg/L), in SI units. Chemical Oxygen Demand is helpful for measuring the quality of water.
Chemical oxygen demand (COD) is the amount of oxygen required for the chemical oxidation of organic and inorganic substances found in water using oxidizing agents such as potassium permanganate, potassium dichromate, etc.
The sample water is taken in a sealed container and exposed to an oxidant such as potassium dichromate and sulfuric acid for a known amount of time and temperature to measure COD. The COD test will calculate the oxygen concentration needed to oxidize the organic molecules present in water chemically.
Difference between BOD and COD
The fundamental difference between BOD and COD is that BOD is the quantity of oxygen used by the bacteria during the aerobic decomposition of organic matter, on the other hand, COD refers to the amount of oxygen required for the chemical oxidation of the total organic matter present in water.
The COD analysis is comparatively faster and more precise. When wastewater including bacteria and organic impurities is dumped into a stream or lake, a BOD test is performed to determine the effect it will have on animal and plant life. In order to break down the organic materials in the water, bacteria will require oxygen.
On the other hand, COD analysis is a measurement of the capability of an organic wastewater sample's oxygen depletion. It calculates the amount of equivalent quantity of oxygen required to chemically oxidize organic molecules in water and to remove pollution.
Frequently Asked Questions (FAQs)
By adding hydrogen peroxide into the wastewater solution, BOD and COD can be reduced. The wastewater's organics will be attacked by hydrogen peroxide, which will degrade and lower the measured BOD and COD.
COD is usually higher than BOD because chemical oxidation is comparatively easier than biological oxidation.
While measuring the oxygen demand, the carbonaceous stage is taken into consideration. This stage is completed in 5 days, which means that the organic content of the sewage is oxidized in aerobic conditions in 5 days. Therefore, BOD for five days is calculated.
Sources of BOD include leaves and woody debris; dead animals and plants; animal manure, wastewater treatment plants, failing septic systems and urban water runoff.
The oxygen consumed by aquatic organisms for respiration and metabolism is significantly reduced by the microorganisms for breaking down organic waste which results in the death of aquatic plants and fishes and leads to complete disruption in the aquatic ecosystem.