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प्रश्न
Three water samples namely river water, untreated sewage water and secondary effluent discharged from a sewage treatment plant were subjected to BOD test. The samples were labelled A, B and C; but the laboratory attendant did not note which was which. The BOD values of the three samples A, B and C were recorded as 20 mg/L, 8 mg/L and 400 mg/L, respectively. Which sample of the water is most polluted? Can you assign the correct label to each, assuming the river water is relatively clean?
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उत्तर
Biological oxygen demand (BOD) is the method of determining the amount of oxygen required by micro-organisms to decompose the waste present in the water supply. If the quantity of organic waste in the water supply is high, then the number of decomposing bacteria present in the water will also be high. As a result, the BOD value will increase.
Therefore, it can be concluded that if the water supply is more polluted, then it will have a higher BOD value. Out of the above three samples, sample C is the most polluted since it has the maximum BOD value of 400 mg/L. After untreated sewage water, secondary effluent discharge from a sewage treatment plant is most polluted. Thus, sample A is secondary effluent discharge from a sewage treatment plant and has the BOD value of 20 mg/L, while sample B is river water and has the BOD value of 8 mg/L.
Hence, the correct label for each sample is:
| Label | BOD value | Sample |
| A | 20 mg/L | Secondary effluent discharge from a sewage treatment plant |
| B | 8 mg/L | River water |
| C | 400 mg/L | Untreated sewage water |
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संबंधित प्रश्न
Explain the role of microbes in sewage treatment.
What is sewage?
Describe how do 'flocs' and 'activated sludge' help in Sewage Treatment.
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Name the tank to which the sewage water is passed after the preliminary treatment?
Which of the following is TRUE about primary treatment?
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What happens during the course of sewage decomposition?
Study the following statements regarding tertiary treatment of sewage and choose the correct option.
i. It produces methane gas.
ii. The effluents formed from these plants undergo chlorination.
iii. BOD is significantly increased at this step.
iv. It includes screening and passage of effluent through grit chamber.
After which of the following treatment BOD of the effluent is significantly reduced?
Which of the following is TRUE regarding 'Flocs'?
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The primary treatment of waste water involves the removal of ______.
Name the states involved in Ganga action plan.
What is the group of bacteria found in both the rumen of cattle and shidge of sewage treatment?
Why are flocs important in biological treatment of waste water?
Ganga has recently been declared the national river. Discuss the implication with respect to pollution of this river.
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Study the given diagram of the Sewage Treatment Plant (S.T.P.) and answer the question that follows:
- Which one of the two 'S.T.P.' (A) or (B) will be more effective in treating the human excreta in municipal waste?
- Write the steps followed in carrying the treatment of the sewage in step (Z), once the BOD of sewage is reduced significantly till it is passed on to the "anaerobic sludge digesters".
Which one is wrongly matched?
After a significant reduction in the BOD of wastewater, it is passed into a settling tank where bacterial flocs are allowed to sediment. This sediment is called ______.
Which of the following statement is correct for Sewage Treatment Plants (STPs)?
