What is BOD (Biochemical Oxygen Demand) | Civil Engineering Optional Notes for UPSC PDF Download

What is Biochemical Oxygen Demand?

• Biochemical Oxygen Demand (BOD) is the oxygen required by aerobic microorganisms to break down organic matter in water over time.
• Aquatic life depends on dissolved oxygen in water, but when organic matter is present, microbes use this oxygen, reducing what is available for aquatic organisms.
• The more organic matter in water, the higher the BOD, indicating more pollution, often caused by human activities.
• BOD is a crucial measure of water quality, reflecting the impact of organic substances on ecosystems and the appearance of water bodies.

• Water bodies contain dissolved oxygen crucial for aquatic life's respiration.
• Aerobic microbes in the presence of organic matter consume this oxygen, reducing availability for aquatic life.
• Molecular oxygen in water is a byproduct of aquatic plant photosynthesis or atmospheric oxygen in dissolved form.
• Higher Biological Oxygen Demand (BOD) indicates increased pollution in water.
• Increased organic matter often stems from human activities like pollution.
• BOD serves as a key indicator of water quality, reflecting organic content impact on ecosystems and aesthetics.

Measuring Biochemical Oxygen Demand (BOD)

• BOD measurement involves assessing oxygen consumed by bacteria during organic matter decomposition over five days at 20°C.
• Results are expressed in milligrams per liter of water sample.
• Though not highly precise, BOD test is widely used to gauge water pollution potential.
• The BOD test methodology was developed by Sawyer and McCarty in 1978.

Typical Values of BOD and its Indication:

• Below 1 mg/L - Represents pristine water quality.
• 2-8 mg/L - Indicates moderately polluted water.
• Above 8 mg/L - Signifies severely polluted water.

Factors Affecting BOD:

• Temperature
• pH value of the water
• The presence of certain types of microorganisms affecting the growth of aerobic bacteria.
• Type of inorganic substances in water.
• Amount and type of organic substances in water.

In summary, BOD (Biochemical Oxygen Demand) values help determine water quality. Lower values indicate cleaner water, while higher values suggest pollution levels. Various factors like temperature, pH, microorganisms, and organic/inorganic substances influence BOD levels in water.

Type of inorganic substances in water

• Amount and type of organic substance in water.

Significance of BOD:

• Biochemical Oxygen Demand (BOD) is important in various fields:
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  • BOD is crucial in sewage treatment plants, indicating the respiration rate of sewage, sludge, soil, and garbage.
  • It also assesses the respiration rate in living organisms.
  • Measuring BOD helps determine the Chemical Oxygen Demand (COD) of inorganic substances and the pollution level of water.
  • In medical and pharmaceutical industries, BOD is used to gauge the oxygen consumption of cell cultures.

Biochemical Oxygen Demand (BOD)

• Measuring BOD reveals the Chemical Oxygen Demand (COD) of inorganic substances, indicating water's pollution potential.
• BOD is utilized in medical and pharmaceutical sectors to gauge cell cultures' oxygen consumption.

Sources of BOD

Sources increasing the Biological Oxygen Demand in water are natural and man-made. Pollution significantly boosts water bodies' BOD. Regular water usage in a good lifestyle generates substantial wastewater with organic content. Industrial growth intensifies pollution, with factories producing vast amounts of wastewater. Industries such as paper mills, food processing plants, and jute mills are among the major contributors. Environmental factors like surface runoff, debris, dead organisms, and soil erosion also elevate BOD levels. Certain chemicals, like phosphate, elevate drinking water's BOD when present in excess.

Biological Oxygen Demand (BOD) and Sewage Treatment

• Sources increasing BOD of water: natural & man-made, pollution being a major contributor.
• Industries like paper mills, food processing plants, etc., generate significant wastewater.
• Environmental factors contributing to BOD: surface runoff, debris, dead organisms, soil erosion.
• Phosphate is a chemical that raises water's BOD levels significantly.

• BOD is utilized in secondary sewage treatment involving aeration tanks and microbial growth.
• After primary treatment, effluent is treated in aeration tanks with vigorous microbial activity.
• Microbial action reduces organic matter, creating activated sludge.
• Effluent from aeration tanks undergoes settling and further treatment before discharge.

• Microbes in primary effluent consume organic matter.
• Water undergoes treatment until BOD is reduced, becoming activated sludge.
• Effluent from aeration tanks moves to settling tanks for bacterial flocs to settle.
• Further treatment with anaerobic microbes and physicochemical processes follows.
• Final discharge of treated water into water bodies.

Effect of High BOD on Aquatic Ecosystem

• High BOD depletes oxygen in water, harming aquatic life.
• Microbes breaking down waste reduce oxygen crucial for aquatic organisms.
• Results in fish and plant deaths, disrupting the aquatic ecosystem.
• Oxygen levels below 5ppm risk the survival of various aquatic organisms.
• Some freshwater fish species like Catla and rohu cannot survive at such low oxygen levels.
• Deterioration of water body aesthetics and overall beauty.

Pollution and Its Effects on Biochemical Oxygen Demand

• Increasing pollution and urbanization are causing a significant decline in water quality in bodies of water.
• Effective water quality management is crucial for maintaining ecological balance.
• Urbanization results in the generation of large amounts of sewage.
• Insufficient sewage treatment plants lead to the direct discharge of untreated sewage into water bodies.
• This untreated sewage causes severe pollution and raises the Biochemical Oxygen Demand (BOD) levels in water bodies.
• The heightened pollution contributes to the spread of water-borne diseases such as cholera, dysentery, and jaundice.
• The pollution and increased BOD levels have severely affected major rivers like the Ganga and Yamuna in India.
• The Ganga Action Plan (initiated in 1985) and Yamuna Action Plan (started in 1993) by the Ministry of Environment and Forests aimed to save these rivers by constructing more sewage treatment plants to ensure only treated sewage is released into the rivers.

• Increasing BOD and pollution severely affected the Ganga and Yamuna rivers in India.
• The Ganga Action Plan (1985) and the Yamuna Action Plan (1993) were launched by the Ministry of Environment and Forests to rescue these rivers.
• These plans involved constructing numerous sewage treatment plants to ensure only treated sewage entered the rivers.

Methods to Reduce BOD in Water

• Advanced Oxidation Processes (AOP) like H2O2/UV, O3/UV, and Fenton's reagent are effective methods.
• Coagulation with substances such as alum or cationic polymers helps reduce BOD.
• Other methods include flocculation, sedimentation, adsorption with activated charcoal, electro flocculation, UASB, reverse osmosis, and dissolved air floatation.

Coagulation and Water Treatment Methods

• Coagulation using alum or cationic polymers
• Flocculation (e.g. chitosan, isinglass, polyelectrolyte) and sedimentation.
• Adsorption using activated charcoal.
• Electro flocculation.
• Using the up-flow anaerobic sludge blanket reactor(UASB).
• Reverse osmosis.
• Dissolved air floatation technique.

Water is essential for all life on Earth. It is crucial that we conserve and protect water resources to prevent pollution. Pollution of water bodies has a direct negative impact on all living organisms, including humans. Increasing levels of biochemical oxygen demand (BOD) in water ecosystems harm the overall ecological balance of our planet. It is our responsibility to preserve these ecosystems and maintain a healthy environment for all forms of life. We need to prioritize the reduction of BOD levels and actively work towards the conservation of water bodies.

Water Conservation and Biochemical Oxygen Demand

• Water is essential for all life on Earth.
• We must conserve water and prevent pollution to protect all living beings.
• Pollution harms ecosystems and biodiversity.
• Biochemical Oxygen Demand (BOD) is the measure of oxygen consumed by microorganisms in water while breaking down organic matter.

Affecting Factors of Biochemical Oxygen Demand

• Factors influencing BOD include:
• Various affecting factors impact biological chemical demand.