Read the following statements & about waste water treatment how many of them are correct
(i) In Primary treatment First, floating debris of waste is removed by sequence filters
(ii) The Soil and small pebbles are removed by sedimentation in settling tanks
(iii)The sediment is called primary sludge and supernatant is effluent.
(iv) The Sludge is taken for Secondary treatment.
(v) Lower the B.O.D., higher Is water pollution.
(vi)When DDT enters the food chain then they reach water and are easily degradable.
(vii)Discharge of sewage water into river water will decrease its B.O.D.
(viii) Chlorine is added to disinfect drinking water

(i), (ii), (iii), (iv)

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(i), (ii), (iii), (vii)

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(i), (ii) (iv), (v)

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(i),(iv),(v), (viii)

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Solution

The correct option is B (i), (ii), (iii), (iv)
Treatment of wastewater is done by the heterotrophic microbes naturally present in the sewage.
This treatment is carried out in two stages:
Primary treatment: These treatment steps basically involve physical removal of particles large and small from the sewage through filtration and sedimentation. Initially, floating debris is removed by sequential filtration. Then the grit (soil and small pebbles) are removed by sedimentation. All solids that settle form the primary sludge and the supernatant forms the effluent. The effluent from the primary settling tank is taken for secondary treatment.
Secondary treatment or Biological treatment: The primary effluent is passed into large aeration tanks.
Hence, (i) In Primary treatment First, floating debris of waste is removed by sequence filters (ii) The Soil and small pebbles are removed by sedimentation in settling tanks (iii)The sediment is called primary sludge and supernatant is affluent. (iv) The Sludge is taken for Secondary treatment following statements & about wastewater treatment are correct.

So, the correct answer is '(i), (ii), (iii), (iv)'.

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Similar questions

Q. Study the following statements and select the incorrect ones.

(i) Physical removal of large and small particles through filtration and sedimentation is called primary sewage treatment.
(ii) Secondary sewage treatment is mainly a mechanical process.
(iii) Activated sludge sediment in a sewage treatment plant is a rich source of aerobic bacteria.
(iv) Biogas, commonly called as gobar gas, is pure methane.

Q. How many of the following statements are correct with respect to the activated sludge?

I - It is composed of soil and small pebbles that are removed during the primary treatment of the sewage
II - It can be used for biogas production
III - It is fed into anaerobic sludge digesters
IV - It is obtained at the end of the oxidation of organic wastes during the secondary treatment of the sewage

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Some students of class 7 were taken for an educational trip to Waste water treatment plant .The teacher explained the process of water treatment. Identify the correct order of the process.

Step I:The liquid material is passed through sedimentation tank where solid waste like faecal matter, sand, grit settles down.

Step II:This solid matter is then removed with the help of a scrapper. This is the sludge.

Step III: Waste water is passed through bar screens to remove big objects like cans, sticks, rags etc.

Step IV: A skimmer removes the floatable solids like oil, grease etc.

Step V: Air is pumped into clarified water to help aerobic bacteria to grow. The bacteria then consume the unwanted matter still present in clarified water.

Step VI: The clear water so obtained is called clarified water.

Step VII:The suspended microbes settle at the bottom & the water is removed from the top.

Q. Refer the given flowchart of sewage treatment, accordingly match Column I with Column II and select the correct answer from the codes given below:

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