150 TOP ENVIRONMENTAL Engineering Objective Type Questions and Answers

ENVIRONMENTAL Engineering Objective Type Questions and Answers pdf :-

1. Assertion A : The consumption of water increases with increase in the distribution pressure.
Reason R : Higher distribution pressure causes more loss and waste of water.
Select your answer according to the coding system given below
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 the correct explanation of A.
c) A is true but R is false.
d) A is false but R is true.
Ans: a

2. The per capital consumption of a locality is affected by
i) climatic conditions
ii) quality of water
iii) distribution pressure
The correct answer is
a) only (i)
b) both (i) and (ii)
c) both (i) and (iii)
d) all (i), (ii) and (iii)
Ans: d

3. Which of the following causes a decrease in per capita consumption ?
a) use of metering system
b) good quality of water
c) better standard of living of the people
d) hotter climate

4. The hourly variation factor is usually taken as
a) 1.5
b) 1.8
c) 2.0
d) 2.7

5. If the average daily consumption of a city is 100,000 m3, the maximum daily con¬sumption on peak hourly demand will be
a) 100000m3
b) 150000m3
c) 180000m3
d) 270000 m3

6. The distribution mains are designed for
a) maximum daily demand
b) maximum hourly demand
c) average daily demand
d) maximum hourly demand on maxi¬mum day

7. As compared to geometrical increase method of forecasting population, arithmetical increase method gives
a) lesser value
b) higher value
c) same value
d) accurate value

8. The population of a town in three consecutive years are 5000, 7000 and 8400 respectively. The population of the town in the fourth consecutive year according to geometrical increase method is
a) 9500
b) 9800
c) 10100
d) 10920

9. The suitable method of forecasting popu¬lation for a young and rapidly increasing city is
a) arithmetical increase method
b) geometrical increase method
c) incremental increase method
d) graphical method

10., The depression of water table in a well due to pumping will be maximum
a) at a distance R from the well
b) close to the well
c) at a distance R/2 from the well
d) none of the above
where R is the radius of influence

11. The devices which are installed for drawing water from the sources are called
a) aquifers
b) aquiclude
c) filters
d) intakes

12. Select the correct relationship between porosity (N), specific yield (y) and specific retention (R)
a) N = y + R
b) y = N + R
c) R = N + y
d) R > (N + y)

13. The type of valve, which is provided on the suction pipe in a tube-well, is
a) air relief valve
b) reflux valve
c) pressure relief valve
d) sluice valve

14. The maximum discharge of a tube-well is about
a) 5 litres/sec
b) 50 litres/sec
c) 500 litres/sec
d) 1000 litres/see

15. As compared to shallow-wells, deep wells have
a) more depth
b) less depth
c) more discharge
d) less discharge

16. Ground water is usually free from
a) suspended impurities
b) dissolved impurities
c) both suspended and dissolved impuri¬ties
d) none of the above

17. The polluted water is one which
a) contains pathogenic bacteria
b) consists of undesirable substances rendering it unfit for drinking and domestic use
c) is safe and suitable for drinking and domestic use
d) is contaminated

18. Which of the following is not a water borne disease ?
a) dysentery
b) cholera
c) typhoid
d) maleria

19. The most common cause of acidity in water is
a) carbon dioxide
b) oxygen
c) hydrogen
d) nitrogen

20. The phenolic compounds in public water supply should not be more than
a) 0.1 ppm
b) 0.01 ppm
c) 0.001 ppm
d) 0.0001 ppm

21. The maximum permissible limit for flouride in drinking water is
a) 0.1 mg/litre
b) 1.5 mg/litre
c) 5 mg/litre
d) 10 mg/litre

22. Standard EDTA (ethylene diamine tetra acetic acid) solution is used to determine the
a) hardness in water
b) turbidity in water
c) dissolved oxygen in water
d) residual chlorine in water

23. If the coliform bacteria is present in a sample of water, then the coliform test to be conducted is
i) presumptive coliform test
ii) confirmed coliform test
iii) completed coliform test The correct answer is
a) only (i)
b) both (i) and (ii)
c) both (i) and (iii)
d) all (i), (ii) and (iii)

24. Alkalinity in water is expressed as milli-grams per litre in terms of equivalent
a) calcium carbonate
b) magnesium carbonate
c) sodium carbonate
d) calcium hydroxide

26. Which of the following values of pH represents a stronger acid?
a) 2
b) 5
c) 7
d) 10

27. Turbidity is measured on
a) standard silica scale
b) standard cobalt scale
c) standard platinum scale
d) platinum cobalt scale

28. On standard silica scale, the turbidity in drinking water should be limited to
a) 10 ppm
b) 20 ppm
c) 30 ppm
d) 50 ppm

29. Residual chlorine in water is determined by
a) starch iodide method
b) orthotolidine method
c) both (a) and (b)
d) none of the above

30. Orthotolidine test is used for determination of
a) dissolved oxygen
b) residual chlorine
c) biochemical oxygen demand
d) dose of coagulant

31. If the total hardness of water is greater than its total alkalinity, the carbonate hardness will be equal to
a) total alkalinity
b) total hardness
c) total hardness – total alkalinity
d) non carbonate hardness

32. The amount of residual chlorine left in public water supply for safety against pathogenic bacteria is about
a) 0.01 to 0.05 ppm
b) 0.05 to 0.5 ppm
c) 0.5 to 1.0 ppm
d) 1.0 to 5.0 ppm

33. The dissolved oxygen level in natural unpolluted waters at normal temperature is found to be of the order of
a) 1 mg/litre
b) 10 mg/litre
c) 100 mg/litre
d) 1000 mg/litre

34. The velocity of flow of water in a sedimentation tank is about
a) 5 to 10 cm/sec.
b) 15 to 30 cm/sec.
c) 15 to 30 cm/minute
d) 15 to 30 cm/hour

35. The length of rectangular sedimentation tank should not be more than
a) B
b) 2B
c) 4B
d) 8B
where B is the width of the tank

36. The overflow rate for plain sedimentation tanks is about
a) 500 to 750 litres/hour/ m2
b) 1000 to 1250 litres/hour/ m2
c) 1250 to 1500 litres/hour/m2
d) 1500 to 2000 litres/hour/m2

37. Percentage of bacterial load that can be removed from water by the process of plain sedimentation is about
a) 10 to 25
b) 50
c) 75
d) 100

38. The settling velocity of a particle in a sedimentation tank depends on
a) depth of tank
b) surface area of tank
c) both depth and surface area of tank
d) none of the above

39. The settling velocity of a particle in a sedimentation tank increases if
a) particle size is decreased
b) the surface area of tank is increased
c) the depth of tank is decreased
d) none of the above

40. For a given discharge, the efficiency of sedimentation tank can be increased by
a) increasing the depth of tank
b) decreasing the depth of tank
c) increasing the surface area of tank
d) decreasing the surface area of tank

41. The detention period and overflow rate respectively for plain sedimentation as compared to sedimentation with coagulation are generally
a) less and more
b) less and less
c) more and less
d) more and more

42. The amount of coagulant needed for coagulation of water increases with
i) increase in turbidity of water
ii) decrease in turbidity of water
iii) increase in temperature of water
iv) decrease in temperature of water
The correct answer is
a) (i) and (ii)
b) (i)and(iv)
c) (ii) and (iii)
d) (ii) and (iv)

43. Alum as a coagulant is found to be most effective when pH range of water is
a) 2 to 4
b) 4 to 6
c) 6 to 8
d) 8 to 10

44. The detention period in coagulation tanks is usually kept as
a) 1 to 2 minutes
b) 30 to 45 minutes
c) 2 to 6 hours
d) 2 to 6 days

45. The alum, when added as a coagulant in water
a) does not require alkalinity in water for flocculation
b) does not affect pH value of water
c) increases pH value of water
d) decreases pH value of water

46. The chemical most commonly used to increase speed of sedimentation of sewage is
a) sulphuric acid
b) copper sulphate
c) lime
d) sodium permanganate

47. In water treatment, rapid gravity filters are adopted to remove
a) dissolved organic substances
b) dissolved solids and dissolved gases
c) floating solids and dissolved inorganic solids
d) bacteria and colloidal solids

48. The rate of filtration in slow sand filters in million litres per day per hectare is about
a) 50 to 60
b) 100 to 150
c) 500 to 600
d) 1400 to 1500

49. The effective size of sand particles used in slow sand filters is
a) 0.25 to 0.35 mm
b) 0.35 to 0.60 mm
c) 0.60 to 1.00 mm
d) 1.00 to 1.80 mm

50. As compared to rapid sand filters, slow sand filters give
i) slower filtration rate
ii) higher filtration rate
iii) lesser efficiency in removal of bacteria
iv) higher efficiency in removal of bacteria The correct answer is
a) (i) and (ii)
b) (ii) and (iii)
c) (i) and (iv)
d) (ii) and (iv)

51. Assertion A: Slow sand filters are more efficient in removal of bacteria than rapid sand filters.
Reason R : The sand used in slow sand filters is finer than that in rapid sand filters.
Select your answer based on the coding system given below:
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 the correct explanation of A.
c) A is true but R is false.
d) A is false but R is true.

52. Air binding phenomena in rapid sand filters occur due to
a) excessive negative head
b) mud ball formation
c) higher turbidity in the effluent
d) low temperature

53. The percentage of filtered water, which is used for backwashing in rapid sand filters, is about
a) 0.2 to 0.4
b) 0.4 to 1.0
c) 2 to 4
d) 5 to 7

54. Period of cleaning of slow sand filters is about
a) 24 – 48 hours
b) 10-12 days
c) 2-3 months
d) 1-2 year

55. The rate of Alteration of pressure filters is
a) less than that of slow sand filters
b) in between the filtration rate of slow sand filters and rapid sand filters
c) greater than that of rapid sand filters
d) equal to that of slow sand filters

56. Double filtration is used
a) to increase the filtration slow sand filters capacity of
b) to increase the filtration rapid sand filters capacity of
c) for isolated buildings like pools, hotels etc swimming
d) all of the above

57. Cleaning is done by
i) scraping and removal in filters slow sand
ii) back washing in slow sand filters
iii) scraping and removal in filters rapid sand
iv) back washing in rapid sand filters
The correct answer is
a) (i) and (ii)
b) (ii) and (iii)
c) (i) and (iv)
d) (ii) and (iv)

58. Disinfection of water results in
a) removal of turbidity
b) removal of hardness
c) killing of disease bacteria
d) complete sterilisation

59. The disinfection efficiency of chlorine increases by
i) decreasing the time of contact
ii) decreasing the temperature of water
iii) increasing the temperature of water The correct answer is
a) only (i)
b) both (i) and (ii)
c) both (i) and (iii)
d) only (iii)

60. Chlorine demand of water is equal to
a) applied chlorine
b) residual chlorine
c) sum of applied and residual chlorine
d) difference of applied and residual chlorine

61. The process in which the chlorination is done beyond the break point is known as
a) prechlorination
b) post chlorination
c) super chlorination
d) break point chlorination

62. The percentage of chlorine in fresh bleaching powder is about
a) 10 to 15
b) 20 to 25
c) 30 to 35
d) 40 to 50

63. The treatment of water with bleaching powder is known as
a) prechlorination
b) super chlorination
c) dechlorination
d) hypochlorination

64. The suitable method for disinfection of swimming pool water is
a) ultra violet rays treatment
b) lime treatment
c) by using potassium permanganate
d) chlorination

65. Which of the following chemical compounds can be used for dechlorination of water ?
a) carbon dioxide
b) bleaching powder
c) sulphur dioxide
d) chloramines

66. In chlorination, with the rise in temperature of water, death rate of bacteria
a) increases
b) decreases
c) remains unaffected
d) none of the above

67. As compared to higher pH values, the contact period required for efficient chlorination at lower pH values is
a) smaller
b) larger
c) same
d) none of the above

68. Disinfection efficiency is
a) reduced at higher pH value of water
b) unaffected by pH value of water
c) increased at higher pH value of water
d) highest at pH value equal to 7

69. In lime-soda process
a) only carbonate hardness is removed
b) only non-carbonate hardness is re-moved
c) lime reduces the carbonate hardness and soda-ash removes the non-carbo¬nate hardness
d) lime reduces the non-carbonate hard-ness and soda-ash removes the carbo¬nate hardness

70. The major disadvantage of lime soda process of water softening is that
a) it is unsuitable for turbid and acidic water
b) huge amount of precipitate is formed which creates a disposal problem
c) the effluent cannot be reduced to zero hardness
d) it is unsuitable for softening the water of excessive hardness

71. Which of the following compounds is widely used for algae control ?
a) sodium sulphate
b) copper sulphate
c) sodium chloride
d) calcium chloride

72. Activated carbon is used for
a) disinfection
b) removing hardness
c) removing odours
d) removing corrosiveness

73. As compared to cast iron pipes, steel pipes are
a) heavier
b) stronger
c) costlier
d) less susceptible to corrosion

74. The suitable layout of a distribution system for irregularly growing town is
a) dead end system
b) grid iron system
c) radial system
d) ring system

75. The layout of distribution system in which water flows towards the outer periphery is
a) ring system
b) dead end system
c) radial system
d) grid iron system

Environmental Engineering Interview Questions

76. The suitable layout of distribution system for a city with roads of rectangular pattern is
a) grid iron system
b) dead end system
c) ring system
d) radial system

77. The commonly used material for water supply pipes, which has the properties of being strong, not easily corroded and long life but is heavy and brittle is
a) steel
b) cast iron
c) copper
d) reinforced cement concrete

78. Hardy cross method of analysis of distribution system
i) involves successive trials
ii) takes economic aspects into account
iii) is time consuming
The correct answer is
a) only (i)
b) (i)and(ii)
c) (i) and (iii)
d) all are correct

79. The method of analysis of distribution system in which the domestic supply is neglected and fire demand is considered is
a) circle method
b) equivalent pipe method
c) electrical analysis method
d) Hardy cross method

80. Which of the following methods of analysis of water distribution system is most suitable for long and narrow pipe
system ?
a) circle method
b) equivalent pipe method
c) Hardy cross method
d) electrical analysis method

81. The type of valve which is provided to control the flow of water in the distribution system at street corners and where the pipe lines intersect is
a) check valve
b) sluice valve
c) safety valve
d) scour valve

82. The type of valve which allows water to flow in one direction but prevents its flow in the reverse direction is
a) reflux valve
b) sluice valve
c) air relief valve
d) pressure relief valve

83. Scour valves are provided
a) at street corners to control the flow of water
b) at every depression and dead ends to drain out the waste water that may collect there
c) at the foot of rising main along the slope to prevent back running of water
d) at every summit of rising mains

84. A sewer that receives the discharge of a number of house sewers is called
a) house sewer
b) lateral sewer
c) intercepting sewer
d) submain sewer

85. A pipe conveying sewage from plumbing system of a single building to common sewer or point of immediate disposal is called
a) house sewer
b) lateral sewer
c) main sewer
d) submain sewer

86. For a country like India, where rainfall is mainly confined to one season, the suitable sewerage system will be
a) separate system
b) combined system
c) partially combined system
d) partially separate system

87. Average rate of water consumption perhead per day as per Indian Standard is
a) 100 litres
b) 135 litres
c) 165 litres
d) 200 litres

88. Sewerage system is usually designed for
a) 10 years
b) 25 years
c) 50 years
d) 75 years

89. Which of the following sewers is preferred for combined system of sewage ?
a) circular sewer
b) egg shaped sewer
c) rectangular sewer
d) none of the above

90. The suitable system of sanitation for area of distributed rainfall throughout the year with less intensity is
a) separate system
b) combined system
c) partially separate system
d) partially combined system

91. The water carriage system of collection of waste product
a) is cheaper in initial cost than dry conservancy system
b) requires treatment before disposal
c) creates hygenic problem
d) all of the above

92. If the time of concentration is 9 minutes, then the intensity of rainfall according to British Ministry of Health formula will be
a) 4 mm/hr
b) lOmm/hr
c) 20 mm/hr
d) 40 mm/hr

93. The time of concentration is defined as
a) the time taken by rainfall water to run from most distant point of water shed to the inlet of sewer
b) the time required for flow of water in sewer to the point under consideration
c) sum of (a) and (b)
d) difference of (a) and (b)

94. The specific gravity of sewage is
a) much greater than 1
b) slightly less than 1
c) equal to 1
d) slightly greater than 1

95. The self cleansing velocity for all sewers in India is usually
a) less than 1.0 m/sec
b) 1.0 m/sec to 1.2 m/sec
c) 1.5 m/sec to 2.0 m/sec
d) 3.0 m/sec to 3.5 m/sec

96. The slope of sewer shall be
a) given in the direction of natural slope of ground
b) given in the direction opposite to natural slope of ground
c) zero
d) steeper than 1 in 20
97. The design discharge for the separate sewer system shall be taken as
a) equal to dry weather flow (DWF)
b) 2xDWF
c) 3 x DWF
d) 6xDWF

98. The design discharge for the combined sewer system shall be taken as
a) equal to rainfall
b) rainfall + DWF
c) rainfall + 2 DWF
d) rainfall + 6 DWF

99. The minimum and maximum diameters of sewers shall preferably be
a) 15 cm and 100 cm
b) 15 cm and 300 cm
c) 30 cm and 450 cm
d) 60 cm and 300cm

100. The main disadvantage of cement concrete sewers is
a) less strength
b) difficulty in construction
c) difficulty in transportation due to heavy weight
d) less life

101. Most suitable section of sewer in separate sewage system is
a) rectangular section
b) circular section
c) standard form of egg shaped sewer
d) modified egg shaped section

102. An egg shaped section of sewer
a) is economical than circular section
b) provides self cleansing velocity at low discharges
c) is more stable than circular section
d) is easy to construct

103. The velocity of flow does not depend on
a) grade of sewer
b) length of sewer
c) hydraulic mean depth of sewer
d) roughness of sewer

104. The hydraulic mean depth (HMD) for an egg-shaped sewer flowing two-third full is
a) equal to HMD when flowing full
b) less than HMD when flowing full
c) greater than HMD when flowing full
d) none of the above

105. The effect of increasing diameter of sewer on the self cleansing velocity is
a) to decrease it
b) to increase it
c) fluctuating
d) nil

106. The most commonly used sewer under culverts is
a) circular brick sewer
b) circular cast iron sewer
c) semi-elliptical sewer
d) horse-shoe type sewer

107. The type of sewer which is suitable for both combined and separate system is
a) circular sewer
b) egg shaped sewer
c) horse-shoe type sewer
d) semi-elliptical sewer

108. The characteristics of fresh and septic sewage respectively are
a) acidic and alkaline
b) alkaline and acidic
c) both acidic
d) both alkaline

109. The pathogens can be killed by
a) nitrification
b) chlorination
c) oxidation
d) none of the above

110. Which of the following retards the self purification of stream ?
a) higher temperature
b) sunlight
c) satisfying oxygen demand
d) none of the above

111. Sewage treatment units are normally designed for
a) 5-10 years
b) 15-20 years
c) 30-40 years
d) 40-50 years

112. Settling velocity increases with
a) specific gravity of solid particles
b) size of particles
c) depth of tank
d) temperature of liquid

113. Standard BOD is measured at
a) 20°C – 1day
b) 25°C- 3day
c) 20°C – 5day
d) 30°C- 5day

114. The correct relation between theoretical oxygen demand (TOD), Biochemical oxygen demand (BOD) and Chemical
oxygen demand (COD) is given by

115. Select the correct statement.
a) 5 day BOD is the ultimate BOD.
b) 5 day BOD is greater than 4 day BOD keeping other conditions same.
c) 5 day BOD is less than 4 day BOD keeping other conditions same.
d) BOD does nof depend on time.

116. If Biochemical oxygen demand (BOD) of a town is 20000 kg/day and BOD per capita per day is 0.05 kg, then population equivalent of town is
a) 1000
b) 4000
c) 100000
d) 400000

117. The rate of BOD exerted at any time is
a) directly proportional to BOD satisfied
b) directly proportional to BOD remain-ing ,
c) inversely proportional to BOD satisfied
d) inversely proportional to BOD re-maining

118. The ratio of 5 day BOD to ultimate BOD is about
a) 1/3
b) 2/3
c) 3/4
d) 1.0

119. In a BOD test, 1.0 ml of raw sewage was diluted to 100 ml and the dissolved oxygen concentration of diluted sample at the beginning was 6 ppm and it was 4 ppm at the end of 5 day incubation at 20°C.
The BOD of raw sewage will be
a) 100 ppm
b) 200 ppm
c) 300 ppm
d) 400 ppm

120. The minimum dissolved oxygen which should always be present in water in order to save the aquatic life is
a) 1 ppm
b) 4 ppm
c) 10 ppm
d) 40 ppm

121. The relative stability of a sewage sample, whose dissolved oxygen is same as the total oxygen required to satisfy BOD, is
a) 1
b) 100
c) infinite
d) zero

122. Dissolved oxygen in streams is
a) maximum at noon
b) minimum at noon
c) maximum at midnight
d) same throughout the day

123. Facultative bacteria are able to work in
a) presence of oxygen only
b) absence of oxygen only
c) presence as well as in absence of oxygen
d) presence of water

124. The means of access for inspection and cleaning of sewer line is known as
a) inlet
b) manhole
c) drop manhole
d) catch basin

125. Sewerage system is designed for
a) maximum flow only
b) minimum flow only
c) average flow only
d) maximum and minimum flow

126. Sewage treatment units are designed for
a) maximum flow only
b) minimum flow only
c) average flow only
d) maximum and minimum flow

127. Laying of sewers is usually done with the help of
a) a theodolite
b) a compass
c) sight rails and boning rods
d) a plane table

128. Corrosion in concrete sewers is caused by
a) septic conditions
b) dissolved oxygen
c) chlorine
d) nitrogen

129. If the sewage contains grease and fatty oils, these are removed in
a) grit chambers
b) detritus tanks
c) skimming tanks
d) sedimentation tanks

130. Generally the detention period for grit chambers is kept as
a) 1 minute
b) 5 minutes
c) 2-4 hours
d) 12 hours

131. Which of the following unit works in anaerobic conditions?
a) sludge digestion tank
b) sedimentation tank
c) activated sludge treatment
d) trickling filters

132. Septic tank is a
i) settling tank
ii) digestion tank
iii) aeration tank
The correct answer is
a) only (i)
b) (i) and (ii)
c) (i) and (iii)
d) only (iii)

133. The maximum efficiency of BOD removal is achieved in
a) oxidation pond
b) oxidation ditch
c) aerated lagoons
d) trickling filters

134. The working conditions in imhoff tanks are
a) aerobic only
b) anaerobic only
c) aerobic in lower compartment and anaerobic in upper compartment
d) anaerobic in lower compartment and aerobic in upper compartment

135. In facultative stabilization pond, the sewage is treated by
a) aerobic bacteria only
b) algae only
c) dual action of aerobic bacteria and anaerobic bacteria
d) sedimentation

136. The detention period for oxidation ponds is usually kept as
a) 4-8 hours
b) 24 hours
c) 10 to 15 days
d) 3 months

137. Composting and lagooning are the methods of
a) sludge digestion
b) sludge disposal
c) sedimentation
d) filtration

138. The main disadvantage of oxidation pond is that
a) large area is required for construction
b) maintenance and operation cost are high
c) BOD removal is very low
d) none of the above

139. For satisfactory working of a sludge digestion unit, the pH range of digested sludge should be maintained as
a) 4.5 to 6.0
b) 6.5 to 8.0
c) 8.5 to 10.0
d) 10.5 to 12.0

140. Sludge volume index is defined as the ratio of
a) percentage of sludge by volume to percentage of suspended solids by weight
b) percentage of sludge by volume to percentage of total solids by weight
c) percentage of suspended solids by weight to percentage of sludge by volume
d) percentage of total solids by weight to percentage of sludge by volume

141. For normal sludge, the value of sludge index for Indian conditions is
a) 0 to 50
b) 50 to 150
c) 150 to 350
d) 350 to 500

142. When there is no recirculation of sewage, then recirculation factor is
a) 0
b) 1
c) infinity
d) none of the above

143. For the same solid content, if the quantity of sludge with moisture content of 98% is X, then the quantity of sludge with moisture content of 96% will be
a) X/4
b) X/2
c) X
d) 2X

144. A pipe which is installed in the house drainage to preserve the water seal of traps is called
a) vent pipe
b) antisiphonage pipe
c) waste pipe
d) soil pipe

145. In the two-pipe system of house plumbing, the pipes required are
a) one soil pipe, one waste pipe and one vent pipe
b) one soil pipe, two waste pipes and one vent pipe

146. The pipe which is used to carry the discharge from sanitary fittings like bath rooms, kitchens etc. is called
a) waste pipe
b) soil pipe
c) vent pipe
d) antisiphonage pipe

147. The gas from sludge digestion tank is mainly composed of
a) nitrogen
b) carbon dioxide
c) hydrogen sulphide
d) methane

148. Most of the bacteria in sewage are
a) parasitic
b) saprophytic
c) pathogenic
d) anaerobic

149. The process of lagooning is primarily a means of
a) reducing the excessive flow in sewers
b) disposing of sludge
c) increasing the capacity of storage re-servoirs
d) increasing flow of sewage through imhoff tanks

150. The biochemical treatment of sewage effluents is essentially a process of
a) oxidation
b) dehydration
c) reduction
d) alkalinization

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