This set of Waste Water Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Lamella Clarifiers and Oil Removal belt”.
1. Lamella clarifier is also called as a inclined plate settler.
a) True
b) False
View Answer
Explanation: A lamella clarifier or inclined plate settler (IPS) is a type of settler designed to remove particulates from liquids. They are often employed in primary water treatment in place of conventional settling tanks.
2. Lamella clarifiers can also be used in mining industries.
a) True
b) False
View Answer
Explanation: Lamella clarifiers can be used in a range of industries including mining and metal finishing, as well as used to treat groundwater, industrial process water and backwash from sand filters.
3. __________ maintain the required water quality to the membrane without the use of chemicals.
a) Settlers
b) Primary settlers
c) Centrifugal tanks
d) Lamella settlers
View Answer
Explanation: Lamella clarifiers are able to maintain the required water quality to the membrane without the use of chemicals. The membranes do not work well with the large particles contained in flocculants and coagulants.
4. Lamella clarifiers are used as pre-treatment ahead of _____
a) PST
b) SST
c) Membrane filters
d) Centrifugal tanks
View Answer
Explanation: One specific application is as pre-treatment stage for effluent entering membrane filters. Lamella clarifiers are considered to be one of the best options for pre-treatment ahead of membrane filters.
5. What is the length of the tube in lamella clarifiers?
a) 0.5-1 m
b) 1-2 m
c) 2-3 m
d) 3-5 m
View Answer
Explanation: The length of lamella clarifiers is 1-2 m with a plate or tube spacing of 50 mm. The minimum plate pitch is 7˚ and the typical loading rate is 5-10 m/h.
6. How much spacing should be provided in between the tubes?
a) 10 mm
b) 20 mm
c) 30 mm
d) 50 mm
View Answer
Explanation: The minimum plate pitch is 7˚ and the typical loading rate is 5-10 m/h. The length of lamella clarifiers is 1-2 m with a plate or tube spacing of 50 mm.
7. What is the maximum load of solids that lamella clarifiers can handle?
a) 1000 mg/L
b) 2000 mg/L
c) 3000 mg/L
d) 4000 mg/L
View Answer
Explanation: A maximum feed water concentration of 1000 mg/L of grease and 3000 mg/L of solids can be handled by lamella clarifiers. Treated water has a turbidity of around 1-2 NTU.
8. What is the retention time for rectangular clarifiers?
a) 1-2 h
b) 2-3 h
c) 3-6 h
d) 6-8 h
View Answer
Explanation: The retention time for rectangular clarifiers is 2-3 hours, for circular clarifiers, it is 1-2 hours and for lamella clarifiers, it is 1-2 hours.
9. What is the range of overflow rate for circular clarification unit?
a) 1-3 m3/m2/h
b) 2-8 m3/m2/h
c) 3-10 m3/m2/h
d) 5-12 m3/m2/h
View Answer
Explanation: The overflow rate for circular clarification unit is 1-3 m3/m2/h, for rectangular clarification unit it is 1-2 m3/m2/h and for lamella clarifiers, it is 5-12 m3/m2/h.
10. What is the retention time for lamella clarifiers?
a) 1-2 h
b) 2-4 h
c) 4-6 h
d) 6-8 h
View Answer
Explanation: The retention time for circular and lamella clarifiers is 1-2 hours and the retention time for rectangular clarifiers and floc blanket is 2-3 hours.
11. What is the limit of plate load?
a) 10.7 m/h
b) 8.2 m/h
c) 5.4 m/h
d) 2.9 m/h
View Answer
Explanation: Loadings on plates should be limited to 2.9 m/h to ensure laminar flow is maintained between plates. Rise rates can be between 0.8 and 4.88 m/h.
12. What is the angle of inclination for lamella plates?
a) 20-30˚
b) 30-40˚
c) 40-60˚
d) 50-70˚
View Answer
Explanation: The general consensus is that plates should be inclined at a 50-70° angle from the horizontal to allow for self-cleaning. The projected plate area of the lamella clarifier takes up approximately 50% of the space of a conventional clarifier.
13. Which of these pollutants does a lamella clarifier remove?
a) TSS
b) BOD
c) TDS
d) Odour
View Answer
Explanation: Lamella clarifier majorly is used to remove TSS. This has plates arranged parallelly. These plates may be made up of PVC.
14. What is the maximum rise rate in m3/m2/h considered while designing a Lamella clarifier?
a) 1
b) 2
c) 1.2
d) 1.5
View Answer
Explanation: Based on the rise rate,the area of the lamella clarifier is arrived. This is assumed as 1.2 m3/m2/h. The minimum rise rate considered is 0.6 m3/m2/h.
15. Calculate the flow per plate in a lamella clarifier for the following data?
Flow: 20m3/h
Area of plate: 1.2 m2
Rise rate: 1.2 m3/m2/h
a) 1.44 m3/h
b) 1.55 m3/h
c) 1.66 m3/h
d) 1.04 m3/h
View Answer
Explanation: The flow per plate is calculated as rise rate multiplied by area per plate. This is used in the calculation to calculate the total number of plates required .Flow per plate = 1.2 m3/m2/h x 1.2m/h = 1.44 m3/h.
16. How many plates will be required in a lamella clarifier for the following data?
Flow: 40m3/h
Area of plate: 1.2 m2
Rise rate: 1.2 m3/m2/h
a) 27
b) 25
c) 29
d) 30
View Answer
Explanation: The flow per plate is calculated as rise rate multiplied by area per plate. Then the total flow is divided by flow per plate. The answer obtained equals to the number of plate required. In this case no: of plates = 40/ (1.2 m3/m2/h x 1.2 m2)=29.
17. What is the angle at which the plates should be inclined in a lamella clarifier?
a) 70-80 degree
b) 45-60 degree
c) 20-35 degree
d) 35-45 degree
View Answer
Explanation: The plates in an inclined lamella clarifier are inclined at 45-60 degree. This was first described by Hazen. Hazen introduced this system in the year 1904.
18. How many plates will be required in a lamella clarifier for the following data?
Flow: 120m3/h
Area of plate: 1.8m2
Rise rate: 0.9 m3/m2/h
a) 75
b) 80
c) 85
d) 90
View Answer
Explanation: The flow per plate is calculated as rise rate multiplied by per area of the plate. Then the total flow is divided by flow per plate. The answer obtained equals to the number of plate required. In this case no: of plates = 120/ (0.9 m3/m2/h x 1.8 m2)=75
19. Calculate the Oil load for the following data.
Flow rate: 1000 m3/day
Oil present: 50 ppm
a) 2.08 Kg/h
b) 1.36 Kg/h
c) 1.48 Kg/h
d) 2.52 Kg/h
View Answer
Explanation: The oil load is calculated as Flow rate x oil present. It is expressed as Kg/h. The oil load is expressed as Flow rate x oil present = 1000 x 50 / (24*1000) = 2.08 Kg/h.
20. What is the capacity of the oil skimmer used?
Flow: 90m3/h
Oil present: 50 ppm
a) 5 LPH
b) 15 LPH
c) 18 LPH
d) 8 LPH
View Answer
Explanation: The oil load is calculated as Flow rate x oil present. It is expressed as Kg/h. The oil load is expressed as Flow rate x oil present = 90 x 50 / 1000= 4.5 Kg/h. The density of oil = 0.9 gm/cc. Therefore the oil skimmer required is 4.5/0.9 = 5 LPH.
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