Question

As the organic matter increases in a water body, the BOD
a) Increases
b) Decreases
c) Remains unchanged
d) Not a parameter

Answer 1

Biological Oxygen Demand(BOD) is a measure of the amount of dissolved oxygen needed by anaerobic biological organisms to remove waste organic matter from water. BOD measurements generally indicate the pollutant organic materials in the water.

Complete step by step answer:
- The common lake or stream contains a small amount of oxygen in the form of dissolved oxygen. Dissolved oxygen is an important component of natural water bodies maintaining aquatic life.
- Environmental stresses and other human- induced factors can lessen the amount of dissolved oxygen in the water.
- Sources of BOD include leaves and Woody debris, animal manure, effluents from pulp and paper mills, food processing plants, etc.
- When this organic matter pollutes the water BOD demand increases as water contains a large number of organisms which involves the biodegradation of organic matter.
- Greater the biological oxygen demand, the lower the amount of dissolved oxygen available for higher animals such as fishes.
So, the correct answer is, "Increasing".

Additional information:
- In the treatment of wastewater plants the Biological oxygen demand is used that shows the index of the degree of organic pollution in the water.
- Rivers with quite less or no pollutants tends to have a BOD level below 1 mg/liter
- Moderately polluted rivers may have BOD value in the range of 2 to 8 mg/liter.
- Heavily polluted rivers have a BOD value exceeding 8 mg/liter.

Note: In order to maintain a low BOD level, there are mandates and all the industries must process their waste through treatment procedures before disposing of the water into the lakes, rivers, or oceans.
- Coldwater withhold oxygen better than warm water thus dissolved oxygen levels are low in summer months.