Q.1
Percentage of bacterial load that can be removed from water by the process of plain sedimentation is about
  • 10 to 25
  • 50
  • 75
  • 100
Q.2
The type of sewer which is suitable for both combined and separate system is
  • Circular sewer
  • Egg shaped sewer
  • Horseshoe type sewer
  • Semi-elliptical sewer
Q.3
The dissolved oxygen level in natural unpolluted waters at normal temperature is found to be of the order of
  • 1 mg/liter
  • 10 mg/liter
  • 100 mg/liter
  • 1000 mg/liter
Q.4
The minimum dissolved oxygen which should always be present in water in order to save the aquatic life is
  • 1 ppm
  • 4 ppm
  • 10 ppm
  • 40 ppm
Q.5
The maximum permissible limit for fluoride in drinking water is
  • 0.1 mg/liter
  • 1.5 mg/liter
  • 5 mg/liter
  • 10 mg/liter
Q.6
Sludge volume index is defined as the ratio of
  • Percentage of sludge by volume to percentage of suspended solids by weight
  • Percentage of sludge by volume to percentage of total solids by weight
  • Percentage of suspended solids by weight to percentage of sludge by volume
  • Percentage of total solids by weight to percentage of sludge by volume
Q.7
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 filtersThe correct answer is
  • (i) and (ii)
  • (ii) and (iii)
  • (i) and (iv)
  • (ii) and (iv)
Q.8
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 waterThe correct answer is
  • (i) and (ii)
  • (i)and(iv)
  • (ii) and (iii)
  • (ii) and (iv)
Q.9
The amount of residual chlorine left in public water supply for safety against pathogenic bacteria is about
  • 0.01 to 0.05 ppm
  • 0.05 to 0.5 ppm
  • 0.5 to 1.0 ppm
  • 1.0 to 5.0 ppm
Q.10
Which of the following retards the self purification of stream?
  • Higher temperature
  • Sunlight
  • Satisfying oxygen demand
  • None of the above
Q.11
Sewage treatment units are normally designed for
  • 5 - 10 years
  • 15 - 20 years
  • 30 - 40 years
  • 40 - 50 years
Q.12
The polluted water is one which
  • Contains pathogenic bacteria
  • Consists of undesirable substances rendering it unfit for drinking and domestic use
  • Is safe and suitable for drinking and domestic use
  • Is contaminated
Q.13
Activated carbon is used for
  • Disinfection
  • Removing hardness
  • Removing odours
  • Removing corrosiveness
Q.14
Generally the detention period for grit chambers is kept as
  • 1 minute
  • 5 minutes
  • 24 hours
  • 12 hours
Q.15
In a BOD test, 1.0 ml of raw sewage was diluted toml 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
  • 100 ppm
  • 200 ppm
  • 300 ppm
  • 400 ppm
Q.16
Sewerage system is usually designed for
  • 10 years
  • 25 years
  • 50 years
  • 75 years
Q.17
The biochemical treatment of sewage effluents is essentially a process of
  • Oxidation
  • Dehydration
  • Reduction
  • Alkalinization
Q.18
The minimum and maximum diameters of sewers shall preferably be
  • 15 cm and 100 cm
  • 15 cm and 300 cm
  • 30 cm and 450 cm
  • 60 cm and 300 cm
0 h : 0 m : 1 s