81. Disinfection of water results in______________?
A. removal of turbidity
B. removal of hardness
C. killing of disease bacteria
D. complete sterilisation
✅ The correct answer is option C.
Environmental Engineering MCQs
82. The characteristics of fresh and septic sewage respectively are____________________?
A. acidic and alkaline
B. alkaline and acidic
C. both acidic
D. both alkaline
✅ The correct answer is option B.
83. 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)
✅ The correct answer is option C.
84. 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
✅ The correct answer is option C.
85. 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
✅ The correct answer is option B.
86. 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
✅ The correct answer is option C.
87. The chemical most commonly used to increase speed of sedimentation of sewage is_______________?
A. sulphuric acid
B. copper sulphate
C. lime
D. sodium permanganate
✅ The correct answer is option C.
88. The correct relation between theoretical oxygen demand (TOD), Biochemical oxygen demand (BOD) and Chemical oxygen demand (COD) is given by_______________?
A. TOD>BOD>COD
B. TOD>COD>BOD
C. BOD>COD>TOD
D. COD>BOD>TOD
✅ The correct answer is option B.
89. 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
✅ The correct answer is option C.
90. 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
✅ The correct answer is option C.