Biochemical Oxygen Demand: Overview, Sources, Principle, Procedure, Measurement Methods

BOD (Biochemical oxygen demand) is defined as the quantity of dissolved oxygen required by aerobic biological organisms in a body of water, at a particular temperature, for a specific amount of time, in order to decompose the organic material present in a water sample.

When you look at the water in a lake, oxygen is one thing you cannot see. We tend to think of water as the antithesis of air, but the typical lake or stream does contain trace amounts of dissolved oxygen. The presence of a sufficient concentration of dissolved oxygen is crucial to maintaining the health of natural water bodies, even though the amount of dissolved oxygen is small.

How much oxygen is needed to decompose organic matter in water is generally described by the term "biochemical oxygen demand" (BOD).

Biochemical Oxygen Demand

The biochemical oxygen demand (BOD), also known as biological oxygen demand (BOD), is the quantity of oxygen required or demanded by aerobic microorganisms to decompose the organic matter present in a specific water sample at a particular temperature and over a specific time period.

For its respiratory needs, aquatic life depends on the dissolved oxygen that is present in water bodies. Aerobic microbes use the dissolved oxygen in the water to break down organic matter when it is present in a water body. This decreases the amount of oxygen that is available for aquatic life. Water contains molecular oxygen that is either a byproduct of photosynthesis carried out by aquatic plants or atmospheric oxygen that has been dissolved.

A water body's or water sample's pollution level increases with its BOD. However, anthropogenic causes like pollution account for the majority of the increase in organic matter. For gauging the quality of water, BOD is used as an index. As part of managing water quality, it is crucial to identify the amount of organic matter in a body of water and how it affects the ecosystem and aesthetics of the water body.

Biochemical Oxygen demand (BOD) Sources

Sources that raise biological oxygen levels are both natural and man-made demands for water. The BOD of water bodies is largely influenced by pollution. A healthy lifestyle is characterized by regular, ample water use that produces large amounts of wastewater with organic content. Pollution is multiplying as industrialization increases.

Large amounts of wastewater are produced in factories. Paper mills, food processing facilities, jute mills, etc. are a few examples of industries with significant wastewater production. Floating debris, dead plants and animals, soil erosion, surface runoff, and other environmental factors all contribute to an increase in BOD. Few chemicals have an impact on drinking water's BOD.

Sources of biological oxygen demand include leaves and other organic matter, dead plants and animals, animal manure, effluents from pulp and paper mills, wastewater treatment facilities, feedlots, food-processing facilities, failing septic systems, and urban stormwater runoff.

Particularly recently, phosphate pollution from American households has been one of the most significant nutrients affecting BOD in aquatic systems.

BOD of Drinking Water

BOD levels in drinking water range from 1 to 2 ppm. Water is deemed to be moderately clean when its BOD value is between 3 and 5 ppm. BOD levels in contaminated water are between 6 and 9 ppm. Some organic waste can be found in contaminated water. Bacteria break down this organic material. A BOD value of more than 100 ppm denotes highly contaminated water. BOD levels in pure water should be less than 5 ppm.

Because there is less dissolved oxygen (DO) when BOD is high, organisms that require high DO cannot survive. These organisms include mayfly nymphs and caddisfly larvae. However, some organisms, like leeches and sludge worms, can survive with less DO.

Significance of BOD

The importance of biochemical oxygen demand is found in many different fields.

• These are - sewage treatment plants are where BOD is most important. It provides information on how quickly soil, sewage, sludge, and garbage breathe.

• The Chemical Oxygen Demand, or COD, of inorganic substances is determined by measuring BOD.

• It shows that water has the potential to pollute.

• BOD is used in the healthcare and pharmaceutical sectors to gauge how much oxygen cell cultures are consumed.

• BOD is a measurement of how much oxygen is used by microorganisms in the process of decomposing organic matter in water bodies.

• It shows how much organic pollution there is in an aquatic ecosystem.

• To determine how effectively aerobic microbes are destroying organic wastes, BOD is calculated during sewage treatment or wastewater treatment.

• In living things, the rate of respiration is also governed by the biochemical oxygen demand.

Factors influencing Biochemical Oxygen Demand

Temperature influences BOD because it reduces water's dissolved oxygen content and speeds up metabolism.

pH: An irregular pH value causes a noticeable decrease in the rate at which organic compounds are removed, which has a big impact on BOD measurements.

Organic substances present in water: Water's biochemical oxygen demand is influenced by the types and concentrations of organic substances, which determine the rate of dissolved oxygen consumption.

Microorganism Types: A number of microorganisms promote the growth of aerobic bacteria, which in turn affect BOD.

How is BOD calculated?

After five days of incubation at a temperature of 20 degrees Celsius, BOD is calculated and expressed as milligrams of oxygen consumed per liter of sample. BOD is calculated using the formula BOD = [D(i) - D(f)]/P.

Where:

D(i) = Initial concentration of dissolved oxygen

D(f) = Dissolved oxygen concentration for the last five days

P = Wastewater Volumetric Fraction