Biological Oxygen Demand (BOD)
BOD is an important factor in determining the quality of water since it determines the quantity of oxygen required by microorganisms to break down the organic matter in water. BOD is used in the management and treatment of wastewater and it is an indicator of the level of organic pollution in water bodies.
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Importance of BOD
- Water Quality Assessment: BOD stands for biological oxygen demand, which is a measure of the amount of organic pollution in water that is useful in assessing water quality.
- Environmental Impact: High BOD levels can cause oxygen depletion in water bodies and hence have a negative impact on aquatic life.
- Treatment Efficiency: The BOD levels should be closely monitored in order to determine the efficiency of the wastewater treatment processes.
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Measurement of BOD
- Principle: BOD is calculated by estimating the amount of dissolved oxygen (DO) used by the microorganisms in breaking down the organic matter in a water sample within a given time, which is five days (BOD₅).
- Procedure:
- Sample Collection: Take water samples in BOD bottles and make sure that there are no air bubbles in the bottles.
- Initial DO Measurement: Determine the initial DO concentration using a DO meter.
- Incubation: Place the sample in the dark at 20°C to avoid photosynthesis which may alter the DO levels in the water.
- Final DO Measurement: At the end of the incubation period, determine the final DO concentration.
- Calculation: BOD is determined by the difference in DO concentration before and after the incubation period.
- Units: BOD is measured in milligrams per liter (mg/L) of dissolved oxygen used up by the organisms.
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Factors Affecting BOD
- Organic Matter: The BOD is affected by the concentration and type of organic pollutants in the water sample.
- Microbial Population: The presence and activity of microorganisms that decompose organic matter have an influence on BOD values.
- Temperature: Higher temperatures can also enhance microbial growth and hence lead to higher BOD values.
- Inhibitory Substances: The use of chemicals that suppress microbial growth can lead to low BOD values.
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Applications of BOD
- Wastewater Treatment: BOD is used to assess and regulate the effectiveness of biological treatment processes in water treatment facilities.
- Environmental Monitoring: BOD is used by regulatory agencies to determine the effect of effluent discharge on natural water bodies.
- Pollution Control: BOD levels are closely watched by industries to meet the discharge permits and other environmental standards.
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BOD vs. COD
- Chemical Oxygen Demand (COD): COD determines the quantity of oxygen that is needed to oxidise both organic and inorganic compounds present in water.
- Differences:
- Method: BOD is based on the degree of biological oxidation, while COD employs a powerful chemical oxidizing agent.
- Time Frame: BOD normally requires 5 days (BOD5) to be determined while COD can be determined within a few hours.
- Scope: BOD is mainly used to estimate biodegradable organic pollution while COD encompasses both biodegradable and non biodegradable substances.
Conclusion
BOD is one of the most important parameters that are used to determine the quality of water and also to control the treatment of wastewater. BOD is useful in determining the oxygen demand of the organic matter in water and hence the pollution load and the likely effects on the environment. The monitoring of BOD is important in checking compliance with set regulatory requirements and aids in water quality management.