Question

Which of the following retards in self-purification of stream
PRN: 2018015201014033, NOTE: SCREENSHOT PROHIBITED
А
higher temperature
B
sunlight
fulfill the oxygen demand
D
None of the above
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Answer 1

Answer:

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Answer 2

D. None of the above

Self-purification of streams: The ability of streams to purify itself naturally and to bring back the polluted water into its original purified condition is called self-purification of streams.

This is achieved in presence of dissolved oxygen (DO) by oxidizing the micro-organisms (or bacteria) under the presence of light. So, more is the DO content, more will be the self-purification.

At higher temperature, the activity of micro-organisms are more as they are being oxidized more. Thus at a higher temperature, oxidation rate is more and so is the self-purification rate.

Sunlight has a bleaching action and it helps in photosynthesis of some water borne micro-organisms. They consumes CO2 and release O2, therefore increasing the DO content in the stream. So, the self-purification increases with the presence of sunlight.

Oxygen demand: Satisfying the oxygen demand means supplying the required DO for oxidation of micro-organisms. So, as the time gradually passes excess DO will present in the stream and it will increase self-purification capacity.

∴ Higher temperature, sunlight and satisfying oxygen demand all three will increase self-purification of streams.