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Difficulty: MediumWater Pollution, Industrial Effluents, and Water Treatment

A river downstream from a processing factory exhibits a high Biochemical Oxygen Demand (BOD) reading following the discharge of organic effluent. Which process directly accounts for the depletion of dissolved oxygen in this aquatic environment?

  1. Aerobic micro-organisms consuming dissolved oxygen while breaking down the organic wasteAnswer
  2. B
    Rapid microbial degradation of non-biodegradable synthetic addition polymers present in the water
  3. C
    Thermal decomposition of hydrogen trioxocarbonate(IV) during the removal of temporary hardness
  4. D
    Depletion of oxygen gas in water caused directly by chlorofluorocarbon destruction of the atmospheric ozone layer

Answer

Aerobic micro-organisms consuming dissolved oxygen while breaking down the organic waste
When organic effluent enters a water body, aerobic micro-organisms proliferate and decompose the organic matter via oxidation. This process consumes large amounts of dissolved oxygen, resulting in a high Biochemical Oxygen Demand (BOD) and reduced dissolved oxygen levels in the aquatic habitat.

Step-by-Step Solution

1
Identify the source of pollution
The factory effluent supplies large amounts of organic material to the water body.
Organic waste acts as a nutrient substrate for aerobic bacteria.
2
Analyze the biochemical process of organic waste breakdown
Aerobic bacteria oxidize the organic compounds into simpler inorganic molecules, using up dissolved oxygen in the process.
Biochemical Oxygen Demand (BOD) measures the quantity of oxygen needed by aerobic organisms to break down organic matter.
3
Relate BOD to dissolved oxygen levels
A high BOD value indicates intensive microbial respiration, leading directly to oxygen depletion in the river.
Oxygen consumption by micro-organisms exceeds the re-aeration rate of the water.

Key Concept

Biochemical Oxygen Demand (BOD) and Organic Water Pollution
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Topics

Water Pollution, Industrial Effluents, and Water Treatment

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