# WASTE WATER Engineering Interview Questions

Posted On:February 1, 2019, Posted By: Latest Interview Questions, Views: 2300, Rating :

## Best WASTE WATER Engineering Interview Questions and Answers

Dear Readers, Welcome to WASTE WATER Engineering Interview Questions and Answers have been designed specially to get you acquainted with the nature of questions you may encounter during your Job interview for the subject of WASTE WATER Engineering. These WASTE WATER Engineering Questions are very important for campus placement test and job interviews. As per my experience good interviewers hardly plan to ask any particular questions during your Job interview and these model questions are asked in the online technical test and interview of many IT & Non IT Industries.

### For a continuous flow type of sedimentation tanks

A. Width of the tank is normally kept about 6 m

B. Length of the tank is normally kept 4 to 5 times the width

C. Maximum horizontal flow velocity is limited to 0.3 m/minute

D. All the above

ANS: D

### The asbestos cement sewers are

A. Light in weight

B. Not structurally strong to bear large compressive stress

C. Susceptible to corrosion by sulphuric acid

D. All the above

ANS: D

### For efficient working of a sewer, it must be ensured that

A. Minimum velocity of 0.45 m/sec, is maintained at its minimum flow

B. A maximum velocity of 0.90 m/sec, is maintained at its maximum flow

C. Both A. and B.

D. Neither A. nor B.

ANS: C

### Pick up the correct statement from the following:

A. The sewer pipes of sizes less than 0.4 m diameter are designed as running full at maximum discharge

B. The sewer pipes of sizes greater than 0.4 m diameter are designed as running 2/3rd or 3/4th full at maximum discharge

C. The minimum design velocity of sewer pipes is taken as 0.8 m/sec

D. All the above

ANS: D

Q No: 5

Pick up the correct statement from the following:

A. Maximum daily flow = 2 times the average daily flow

B. Maximum daily flow = average daily flow

C. Sewers are designed for minimum permissible velocity at minimum flow

D. All the above

ANS: D

A. 15 cm c/c

B. 22.5 cm c/c

C. 30 cm c/c

D. 50 cm c/c

ANS: B

### The pressure exerted by

A. The sewage when running full from inside, is called internal pressure

B. The internal pressure if any, causes tensile stress in the pipe material

C. Pressure sewers are designed to be safe in tension

D. All the above

ANS: D

### For drainage pipes in buildings the test applied before putting them to use, is

A. Water test

B. Smoke test

C. Straightness test

D. All the above

ANS: B

### No treatment of the sewage is given if dilution factor is

A. Less than 150

B. Between 150 to 200

C. Between 200 to 300

D. More than 500

ANS: D

### Which of the following pumps in used to pump sewage solids with liquid sewage without clogging the pump is?

A. Centrifugal pump

B. Pneumatic ejector

C. Reciprocating pump

D. None of these

ANS: A

### Acid regression stage of sludge digestion at a temperature 21°C extends over a period of

A. 15 days

B. 30 days

C. 60 days

D. 90 days ANS: D

### Pick up the correct statement from the following:

A. Small sewers are cleaned by flushing

B. Medium sewers are cleaned by cane rodding

C. Medium sewers may be cleaned by pills

D. All the above

ANS: D

### The coagulant which is generally not used for treating the sewage, is

A. Alum

B. Ferric chloride

C. Ferric sulphate

D. Chlorinated copperas

ANS: A

A. A heap

B. Plateau

C. Windrow

D. None of these

ANS: D

### If the flame of a miner’s safety lamp in the upper layers of the sewer forms an explosive, the sewer certainly contains

A. Hydrogen sulphide

B. Carbon dioxide

C. Methane

D. Oxygen

ANS: C

### The gas which may cause explosion in sewers, is

A. Carbondioxide

B. Methane

C. Ammonia

D. Carbon monoxide

ANS: B

### Pick up the correct statement from the following:

A. The water supply pipes carry pure water free from solid particles

B. The water supply pipes get clogged if flow velocity is less than self cleansing velocity

C. The sewers may be carried up and down the hills and valleys

D. The sewer pipes are generally laid along level hills

ANS: A

### Pick up the incorrect statement from the following:

A. The process of decomposing the organic matter under controlled anaerobic conditions, is called sludge digestion

B. Sludge digestion is carried out in sludge tank

C. The gases produced in sludge digestion process, contain 75% carbon dioxide

D. The gases produced in sludge digestion process, contain 75% methane

ANS: C

### The sewer pipes

A. Carry sewage as gravity conduits

B. Are designed for generating self-cleansing velocities at different discharge

C. Should resist the wear and tear caused due to abrasion

D. All the above

ANS: D

### The settling velocity of the particles larger than 0.06 mm in a settling tank of depth 2.4 is 0.33 m per sec. The detention period recommended for the tank, is

A. 30 minutes

B. 1 hour

C. 1 hour and 30 minutes

D. 2 hours

ANS: D

### The Chezy’s constant C in the formula V = C

A. Size of the sewer

B. Shape of the sewer

C. Roughness of sewer surface

D. All the above

ANS: D

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

A. Over flow rate

C. Over flow velocity

D. All the above

ANS: D

### 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

ANS: C

### 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 ANS: C

A. 0.50 m/sec

B. 0.60 m/sec

C. 0.70 m/sec

D. 0.75 m/sec

ANS: D

### 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

ANS: A

### 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

ANS: C

A. 0.10 cumec

B. 0.12 cumec

C. 0.15 cumec

D. 0.20 cumec

ANS: C

### 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

ANS: D

A. Fruhling

B. Lloyd David

C. Kuichling

D. All of these

ANS: D

A. Main sewer

B. Outfall sewer

C. Branch sewer

D. House sewer

ANS: B

### 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

ANS: D

A. 16 m

B. 20 m

C. 24 m

D. 30 m

ANS: C

### 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

ANS: D

### 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 ANS: D

### 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

ANS: D

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

A. Q = [(4 + )/(18 + )] q

B. Q = [(18 + P)/(4 + )] q

C. Q = [(18 + )/(4 + )] q

D. Q = [(5 + )/((15 + )] q

ANS: C

### 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

ANS: D

### 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

ANS: B

### Q No: 40

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

ANS: D

A. /2

B. /4

C. /3

D. D

ANS: C

### Pick up the correct statement from the following:

A. Anaerobic bacteria flourish in the absence of oxygen

B. Aerobic bacteria flourish in the presence of oxygen

C. Facultative bacteria flourish with or without oxygen

D. All the above

ANS: D

A. 10

B. 15

C. 20

D. 25

### Aerobic bacterias

A. Flourish in the presence of free oxygen

B. Consume organic matter as their food

C. Oxidise organic matter in sewage

D. All the above

ANS: D

### At the junction of sewers

A. Top of smaller sewer is kept lower

B. Top of larger sewer is kept lower

C. Tops of both the sewers are at the same level

D. None of these

ANS: D

### Traps

A. Are water seals which prevent the entry of foul gases

B. Are used to trap the rats entering sewers

C. Dissolve the foul gases

D. Create symphonic action to increase the quick disposal of sewerage

ANS: A

### The sewage treatment units in which anaerobic decomposition of organic matter is used, are called

A. Imhoff tanks

B. Trickling filters

C. Sludge sedimentation tanks

D. None of these

ANS: B

### Pick up the correct statement from the following:

A. In treated sewage, 4 ppm of D.O. is essential

B. Only very fresh sewage contains some dissolved oxygen

C. The solubility of oxygen in sewage is 95% that is in distilled water

D. All the above

ANS: D

### If the diameter of a sewer is 150 mm, the gradient required for generating self cleansing velocity, is

A. 1 in 60

B. 1 in 100

C. 1 in 120

D. None of these

ANS: B

### The sewer which received discharge from two or more main sewers, is known as

A. A trunk sewer

B. An outfall sewer

C. A main sewer

D. An intercepting sewer

ANS: A

### The grit and silt of the grit chambers, may not be used for

A. Raising low lying areas by dumping

B. Concreting

C. Both A. and B.

D. Neither A. nor B.

ANS: B

### For treating the sewage of a large city, you will recommend

A. A sedimentation tank and an activated sludge treatment plant

B. A plant consisting of Imhoff tanks with low rate trickling filters

C. Sedimentation tanks with high rate trickling filters

D. None of these

ANS: A

### Imhoff cone is used to measure

A. Total organic solids

B. Total solids

C. Total in organic solids

D. Settleable solids

ANS: D

### Pick up the correct statement from the following:

A. The ratio of the quantity of the diluting water to that of the sewage, is known as dilution factor

B. The automatic purification of polluted water, is known self purification phenomenon

C. The photosynthesis is carried out in the presence of sun light

D. All the above

ANS: D

### 1000 kg of sewage contains

A. 0.112 kg in suspension

B. 0.112 kg in solution

C. 0.225 kg in solution

D. Both A. and C. of above

ANS: D

### Dilution method of disposing of sewage, is not preferred to

A. When sewage is fresh

B. When diluting water has high dissolved oxygen content

C. When diluting water is used for water supply near the point of sewage disposed

D. When the diluting water is having flow currents

ANS: C

A. 100 cm

B. 90 cm

C. 80 cm

D. 50 cm

ANS: A

### The reduced levels of the string at the consecutive sight rails A and B are 203.575 m, 203.475 m respectively. If the difference of their R.D.s is 10 m, the gradient of the sewer line is

A. 1 in 100 upward

B. 1 in 500 upward

C. 1 in 100 downward

D. 1 in 503 upward

ANS: C

### R.M.O. expenses include

A. Running expenses

B. Maintenance expenses

C. Operation expenses

D. All the above

ANS: D

A. H2SO4

B. HNO3

C. HCl

D. None of these

ANS: A

A. Bath rooms

B. Wash basins

C. Kitchen sinks

D. Toilets

ANS: D

### In sewers the velocity of flow should not be

A. More than the self-cleansing velocity

B. Less than the self-cleansing velocity

C. Less than 10 m/sec

D. More than 20 m/sec

ANS: B

### Pick up the correct statement from the following:

A. Hydrogen sulphide gas in excess, may cause corrosion of concrete sewers

B. 4 ppm of Dissolved Oxygen (D.O.) is ensured before discharging the treated sewage in river

C. Solubility of oxygen in sewage is 95% of that of distilled water

D. All the above

ANS: D

### In sewers the effect of scouring is more on

A. Top side

B. Bottom side

C. Horizontal side

D. All sides

ANS: B

A. Its intensity

B. Its direction

C. Its frequency

D. All the above

ANS: D

### Pick up the correct statement from the following:

A. The circular section of sewers provides maximum hydraulic mean depth

B. The circular sewers are provided for separate sewerage system

C. The circular sewers work efficiently if the sections run at least half full

D. All the above

ANS: D

### Pick up the correct statement from the following:

A. Rate of digestion of sludge is more at higher temperature

B. Thermophilic organisms digest the sludge if the temperature ranges from 40° to 60°C

C. Mesophilic organisms digest the sludge if the temperature is between 25° and 40°C

D. All the above

ANS: D

### Sewer ventilating columns are generally placed at

A. Distances 150 m to 300 m

B. Upper ends of branch sewers

C. Every change in the size of sewers

D. All the above

ANS: D

### The sewer which resists sulphide corrosion, is

A. Brick sewer

B. Cast iron sewer

C. R.C.C. sewer

ANS: D

A. Q/(B × D)

B. Q/(L × D)

C. Q/L

D. Q/(B × L)

ANS: D

### The formula which accepts the value of rugosity coefficient n = 0.012 to be used in Manning’s formula, is given by

A. Bazin

B. Crimp and Bruges

C. William-Hazen

D. Kutter

ANS: B

### The amount of oxygen consumed by the aerobic bacterias which cause the aerobic biological decomposition of sewage, is known

A. Bio-Chemical Oxygen Demand (B.O.D.)

B. Dissolved Oxygen (D.O.)

C. Chemical Oxygen Demand (C.O.D.)

D. None of these

ANS: B

A. 90 %

B. 95 %

C. 99 %

D. 9.9 %

ANS: D

### Skimming tanks are

A. Used to remove the grease and oil

B. Those from which sludge is skimmed out

C. Tanks provided with self- cleansing screens

D. Improved version of grit chambers

ANS: A

A. Parabolic

B. Circular

C. Rectangular

D. New egged

ANS: B

### The detention period for plain sedimentation water tanks, is usually

A. 4 to 8 hours

B. 8 to 16 hours

C. 16 to 24 hours

D. 24 to 36 hours

ANS: A

### The factor responsible for purification of sewage in river is

A. Hydrology

B. Dissolved oxygen in water

C. Temperature

D. All the above

ANS: D

### Hume steel pipes are

A. Steel pipes

B. Steel shell coated from inside with cement mortar

C. Steel shell coated from outside with cement mortar

D. Both B. and C.

ANS: D

A. 45 %

B. 50 %

C. 55 %

D. 60 %

ANS: C

### Pick up the correct statement from the following:

A. The larger the sewer in size, more will be velocity

B. The smaller the sewer in size, less will be velocity

C. The larger the sewer in size, no deposition will take place

D. The larger the sewer in size, deposition will take place

ANS: D

A. Imhoff Cone

B. Turbid meter

C. Potentiometer

D. None of these

ANS: C

A. 2 hours

B. 4 hours

C. 6 hours

D. 8 hours

ANS: D

### The normal value of over flow rates for plain primary sedimentation tanks, 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

ANS: B

### Pick up the incorrect statement from the following:

A. Septic tanks are horizontal continuous flow type of sedimentation tanks

B. Septic tanks are generally provided a detention period of 12 to 36 hours

C. Septic tanks are completely covered and high vent shafts are provided for the escape of foul gases

D. None of these

ANS: D

### 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

ANS: D

### In a trickling filter

A. Filtration process is used

B. Biological action is used

C. Neither A. nor B.

D. Both A. and B.

ANS: B

### In areas where rainy season is limited to a few months, the type of sewerage system recommended is

A. Combined system

B. Partially separate system

C. Separate system

D. None of these

ANS: C

### 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

ANS: A

### Dried sewage after treatment is used as

A. Fertilizer

B. Building material

C. Chemical for lowering B.O.D.

D. Base material for paints

ANS: A

A. d = 0.2 B

B. d = 0.5 B

C. B = 0.2 d

D. B = 0.5 d

ANS: B

### In areas where light rains are uniformly distributed throughout the year, the type of sewerage system to be adopted is

A. Separate system

B. Combined system

C. Partially combined system

D. None of these

ANS: B

### Self-cleansing velocity is

A. Velocity at dry weather flow

B. Velocity of water at flushing

C. Velocity at which no accumulation remains in the drains

D. Velocity of water in a pressure filter

ANS: C

A. 0°C

B. 15°C

C. 20°C

D. 25°C

ANS: C

### Pick up the correct statement from the following:

A. Inlets are provided on the road surface at the lowest point for draining rain water

B. Inlets are generally provided at an interval of 30 m to 60 m along straight roads

C. Inlets having horizontal openings, are called horizontal inlets

D. All the above

ANS: D

A. 100 mg/l

B. 200 mg/l

C. 300 mg/l

D. 400 mg/l

ANS: D

### Pick up the in-correct statement from the following:

A. Manholes are provided in sewer pipes at suitable intervals

B. Catch basins are generally provided in sewers for carrying drainage discharge

C. Inlets are generally provided in all sewers

D. None of these

ANS: C

A. Nitrates

B. Nitrites

C. Free ammonia

D. None of these

ANS: A

A. 25 %

B. 50 %

C. 10 %

D. 5 %

ANS: B

### In a sludge tank, the gas mainly produced, is

A. Oxygen

B. Nitrogen

C. Hydrogen

D. Carbon dioxide

ANS: D

### Bio-chemical oxygen demand (BOD) for the first 20 days in generally referred to

A. Initial demand

B. First stage demand

C. Carbonaceous demand

D. All of these

ANS: D