NPTEL Introduction to Environmental Engineering and Science-ASS9

In a BOD test, the initial DO of the 3% diluted sample is 9 mg/l, and its final DO after 5 days of incubation at 20 °C is 3 mg/l. Find the 5-day BOD of the sewage sample.

• 100 mg/L

• 150 mg/L

• 200 mg/L

• 250 mg/L

What is the BOD5 of industrial sewage if the Population equivalent of that wastewater is 5000 persons?

• 200 kg/day

• 400 kg/day

• 600 kg/day

• 800 kg/day

Find the diameter of the standard trickling filter if the influent BOD is 250 mg/L and the desired effluent BOD is 25 mg/L, to handle 3 MLD of waste water flow. Assume depth = 3m.

• 46 m

• 86 m

• 71 m

• 40 m

Match the following;

A. Preliminary treatment i. Chlorination

B. Primary treatment ii. Activated sludge process

C. Secondary treatment iii. Screening

D. Tertiary treatment iv. Sedimentation tank

• A-iii, B-iv, C-ii, D-i

• A-iii, B-iv, C-i, D-ii

• A-i, B-iv, C-ii, D-iii

• A-ii, B-iv, C-iii, D-i

Which preliminary treatment unit is designed to remove oils or greases from wastewater?

• Screening

• Equalization tank

• Detritus tank

• Skimming tank

Which is the structure designed for maintaining a constant flow velocity in grit chambers?

• Spiral aerator

• Equalization basin

• Parshall flume

• Screens

Identify the correct order for the arrangement of solids in their increasing size.

• Dissolved solids < Suspended solids < Colloidal solids

• Dissolved solids < Colloidal solids < Suspended solids

• Colloidal solids < Dissolved solids < Suspended solids

• Colloidal solids < Suspended solids < Dissolved solids

State whether the following statement is True/False. "If BOD5 / COD varies between 0.63 and 0.68, then the wastewater can be considered to be fully biodegradable."

• True

• False

Which of the following statements is not true for a Separate sewerage system?

• Sewerage being small, difficulty in cleaning them

• Frequent choking problem

• System proves costly as it involves two sets of sewers

• Sewage load on treatment unit is high

Identify the wrong statement regarding the grit chamber from the following.

• Grit chambers are provided to reduce maintenance cost in high-speed centrifuges, which needs almost all grit particles to be removed.

• Grit chambers are designed to separate out the grit, gravel, sand, egg, sells etc. of size 2 mm or larger.

• It is a settling tank with lesser detention time of 1 min and flow velocity of 0.2 to 0.3 m/sec.

• Low flow velocity has to be maintained inside a grit chamber for efficient settling of grit particles.