Waste Water Engineering Questions and Answers - Unit Operations and Unit Processes Part-1

1. _________ is simply detaining water for a sufficient time.
a) Coagulation
b) Flocculation
c) Sedimentation
d) Filtration

Answer: c
Explanation: Sedimentation is simply detaining water for a sufficient time mostly in stagnant or relatively stagnant position to make the flow velocity of water less than the settling velocity of the solid particles that they without being driven by horizontal force settles down by gravity.

2. What is the removal of fine particle sand dissolved solids called?
a) Filtration
b) Sedimentation
c) Deoxidation
d) Disinfection

Answer: a
Explanation: Filtration is to the removal of fine particle sand dissolved solids where the fine sand layer and coarse sand layer below serves as the media to remove colloidal solids and the water remains completely free of solids

3. How are colour and odour removed?
a) Adsorption
b) Sedimentation
c) Filtration
d) Coagulation

Answer: a
Explanation: Odour and colour present in water and waste water are removed by aeration and adsorption process. The odour and colour causing elements are adsorbed and aerated that the water is free from impurities for use and wastewater for reuse and recycling.

4. The law of ________ states that mass can neither be created nor destroyed.
a) Radiation
b) Wastewater
c) Conversion of mass
d) Water

Answer: c
Explanation: The law of conservation of mass states that mass can neither be created nor destroyed. Thus in a processing plant, the total mass of material entering the plant must equal the total mass of material leaving the plant, less any accumulation left in the plant.

5. What is the size of openings of a coarse screen?
a) 6mm-150mm
b) 150-200mm
c) >200mm
d) < 6mm

Answer: a
Explanation: The size of the coarse screens ranges from 6-150mm. Coarse screens are further classified as hand cleaned and mechanically cleaned. Coarse screens remove large particles and prevent clogging in pipes and pumps.

6. While designing a mechanical screen, the clear space between the bars would be in what range?
a) 15-75mm
b) 25-50mm
c) 20-40mm
d) >75mm

Answer: a
Explanation: The clear space between the bars for a mechanical screen would be in the range 15-75mm. The clear space between the bars for a hand screen would be 25-50mm. The slope from the vertical for these screens would range from 0-30 degree

7. What is the maximum approach velocity to be considered for a mechanical screen while designing it?
a) 0.3-0.5m/s
b) 0.6-1m/s
c) 1-1.5m/s
d) 2 m/s

Answer: b
Explanation: The maximum approach velocity for a mechanical screen would be in the range 0.6-1m/s. The minimum approach velocity would be in the range 0.3-0.5m/s. These mechanical screens reduce manual labour.

8. What is the size of the openings for a fine screen?
a) 0.1 mm
b) 0.8-1mm
c) 0.2-0.6mm
d) 1-3mm

Answer: c
Explanation: The size of openings for a fine screen is 0.2-0.6mm. These are used as a substitute for a primary clarifier. These are used to remove the suspended particles.

9. What is the percentage of TSS removed by a rotary drum fine screen?
a) 50%
b) 60%
c) 65-75%
d) 25-45%

Answer: d
Explanation: 25-45 percentage of TSS is removed by rotary drum fine screens. This however actually depends on the nature of the waste water. Also it depends on the waste water travel time.

10. Which type of mixers are used to mix coagulants like alum, ferric ammonium sulphate and coagulant aids such as polyelectrolyte and lime?
a) Static mixers
b) Mechanical mixers
c) Mechanical aerators
d) Paddle mixers

Answer: d
Explanation: Paddle mixers are used to mix coagulants and coagulant aids. Paddle flocculators contain appropriately spaced paddles mounted on a shaft. Flocculation is brought about by the movement of the slow moving paddles.