UPSC Prelims 2017 Question:

Biological Oxygen Demand (BOD) is a standard criterion for

Explanation: 

• Biological Oxygen Demand (BOD) is defined as the amount of dissolved oxygen needed by aerobic biological organisms in a body of water to break down the organic material present in a water sample, at a specific temperature and specified period.
  
  
• Determining how organic matter affects the concentration of dissolved oxygen in a stream or lake is integral to water-quality management. BOD is a measure of the amount of oxygen required to remove waste organic matter from water in the process of decomposition by aerobic bacteria (those bacteria that live only in an environment containing oxygen). The waste organic matter is stabilized or made unobjectionable through its decomposition by living bacterial organisms which need oxygen to do their work. BOD is used, often in wastewater-treatment plants, as an index of the degree of organic pollution in water.
  
  

Therefore, option (3) is the correct answer.

Subject: Environment | Pollution