Waste Water Engineering -2

Question No. 21

The Chezy's constant C in the formula V = C √rs depends upon

(A) Size of the sewer

(B) Shape of the sewer

(C) Roughness of sewer surface

(D) All the above

Answer: Option D

Question No. 22

The discharge per unit plan area of a sedimentation tank, is generally called

(A) Over flow rate

(B) Surface loading

(C) Over flow velocity

(D) All the above

Answer: Option D

Question No. 23

Pick up the incorrect statement from the following for allowing workers to enter sewers

(A) The particular manhole and one manhole on upstream and one manhole on downstream

should remain open for 30 minutes

(B) Proper tests for the presence of poisonous gases must be carried out

(C) The men entering the manhole should be advised to smoke in the sewer

(D) Warning signals should be erected

Answer: Option C

Question No. 24

For the open drain (N = 0.025) shown in the below figure, the discharge is

(A) 26.88 cumecs

(B) 27.88 cumecs

(C) 28.88 cumecs

(D) 29.88 cumecs

Answer: Option C

Question No. 25

To prevent settling down of sewage both at the bottom and on the sides of a large sewer, selfcleaning

velocity recommended for Indian conditions, is

(A) 0.50 m/sec

(B) 0.60 m/sec

(C) 0.70 m/sec

(D) 0.75 m/sec

Answer: Option D

Question No. 26

Assertion (A): The determination of pH value of sewerage is important.

Reason (R): The efficiency of certain treatment methods depends upon the availability of pH value.

(A) Both A and R are true and R is the correct explanation of A

(B) Both A and R are true but R is not a correct explanation of A

(C) A is true but R is false

(D) A is false but R is true

Answer: Option A

Question No. 27

The normal values of over flow rates for sedimentation tanks using coagulant, ranges between

(A) 25,000 to 35,000 litres/sqm/day

(B) 40,000 to 50,000 litres/sqm/day

(C) 50,000 to 60,000 litres/sqm/day

(D) 80,000 to 100,000 litres/sqm/day

Answer: Option C

Question No. 28

The drainage area of a town is 12 hectares. Its 40% area is hard pavement (K = 0.85), the 40% area

is unpaved streets (K = 0.20) and the remaining is wooded areas (K = 0.15). Assuming the time of

concentration for the areas as 30 minutes and using the formula Ps = 900/(t + 60) the maximum

run off is

(A) 0.10 cumec

(B) 0.12 cumec

(C) 0.15 cumec

(D) 0.20 cumec

Answer: Option C

Question No. 29

Sewer pipes are designed for maximum discharge with 25% to 33% vacant cross-sectional area for

(A) Unexpected large scale infiltration of stream water

(B) Unexpected increase in the population

(C) Under estimates of maximum and average flows

(D) All of the above

Answer: Option D

Question No. 30

The rational formula for peak drainage discharge, was evolved by

(A) Fruhling

(B) Lloyd David

(C) Kuichling

(D) All of these

Answer: Option D

Question No. 31

The sewer that unloads the sewage at the point of treatment is called

(A) Main sewer

(B) Outfall sewer

(C) Branch sewer

(D) House sewer

Answer: Option B

Question No. 32

During preliminary treatment of a sewage

(A) Oil and grease are removed from skimming tanks

(B) Floating materials are removed by screening

(C) Girt and sand are removed by girt chambers

(D) All the above

Answer: Option D

Question No. 33

For a grit chamber, if the recommended velocity of flow is 0.2 m/sec and detention period is 2

minutes, the length of the tank, is

(A) 16 m

(B) 20 m

(C) 24 m

(D) 30 m

Answer: Option C

Question No. 34

Dry weather flow is:

(A) Average daily rate of flow

(B) Average monthly rate of flow

(C) Average annual rate of flow

(D) Water supply allowance per capita

Answer: Option D

Question No. 35

Pick up the incorrect statement from the following:

(A) The mixture of water and waste products, is called sewage

(B) The treated sewage effluents, are generally used for irrigating the crops

(C) The process of collecting, treating and disposing off the sewage, is called sewerage

(D) The old convergence system was definitely better than water carried sewerage system

Answer: Option D

Question No. 36

Pick up the correct statement from the following:

(A) The maximum rate of storm runoff is called peak drainage discharge

(B) Rational method of estimating peak run off, may be used precisely for areas less than 50

hectares

(C) The period after which the entire area starts contributing to the runoff, is called the time of

concentration

(D) All the above

Answer: Option D

Question No. 37

If q is the average sewage flow from a city of population P, the maximum sewage flow

(A) Q = [(4 + √P)/(18 + √P)] q

(B) Q = [(18 + P)/(4 + √P)] q

(C) Q = [(18 + √P)/(4 + √P)] q

(D) Q = [(5 + √P)/((15 + √P)] q

Answer: Option C

Question No. 38

¾th or ¼th extra space is left in sewer pipes at maximum discharge for

(A) Low estimates of the average and maximum flows

(B) Large scale infiltration of storm water

(C) Unexpected increase in population

(D) All the above

Answer: Option D

Question No. 39

If the flame of a miner's safety lamp in a manhole extinguishes within 5 minutes, the sewer

certainly contains

(A) Hydrogen sulphide

(B) Carbon dioxide

(C) Methane

(D) Oxygen

Answer: Option B

Question No. 40

Hydraulic mean radius is

(A) Mean radius of sewer

(B) Difference in heads between two points in circular pipes

(C) Mean of radii in a pipe line of varying cross-sections

(D) Cross-sectional area/wetted perimeter

Answer: Option D