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Difficulty: EasyPollution Types, Causes, Effects, and Control

Which of the following environmental changes occurs in a freshwater river immediately following the discharge of untreated domestic sewage?

  1. A sharp increase in the Biological Oxygen Demand (BOD)Answer
  2. B
    A significant increase in dissolved oxygen concentration
  3. C
    A rapid decline in the population of saprophytic bacteria
  4. D
    A complete removal of nitrate and phosphate ions from the water

Answer

A sharp increase in the Biological Oxygen Demand (BOD)
Discharging untreated domestic sewage introduces large quantities of biodegradable organic matter into aquatic environments. Aerobic decomposers utilize this organic load as a food source, leading to intensive aerobic respiration. This rapid consumption of oxygen elevates the Biological Oxygen Demand (BOD) of the water body.

Step-by-Step Solution

1
Identify the primary components introduced by untreated domestic sewage into aquatic ecosystems.
Untreated domestic sewage contains high amounts of organic waste materials and nutrients.
Understanding the pollutant composition helps determine the immediate biological response in the water body.
2
Analyze the biological response of aerobic decomposers to organic waste.
Saprophytic bacteria feed on organic waste and reproduce rapidly, consuming dissolved oxygen during aerobic respiration.
Increased bacterial activity requires more oxygen, which is measured as Biological Oxygen Demand (BOD).
3
Select the option describing the correct environmental effect.
The discharge causes a sharp increase in the Biological Oxygen Demand (BOD).
High organic loading directly correlates with high BOD values.

Key Concept

Biological Oxygen Demand (BOD) and Sewage Pollution
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Topics

Pollution Types, Causes, Effects, and Control

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