Question

11.
(a)
Mention the difference in the level of BOD before and after the
secondary treatment of sewage water.
Write the importance of flocs' during the secondary treatment of
sewage.
(b)
2
19​

Answer 1

a)

before secondary treatment the BOD of the sewage water is high

but as aerobic microbes grow during the secondary treatment they consume a large amount of oxygen thus reducing the BOD.

B)Flocs are masses of essential bacteria associated with fungal filaments to form a mesh-like structure. They are in a sludge structure. They help in increased aerobic decomposition as well as filament help in trapping particles when they are put in the secondary sewage tank