Match List-I with List-II
| List-I | List-II |
|---|---|
| Terms in sewage treatment | Features |
| (A) Flocs | (I) Large tank where bacteria grow anaerobically, digest the bacteria and the fungi in the sludge. |
| (B) BOD | (II) Effluent is passed into a settling tank where the bacterial ‘flocs’ are allowed to sediment |
| (C) Activated sludge | (III) Amount of the oxygen that would be consumed if all the organic matter in one liter of water were oxidised by bacteria. |
| (D) Anaerobic sludge digesters | (IV) Masses of bacteria associated with fungal filaments to form mesh like structures |
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → (A) - (IV), (B) - (III), (C) - (II), (D) - (I)
(A) Flocs — this matches (IV) Masses of bacteria associated with fungal filaments to form mesh like structures. In the aeration tanks, useful aerobic microbes grow vigorously and clump into these masses.
(B) BOD — this matches (III) Amount of the oxygen that would be consumed if all the organic matter in one liter of water were oxidised by bacteria. The more organic matter and microbes in the water, the more oxygen is used, so a high BOD means a more polluted water. Sewage treatment aims to lower it.
(C) Activated sludge — this matches (II) Effluent is passed into a settling tank where the bacterial ‘flocs’ are allowed to sediment. The sediment that settles is the activated sludge. A small part of it goes back to the aeration tank as inoculum.
(D) Anaerobic sludge digesters — this matches (I) Large tank where bacteria grow anaerobically, digest the bacteria and the fungi in the sludge. The rest of the activated sludge is pumped into these tanks, where biogas is also produced.
NCERT Extract:
Microbes in Sewage Treatment – “… This allows vigorous growth of useful aerobic microbes into flocs (masses of bacteria associated with fungal filaments to form mesh like structures).”
Microbes in Sewage Treatment – “… BOD refers to the amount of the oxygen that would be consumed if all the organic matter in one liter of water were oxidised by bacteria.”
Microbes in Sewage Treatment – “… Once the BOD of sewage or waste water is reduced significantly, the effluent is then passed into a settling tank where the bacterial ‘flocs’ are allowed to sediment. This sediment is called activated sludge. A small part of the activated sludge is pumped back into the aeration tank to serve as the inoculum. The remaining major part of the sludge is pumped into large tanks called anaerobic sludge digesters. Here, other kinds of bacteria, which grow anaerobically, digest the bacteria and the fungi in the sludge.”