The sewage treatment in septic tanks is due to

The bottom of the sewage inlet chamber of septic tanks, is provided an outward slope

A

1 in 5

B

1 in 10

C

1 in 15

D

1 in 20

During sewage treatment, the sewage is subjected to __________ treatment in Imhoff tank.

A

Filtration

B

Digestion

C

Sedimentation

D

Both B and C

Which one of the following statements regarding septic tanks is wrong?

A

A gap of 7.5 cm between the bottom of the covering slab and the top level of scum is provided

B

The outlet invert level is kept 5 to 7.5 cm below the inlet invert level

C

The minimum width of septic level is 90 cm

D

The depth of tank is kept equal to its width

Septic tanks are used for the __________ of the deposited solids.

A

Separation

B

Anaerobic decomposition

C

Aerobic decomposition

D

None of these

In septic tanks,

A

Free board of 0.3 m may be provided

B

The baffles or tees are extended up to top level of scum

C

The clear space between the baffle top and covering slab is about 7.5 cm

D

All the above

The rate of accumulation of sludge in septic tanks is recommended as

A

30 litres/person/year

B

25 litres/person/year

C

30 litres/person/month

D

25 litres/person/month

The digested sludge from septic tanks, is removed after a maximum period of

A

3 years

B

3.5 years

C

4 years

D

5 years

In septic tanks, decomposition of organic bacteria, is done by

A

Anaerobic bacteria

B

Aerobic bacteria

C

Both types of bacterias

D

None of these

Fine grit present in sewage is removed in the __________ during sewage treatment.

A

Grit chamber

B

Detritus tank

C

Trickling filter

D

Skimming tank

__________ substances present in sewage are removed in grit chamber during sewage treatment.

A

Organic

B

Fatty

C

Inorganic

D

Dissolved

The sewage treatment in septic tanks is due to

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