Question

Biochemical Oxygen Demand, (BOD) is a measure of organic material present in water. BOD value less than 5 ppm indicates a water sample to be (A) rich in dissolved oxygen (B) poor in dissolved oxygen (C) highly polluted (D) not suitable for aquatic life

Short answer

A BOD value less than 5 ppm indicates that the water sample is \( \textbf{(A) rich in dissolved oxygen} \).

Step-by-step solution

Understand Biochemical Oxygen Demand (BOD)

Biochemical Oxygen Demand (BOD) is the amount of dissolved oxygen required by aerobic microorganisms to break down the organic matter in a water sample. A high BOD value indicates that there is a lot of organic material present in the water, requiring more oxygen for decomposition. This leads to reduced oxygen levels in the water. Conversely, a low BOD value signifies that there is less organic material present, meaning the water has a higher dissolved oxygen content. Now, let's analyze each of the given options related to BOD values.

Option A: Rich in dissolved oxygen

If the BOD value is less than 5 ppm, it means there is less organic material present in the water. Consequently, there is a smaller demand for oxygen by the microorganisms, so the water will likely be rich in dissolved oxygen.

Option B: Poor in dissolved oxygen

This option contradicts the fact that a low BOD value means less demand for oxygen by the microorganisms present. If the BOD value is less than 5 ppm, it cannot be poor in dissolved oxygen.

Option C: Highly polluted

A low BOD value indicates less organic material present, which means the water is not highly polluted. This option is incorrect.

Option D: Not suitable for aquatic life

Aquatic life generally thrives in water that is rich in dissolved oxygen. Since a low BOD value (<5 ppm) indicates higher dissolved oxygen content, it means the water is suitable for supporting aquatic life. Thus, this option is incorrect.

Conclusion

Based on the analysis, a BOD value less than 5 ppm indicates that the water sample is (A) rich in dissolved oxygen.

Key concepts

Dissolved Oxygen

Dissolved oxygen is a crucial element in aquatic ecosystems. It refers to the amount of gaseous oxygen that is mixed within the water. Aquatic animals, such as fish, rely on dissolved oxygen for survival. The right level of dissolved oxygen is essential for the health of these ecosystems.

When dissolved oxygen is abundant, aquatic life flourishes as it ensures adequate respiration for fish and other aquatic organisms. Conversely, low levels of dissolved oxygen, which can occur when there is an excess of organic material, may lead to stress and, in extreme cases, the death of aquatic organisms. This highlights the importance of measuring and maintaining healthy levels of dissolved oxygen to sustain aquatic life.

Organic Material in Water

Organic material in water consists largely of decomposing plant and animal matter. It also includes waste products from various sources, such as sewage and run-offs from agriculture. When organic materials enter water bodies, they serve as food for aerobic microorganisms.

These microorganisms break down the organic matter through a process that consumes dissolved oxygen. A large amount of organic material increases the demand for oxygen, leading to a high biochemical oxygen demand (BOD). This is because more microorganisms are present, requiring more oxygen to decompose the added organic material.

Effectively managing the levels of organic material ensures that the demand for oxygen remains balanced, thereby maintaining healthy aquatic environments.

Aquatic Life Suitability

Aquatic life suitability refers to the ability of a water body to support different forms of aquatic organisms. The presence of adequate dissolved oxygen is a key factor in determining this suitability.

When the dissolved oxygen levels are high and the BOD is low, it typically indicates a water environment that is conducive to aquatic life. Species such as fish, crustaceans, and aquatic plants need sufficient oxygen levels to thrive.

A low BOD, such as less than 5 ppm, often signals water that is rich in oxygen, making it suitable for healthy aquatic ecosystems. Maintaining these conditions is crucial to preserving biodiversity and supporting robust populations of aquatic organisms.