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Select the correct statement from the following.
A
Activated sludge-sediment in settlement tanks of sewage treatment plant is a rich source of aerobic bacteria
B
Biogas is produced by the activity of aerobic bacteria on animal waste
C
$Methanobacterium$ is an aerobic bacterium found in rumen of cattle
D
Biogas, commonly called gobar gas, is pure methane
Detailed Solution
In secondary treatment, aerobic microbes grow in the aeration tanks as flocs (masses of bacteria associated with fungal filaments). When the effluent is passed into a settling tank these flocs sediment; this sediment is called activated sludge, so it is rich in aerobic bacteria. This statement is correct.
Biogas is produced by anaerobic bacteria (methanogens) acting on cellulosic material such as cattle dung.
$Methanobacterium$ is an anaerobic bacterium, found in anaerobic sludge and in the rumen of cattle.
Biogas is a mixture of gases, mainly methane with $CO_2$ and some $H_2$ and $H_2S$; it is not pure methane.
Hence the correct statement is the one about activated sludge.
Biogas is produced by anaerobic bacteria (methanogens) acting on cellulosic material such as cattle dung.
$Methanobacterium$ is an anaerobic bacterium, found in anaerobic sludge and in the rumen of cattle.
Biogas is a mixture of gases, mainly methane with $CO_2$ and some $H_2$ and $H_2S$; it is not pure methane.
Hence the correct statement is the one about activated sludge.