What is BOD? Meaning, Importance, and Measurement in Wastewater

In industrial processes, agriculture, and daily human life, water is used and wastewater is generated. Assessing wastewater quality is necessary to prevent environmental impacts. One of the most commonly used standard values is BOD, which stands for Biochemical Oxygen Demand, reflecting the oxygen demand of microorganisms to decompose organic matter in water. Knowing and understanding the BOD value helps us control water quality more effectively.

What is BOD?

BOD stands for Biochemical Oxygen Demand. It is used to indicate the amount of oxygen that microorganisms require to decompose organic matter in wastewater over a specific period. The standard measurement method is called BOD, which refers to a 5-day test at a temperature of 20°C.

A high BOD value in water means there is a large amount of organic matter waiting to be decomposed, causing microorganisms to consume more oxygen. If the oxygen is insufficient, the water becomes a source of pollution, affecting aquatic animals, plants, and the surrounding ecosystem.

Why Measure BOD?

Measuring BOD is not just for academic water quality assessment; it is also a mandatory criterion used by many government agencies, such as the Pollution Control Department or the World Health Organization, to set industrial effluent standards.

The main reasons to measure BOD include:

To control the quality of effluent from industrial plants to ensure it does not exceed legally defined standards.
To evaluate the efficiency of wastewater treatment systems; if the system works well, the post-treatment BOD value will be low.
To reduce environmental impact by preventing wastewater from flowing into rivers, canals, or the sea, which can cause aquatic life to die.
To serve as a comparative index between different water sources to rank the severity of pollution.

How to Measure BOD

There are several methods for measuring BOD, but the most popular is BOD, which takes 5 days. The main procedure involves incubating a water sample in a bottle with a known amount of dissolved oxygen and then measuring it again after 5 days to see how much oxygen the microorganisms have consumed.

Additionally, there are short-term BOD tests or automated measuring instruments for faster results, but BOD generally remains the international standard.

Key points for BOD measurement:

Wastewater samples must be collected properly to avoid contamination.
Samples should be stored at low temperatures to halt microbial activity before testing.
Results must be compared with the standards set by government agencies.

The Difference Between BOD, COD, and DO

Many people might confuse BOD, COD, and DO, which are all related to water quality assessment.

BOD (Biochemical Oxygen Demand): The oxygen demand of microorganisms to decompose organic matter.
COD (Chemical Oxygen Demand): The oxygen demand to oxidize organic matter using chemicals.
DO (Dissolved Oxygen): The amount of oxygen dissolved in water.

Generally, the COD value is higher than the BOD value because chemicals can oxidize both biodegradable and non-biodegradable organic matter. The DO value indicates whether there is enough oxygen in the water for living organisms.

BOD and the Environment

When a water source has a high BOD, it causes aquatic animals to die from lack of oxygen, leading to polluted water and foul odors. This affects both the ecosystem and the communities surrounding the water source.

Potential impacts if BOD exceeds standards:

Polluted water and unpleasant odors.
Mass death of aquatic animals.
Abnormal growth of aquatic plants.
Deterioration of the aquatic ecosystem.
Negative health impacts on surrounding communities.

How to Control BOD in Wastewater

To reduce BOD before discharging wastewater into the environment, factories and businesses often use wastewater treatment systems, such as:

Physical treatment like filtering and sedimentation to reduce solids in wastewater.
Biological treatment like Activated Sludge or Aerated Lagoons, which use microorganisms to decompose organic matter.
Chemical treatment, such as adding chemicals to accelerate decomposition.

Furthermore, regular monitoring is essential to ensure that the post-treatment BOD value remains within the standard limits.

Conclusion

In summary, BOD is a crucial index for assessing water quality, especially industrial wastewater. Understanding its principles, measurement methods, and the impacts of exceeding standard BOD levels allows us to plan wastewater treatment appropriately, reduce environmental impact, and protect the quality of life in society.