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Question
Which of the following indicates the high BOD in water?
A. Increased DO (dissolved oxygen)
B. Decreased DO (dissolved oxygen)
C. Absence of microbes
D. Presence of microbes
Which of the following indicates the high BOD in water?
A. Increased DO (dissolved oxygen)
B. Decreased DO (dissolved oxygen)
C. Absence of microbes
D. Presence of microbes
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Solution
The correct option is D B and D
The amount of oxygen that would be consumed if all the organic matter in one litre of water were oxidised by bacteria is called as biochemical oxygen demand (BOD).
The amount of biodegradable organic matter in sewage can be indirectly measured by BOD.
The BOD increases when the domestic sewage rich in organic matter is discharged into a water body. This happens due to the presence of microorganisms, which consume a lot of oxygen and breakdown the organic matter. So, there is always a sharp decline in dissolved oxygen when the untreated sewage (rich in organic matter) is discharged as shown in the image. Simultaneously, there is a sharp rise in BOD. Hence statements B and D are correct.
Greater the BOD of waste water, the higher is the amount of organic matter present in it. Higher BOD indicates that more oxygen is utilised for the breakdown of organic matter. It also indicates that this water is not suitable for the survival of aquatic organisms like fishes, as the dissolved oxygen is less. Aquatic organisms like fishes depend on dissolved oxygen for respiration. This causes mortality of fish and other aquatic organisms in this area of sewage discharge.
Further downstream of the sewage flow, the water has been cured of organic matter, so its dissolved oxygen levels return to normal, and BOD also comes back to baseline. This part of the water supports life. Low BOD means less oxygen is being utilised from water, so water is generally cleaner and suitable for aquatic organisms with higher dissolved oxygen levels as shown in the image.
Figure: Effect of sewage discharge on some important characteristics of a water body
The amount of oxygen that would be consumed if all the organic matter in one litre of water were oxidised by bacteria is called as biochemical oxygen demand (BOD).
The amount of biodegradable organic matter in sewage can be indirectly measured by BOD.
The BOD increases when the domestic sewage rich in organic matter is discharged into a water body. This happens due to the presence of microorganisms, which consume a lot of oxygen and breakdown the organic matter. So, there is always a sharp decline in dissolved oxygen when the untreated sewage (rich in organic matter) is discharged as shown in the image. Simultaneously, there is a sharp rise in BOD. Hence statements B and D are correct.
Greater the BOD of waste water, the higher is the amount of organic matter present in it. Higher BOD indicates that more oxygen is utilised for the breakdown of organic matter. It also indicates that this water is not suitable for the survival of aquatic organisms like fishes, as the dissolved oxygen is less. Aquatic organisms like fishes depend on dissolved oxygen for respiration. This causes mortality of fish and other aquatic organisms in this area of sewage discharge.
Further downstream of the sewage flow, the water has been cured of organic matter, so its dissolved oxygen levels return to normal, and BOD also comes back to baseline. This part of the water supports life. Low BOD means less oxygen is being utilised from water, so water is generally cleaner and suitable for aquatic organisms with higher dissolved oxygen levels as shown in the image.
Figure: Effect of sewage discharge on some important characteristics of a water bodySuggest Corrections
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