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. It is also one of the important factors in determining the quality of the water.BOD is one of the topics in Biology and they carry a weightage of 3% in NEET and 5% in CBSE and other Paramedical Exams.

What is 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 period. Some of the basic points about biochemical oxygen demand are discussed below:

• Biochemical oxygen demand is one of the important factors which decides water quality and pollution levels in the aquatic environment.

• BOD is normally measured in milligrams of oxygen consumed per liter of water by the standard incubation period which is usually 5 days at 20°C.

• High BOD can also lead to hypoxia where there are low oxygen levels or anoxia where there is no oxygen present. Due to this, there is death of the fish and other aquatic organisms present.

• BOD is also used as a wastewater treatment process as it helps in assessing the effectiveness of the treatment methods that are being used to reduce the organic pollutants such as discharge from hospitals and households.

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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. Some of the major sources are discussed below:

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 litre 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

BOD of Drinking Water

Biochemical oxygen demand is one of the important factors in deciding the quality of the water. It helps in configuring organic pollution levels in the drinking water. Some of the steps are mentioned below which help to decide the safety and suitability of the water for consumption and survival of the aquatic organisms:

• The BOD levels of drinking water can be normally from 1 to 2 ppm. This is considered the safe quality of water for consumption.

• If the value of water ranges from 3 to 5 ppm then it is considered moderately clean water but not very good for consumption.

• While the BOD from 6 to 9 ppm indicates the contaminated water due to organic waste. Water is not suitable for drinking.

• The water which exceeds the value of 100 ppm is considered highly contaminated water with high health risks.

• Although apart from these some organisms like leeches and sludge worms can thrive in low BOD environments due to ecological adaptability.

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.

Factors Influencing Biochemical Oxygen Demand

Several factors influence BOD because it reduces water's dissolved oxygen content and speeds up metabolism. Some of the factors are mentioned below:

1. 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.

2. 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.

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

Types of Questions Asked from Biochemical Oxygen Demand (BOD)

During exam preparation, different types of questions about the Biochemical Oxygen Demand (BOD) are asked. The table below contains the different patterns of questions asked in different exams.

Tips, Tricks, and Strategies for Biochemical Oxygen Demand (BOD)

It takes effort to remember everything in a single go. We made the entire problem easy. Some of the tricks regarding Biochemical Oxygen Demand (BOD) are given below which you can use to memorise the important points.

Understanding BOD

"Q-TRIM: Quality, Treatment, Ratio, Impact, Measurement"

• Q: Quality indicator (BOD measures the organic pollution level in water)

• T: Treatment relevance (used in wastewater treatment to assess organic load)

• R: Ratio of oxygen consumed to organic matter present (indicates level of pollution)

• I: Impact on aquatic life (high BOD leads to reduced dissolved oxygen, harming fish and other organisms)

• M: Measurement method (typically measured in mg/L over a standard incubation period, usually 5 days)

BOD Levels in Water

"C-REPS: Clean, Relative, Elevated, Polluted, Severe"

• C: Clean water (BOD < 3 ppm is considered clean)

• R: Relative cleanliness (3-5 ppm indicates moderately clean water)

• E: Elevated levels (6-9 ppm suggests contamination with organic waste)

• P: Polluted water (BOD > 100 ppm signifies highly contaminated water)

• S: Severe impact (high BOD affects aquatic organisms’ survival due to low dissolved oxygen)

Key Concepts

"M-HEAT: Microorganisms, Hypoxia, Ecosystems, Adaptation, Treatment"

• M: Microorganisms (responsible for consuming oxygen to break down organic matter)

• H: Hypoxia (low oxygen conditions caused by high BOD)

• E: Ecosystems (high BOD can disrupt aquatic ecosystems and food webs)

• A: Adaptation (some organisms can survive in low-oxygen environments)

• T: Treatment methods (monitoring BOD is crucial for effective wastewater treatment)

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