NEET 2012 Biology question

The domestic sewage in large cities

(1)Have very high amounts of suspended solids and dissolved salts
(2)Has a high BOD as it contains both aerobic and anaerobic bacteria
(3)Is processed by aerobic and then anaerobic bacteria in the secondary treatment in Sewage Treatment Plants (STPs)Correct
(4)When treated in STPs does not really require the aeration step as the sewage contains adequate oxygen

Answer: (3)

Solution

In sewage treatment plants the primary treatment removes floating and suspended solids by filtration and sedimentation. In the secondary (biological) treatment the effluent is passed into aeration tanks where aerobic heterotrophic bacteria form flocs and reduce the BOD; the activated sludge is then taken to anaerobic

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Question ID VK-091052