Category: WASTE WATER Engineering Objective Questions

250+ TOP MCQs on Rapid Filtration and Answers

Waste Water Engineering Multiple Choice Questions on “Rapid Filtration”.

1. When was the rapid sand filer first used?
a) 1930
b) 1920
c) 1950
d) 1960
Answer: b
Clarification: The first modern rapid sand filtration plant was designed and built by George W. Fuller in Little Falls, New Jersey. Fuller’s filtration plant went into operation in 1920 and its success was responsible for the change to this technology in the U.S.

2. Rapid sand filters require large area compared to slow sand filters.
a) True
b) False
Answer: b
Clarification: Rapid sand filters were widely used in large municipal water systems by the 1920s because they required smaller land areas compared to slow sand filters.

3. Pressure flow is considered in rapid filtration.
a) True
b) False
Answer: b
Clarification: The polluted or unfiltered water flows through the filter medium under gravity or under pumped pressure and the floc material is trapped in the sand matrix.

4. Which of the following processes is not done before rapid filtration?
a) Mixing
b) Flocculation
c) Sedimentation
d) Chlorination
Answer: d
Clarification: Mixing, flocculation and sedimentation processes are typical treatment stages that precede filtration. Chemical additives, such as coagulants are often used in conjunction with the filtration system.

5. The direction of water in filter beds is reversed for ______
a) Filtration
b) Cleaning
c) Decreasing velocity
d) Decreasing flow
Answer: b
Clarification: Rapid sand filters must be cleaned frequently, often several times a day, by backwashing, which involves reversing the direction of the water and adding compressed air.

6. For a rapid sand filter, what is the ratio of length: breadth while designing it?
a) 1:2
b) 1:3
c) 2:3
d) 4:1
Answer: b
Clarification: For a rapid sand filter the ratio of length: breadth while designing it is 1:3. The area is calculated from the velocity and the flowrate of water. From this ratio and the area, the length and breadth of the filter are calculated.

7. Calculate the area of the rapid sand filter for the following details.
Flow: 2000 m3/h.
Velocity: 5m/h
Backwash time: 30 mins
a) 18 m2
b) 20 m2
c) 22 m2
d) 16 m2
Answer: a
Clarification: The total operation time equals 24 minus the back wash time. Area equals Flowrate × total hours of operation/ [velocity × total hours of operation × (total hours of operation-backwash time). Area= 2000 × 24/ (5 × 24 × 23.5) =18 m2.

8. Calculate the length of the rapid sand filter for the following details.
Flow: 1000 m3/h.
Velocity: 5m/h
Backwash time: 30 mins
a) 1.0 m
b) 1.9 m
c) 1.7 m
d) 1.2 m
Answer: b
Clarification: The total operation time equals 24 minus the back wash time. Area equals Flowrate × total hours of operation/ [velocity × total hours of operation × (total hours of operation-backwash time). Area= 1000 × 24/ (5 × 24 × 23.5) =9 m2. Length: Breadth is in the ratio 1:3. Length = 1.7 m.

9. Calculate the breadth of the rapid sand filter for the following details.
Flow: 500 m3/h.
Velocity: 5 m/h
Backwash time: 20 mins
a) 4.5 m
b) 5.7 m
c) 3.7 m
d) 7.5 m
Answer: c
Clarification: The total operation time equals 24 minus the back wash time. Area equals Flowrate × total hours of operation/ [velocity × total hours of operation × (total hours of operation-backwash time). Area= 500 × 24/ (5 × 24 × 23.7) =4.5 m2. Length: Breadth is in the ratio 1:3. Breadth = 3.7 m.

10. What is the turbidity achieved by using a rapid filtration system?
a) 0.1 NTU
b) 0.7 NTU
c) 1.5 NTU
d) 0.9 NTU
Answer: a
Clarification: The turbidity achieved by using a rapid filtration system is 0.1 NTU. This is used to operate systems which have rates greater than 100 times that of slow sand filtration. Coagulation is used to precondition the water.

11. What is the limit of turbidity which a 2 stage filtration a handle?
a) 180 NTU
b) <100 NTU
c) 50 NTU
d) 200 NTU
Answer: b
Clarification: Two stage filtration is a type of Rapid filtration. This can handle upto 100 NTU. This is followed by a rough filter after a coagulation system. The rough filter is followed by a filtration system.

12. What is the height of the anthracite maintained in a dual media filter?
a) 1.5-1.8 m
b) 2.2 -2.4 m
c) 2.5-2.8 m
d) 2.8-3.0 m
Answer: a
Clarification: The height of the anthracite maintained in dual media filter is 1.5-1.8 m. Initially, the height maintained used to be 0.45-0.6 m. GAC is sometimes used instead of anthracite in case of dual media filters.

13. What is the height maintained of a deep bed monomedia?
a) 1.5-1.8 m
b) 2.2 -2.4 m
c) 2.5-2.8 m
d) 2.8-3.0 m
Answer: a
Clarification: The height of the deep bed monomedia is maintained at 1.5-1.8 m. This is a type of rapid filtration. The media is usually GAC/Anthracite.

250+ TOP MCQs on Reverse Osmosis Design and Answers

Waste Water Engineering Multiple Choice Questions on “Reverse Osmosis Design”.

1. The ________ the salt rejection, the better the system is performing.
a) Higher
b) Lower
c) Moderate
d) Poor
Answer: a
Clarification: The higher the salt rejection, the better the system is performing. A low salt rejection can mean that the membranes require cleaning or replacement.

2. What is the osmotic pressure for sea water?
a) 1.5 Mpa
b) 1.8 Mpa
c) 2.3 Mpa
d) 2.45 Mpa
Answer: d
Clarification: The osmotic pressure of sea water is 2.45 Mpa. The concentration of salt in sea water is 32000-35000 mg/l. The applied pressure on the RO equipment is 5.6-6.

3. Membrane permeation rate increases proportionally to effective pressure.
a) True
b) False
Answer: a
Clarification: Although membrane permeation rate increases proportionally to effective pressure, the highest recommended applied pressure of commercial membranes presently available is 7.0 Mpa.

4. RO membranes are made of _______
a) Plastic
b) Cotton
c) Silk
d) Polymer
Answer: d
Clarification: The highest recommended applied pressure of commercial membranes presently available is 7.0 Mpa; beyond which compaction will start to occur due to the fact that RO membranes are made of polymers.

5. Concentrated seawater which is called _________
a) Permeate
b) Brine
c) RO water
d) Salt water
Answer: b
Clarification: When fresh water is separated from seawater, concentrated seawater which is called brine and is retained on the surface of the RO membrane.

6. The osmotic pressure of the brine increases proportionally to the salt concentration.
a) True
b) False
Answer: a
Clarification: The salt concentration and the osmotic pressure of the brine are related proportionally, i.e., the osmotic pressure of the brine increases as the salt concentration increases.

7. The upper limit of brine concentration is ______ times the normal sea water.
a) 1.5
b) 2
c) 2.5
d) 3
Answer: c
Clarification: The upper limit of the brine concentration is usually fixed. The upper limit is normally 1.6-2.5 times that of the normal seawater.

8. The water flux of RO membranes ______ as water viscosity lowers.
a) Increases
b) Decreases
c) Alters
d) Fluctuates
Answer: a
Clarification: When the water viscosity is lowered, the water flux of RO membranes increases and the water viscosity is lowered by an increase in temperature. Thus, the higher the temperature better is the flux.

9. What is the maximum acceptable limit of temperature for RO?
a) 20˚C
b) 30˚C
c) 40˚C
d) 50˚C
Answer: c
Clarification: In order to reduce the effects of temperature to a minimum, the acceptable upper limit is 40°C. RO systems operate at 25°C usually.

10. What is the design temperature of RO systems?
a) 20˚C
b) 25˚C
c) 30˚C
d) 35˚C
Answer: b
Clarification: RO systems are usually designed to operate at 25°C and water flux falls by 20–25 percent when water temperature is lowered by 10°C.

11. What is the operating pH for RO systems?
a) 2-3
b) 4-6
c) 5-7
d) 8-9
Answer: c
Clarification: The pH of seawater is 8–8.5 in general. The pH is reduced to 5-7 in order to reduce scaling on the surface and chemical deterioration of the RO membrane.

12. Calculate the number of membranes required for the following data:
Flow: 535 m3/h.
Area: 400 m2
Flux considered: 12 lmh
a) 112
b) 115
c) 117
d) 120
Answer: a
Clarification: Number of membranes is calculated based on the flow and area. Flux is generally fixed based on the TDS present in the raw water. Number of membranes = Flow x 1000/flux/area. A number of membranes = 535/400/12=112.

13. Calculate the recovery for the following data:
Product Flow: 535 m3/h.
Feed flow : 635 m3/h.
Flux considered: 12 lmh
a) 80%
b) 85%
c) 90%
d) 75%
Answer: b
Clarification: Recovery= Feed flow/Permeate flow. In this case recovery is 85%. This is arrived by 535/635*100=85%.

14. What is the thumb rule to consider for osmotic pressure?
a) 1 psi for every 86 ppm of Na
b) 2 psi for every 86ppm of Na
c) 1 psi for every 43 ppm of Na
d) 2 psi for every 43 ppm of Na
Answer: a
Clarification: The tendency of a pure solution constituting low solute concentration to flow into solution constituting higher solute concentration is known as osmosis. When pressure greater than osmotic pressure is applied then reverse osmosis takes place. The thumb rule for the consideration of osmotic pressure is 1 psi for every 86 ppm of Na.

15. What is the flux considered while designing a reverse osmosis system for treating RO permeate?
a) 30-40 LMH
b) 12-18 LMH
c) 20-25 LMH
d) 25-30 LMH
Answer: a
Clarification: Flux is the amount of water flowing through a particular area. This is dependent both on the nature of water and the membrane surface area. The flux considered for RO permeate is 30-40 LMH.

16. What is the flux considered while designing a reverse osmosis system for treating bore well water?
a) 30-40 LMH
b) 40-50 LMH
c) 20-30 LMH
d) 12-18 LMH
Answer: c
Clarification: The flux increases with increase in pressure. It also increases with increase in temperature. In case of bore well water, the flux considered is 20-30 LMH.

17. What is the flux considered while designing a reverse osmosis system for treating surface water?
a) 15-22 LMH
b) 22-30 LMH
c) 12-15 LMH
d) 30-35 LMH
Answer: a
Clarification: The flux to be considered depends on the nature of the water to be treated. The flux is used to determine the number of membranes required for the treatment system. In the case of treating surface water by a conventional method the flux to be considered is 15-22 LMH.

18. What is the flux considered while designing a reverse osmosis system for treating surface water with UF system?
a) 15-20 LMH
b) 20-30 LMH
c) 12-15 LMH
d) 30-35 LMH
Answer: b
Clarification: The flux to treat surface water by a conventional method and to treat by UF differs. Conventional method includes Dual media filters. In case the surface water is treated by conventional, the flux considered should be around 20-30 LMH.

19. How is Net driving pressure mathematically expressed?
a) Net driving pressure = Pf – 0.5 * DP – Pp -Posmavg
b) Net driving pressure = 0.5 * DP –Pp – Posmavg
c) Net driving pressure = Pf – 0.5 * DP – Pp
d) Net driving pressure = Pf * DP – Pp -Posmavg
Answer: a
Clarification: Net driving pressure = Pf – 0.5 * DP – Pp -Posmavg. The net driving pressure is the pressure required to adequately sustain osmotic pressure. Here Pf is the feed pressure. DP is the pressure drop and Pp is the Permeate pressure.

250+ TOP MCQs on Principles of House Drainage and Answers

Waste Water Engineering Multiple Choice Questions on “Principles of House Drainage”.

1. The sewers should be laid ______
a) Below the building
b) Side of the building
c) Within the building
d) Across the building

Answer: b
Clarification: It is advisable to lay sewers by the side of the building rather than below the building. The drains should be laid at an angle of 180˚ between the inspection manholes.

2. What is the angle between the drains and inspection manholes?
a) 45˚
b) 90˚
c) 135˚
d) 180˚

Answer: d
Clarification: The drains should be laid at an angle of 180˚ between the inspection manholes. Drains from different houses should be connected to public sewers only if the level permits.

3. The entire system should be ventilation free.
a) True
b) False

Answer: b
Clarification: The entire sewer system should have proper ventilation. The house drainage should be containing enough number of traps at suitable points for the efficient functioning of it. The joints should be watertight.

4. _________ is the removal of excess surface water from the land to enhance crop growth.
a) Sewer drainage
b) Agricultural drainage
c) Municipal drainage
d) Soil drainage

Answer: b
Clarification: Agricultural land drainage is the removal of excess surface and subsurface water from the land to enhance crop growth, including the removal of soluble salts from the soil.

5. Which of the following is not correct with respect to installing the drainage system in the waterlogged land?
a) Increase in water amount in soil
b) Reduction in water amount on soil
c) Discharge of water through the system
d) Reducing waterlogging

Answer: a
Clarification: The direct effects of installing a drainage system in the waterlogged land are the reduction in the average amount of water in the soil mass and on the surface soil inducing drier soil conditions.

6. Which of these is negative effect owing to the drier soil conditions?
a) Aeration of soil
b) Soil structure
c) Availability of nitrogen
d) Irrigation efficiency

Answer: d
Clarification: Aeration of the soil increases with improved soil structure and availability of the nitrogen. Irrigation efficiency is negative.

7. Which of these is a positive effect owing to the drier soil conditions?
a) Irrigation efficiency
b) Risk of drought
c) Organic matter
d) Crop production

Answer: d
Clarification: The positive effects are increased aeration of the soil, stabilized soil structure, higher availability of nitrogen in the soil, higher and more diversified crop production and better workability of the land.

8. Which of these is a positive effect owing to the discharge?
a) Leaching of nutrients
b) Environmental damage
c) Interference with infrastructural elements of land
d) Removal of salts

Answer: d
Clarification: Positive effects owing to the discharge are the removal of salts or other harmful substances from the soil, availability of drainage water for various purposes.

9. What is the time required for the depletion of oxygen in soil by waterlogging?
a) 6-12 hours
b) 1-2 days
c) 3-6 days
d) 1-4 weeks

Answer: b
Clarification: The adverse effects of drainage may be broadly classified as impaired crop growth, formation of water logged soils waterlogging- causes oxygen deficits in soils, usually within 1-2 days.

10. What is the average land coverage of vertisols in Ethiopia?
a) 5 million ha
b) 10 million ha
c) 13 million ha
d) 16 million ha

Answer: c
Clarification: Vertisols (deep black clay soils) cover about 13 million ha in Ethiopia. The highland Vertisols above 1500 m altitude cover 7.6 million ha, of which 1.93 million ha are currently cropped (about 23% of all Ethiopian crop land).

11. What is the power of diminishment of van der Waals force with respect to distance?
a) 2
b) 4
c) 6
d) 8

Answer: c
Clarification: Water molecules are attracted to solid surfaces by various types of London-van der Waals forces. These are strong, but very short-range forces; they diminish with about the sixth power of the distance.

250+ TOP MCQs on Pumps & Pumping Stations – 2 and Answers

Waste Water Engineering Interview Questions and Answers on “Pumps & Pumping Stations – 2”.

1. Pumping stations are necessary where pressures have to be decreased.
a) True
b) False
Answer: b
Clarification: Pumping stations are necessary where water is pumped directly into system o where pressure has to be increased because there is an insufficient difference in water levels in gravity flow distribution systems.

2. The most expensive part is the energy supply for pumps.
a) True
b) False
Answer: a
Clarification: Pumping stations are situated where water has to be pumped into a distribution system or where pressure levels are to be increased. This requires high energy supplies and is expensive.

3. To reduce the expenses, the pumps must have a high degree of ________
a) Flow rate
b) Efficiency
c) Power
d) Intake
Answer: b
Clarification: To reduce the expenses, the pumps must have a high degree of efficiency and must be maintained properly. To guarantee safe water quality, cross connection of drinking water and waste removal systems must be avoided.

4. What are the facilities including pumps and other equipment for pumping fluids from one place to another called?
a) Pumping facilities
b) Pumping stations
c) Pumping house
d) Pump and equipment facilities
Answer: b
Clarification: Pumping stations are used for a variety of infrastructures such as the supply of water to canals, the drainage of low-lying land and the removal of sewage to processing sites.

5. What is a building where the pumps are located and operated called?
a) Pumping station
b) Pump house
c) Pumping facility
d) Pumping house
Answer: b
Clarification: A building where the pumps are located and operated is called a pump house. This consists of pumps of an irrigation system with a pressurized water filtration system.

6. In duplex pump stations, the pumps shall be of __________
a) Same pressure
b) Same efficiency
c) Same capacity
d) Different capacity
Answer: c
Clarification: In duplex pump stations, the pumps shall be of the same capacity. If pumps are in series it is required to meet the capacity of total dynamic head requirement, each set of pumps in series shall be viewed as a single pumping unit.

7. The road way to the pumping station must be a _______
a) Hard surface
b) Muddy road
c) Hilly road
d) Smoother path
Answer: a
Clarification: The road way to the pumping station must be an all-weather roadway. The road way must be provided on a hard surface. Muddy roads lead to inconvenience during the rainy season.

8. In a desalination plant in order to provide high pressure greater than the osmotic pressure which type of pump is selected?
a) Reciprocating Pump
b) Positive Displacement Pump
c) Booster Pump
d) Multistage Pump
Answer: d
Clarification: Multistage Pumps have two/more impellers and a corresponding number of volute cases. Since there are multiple volute cases the pressure obtained is more than that obtained by a single stage pump. However, the volume of the fluid handled remains constant in both the cases.

9. Generally, what is the Material of Construction of the casing of the pumps which are used in a desalination plant?
a) Cast Iron
b) Bronze
c) Stainless Steel SS 304 GRADE
d) Stainless Steel SS 316 L Grade
Answer: d
Clarification: The inlet water of any desalination plant would have a minimum TDS of 25,000 ppm. Since this water has high concentration of ions it can easily corrode the inner parts of the pump. Hence the quality of Steel of 316 L is preferred.

10. Which type of pump is used when chemicals are to be dosed in water treatment plant?
a) Plunger Pump
b) Positive Displacement Pump
c) Vertical Turbine Pump
d) Jet Pump
Answer: b
Clarification: Positive Displacement Pump is used to pump liquids with high viscosity. These are also known as a reciprocating pump. These pumps are used when the fluid to be pumped is at low flow and high pressure.

11. Which is the part of the pump which prevents the flow of water from the volume to enter back to the impeller?
a) Shaft
b) Bearing
c) Mechanical seal
d) Wear rings
Answer: d
Clarification: Water from the high pressure zone of the volute could re-enter the impeller. In order to prevent this a physical separation between the high and low pressure side is provided. Wear ring provides a flow restriction in order to prevent the water from entering the impeller again.

12. For a mechanical seal which is the normal leakage rate?
a) 30-50 drops of seal water/min
b) 40-60 drops of seal water/min
c) 20-40 drops of seal water/min
d) 20-60 drops of seal water/min
Answer: d
Clarification: A normal leakage rate is 20-60 drops of seal water/min. If it is below 20 drops of seal water/min then the operator should gradually loosen the packing gland nuts. He should observe the leakage rate after loosening the gland.

13. In order to reduce the operation and maintenance which of the following characteristics of a pump should be considered?
a) Efficiency of the pump
b) Flow rate
c) NPSH
d) Head
Answer: a
Clarification: Higher the efficiency of the pump lesser will be the power consumed. Hence the electricity consumed by the pump would be low. This will result in a lesser maintenance cost of the pump.

14. Which type of impeller is usually preferred when handling liquids with solids?
a) Closed impeller
b) Open impeller
c) Single suction impeller
d) Double suction impeller
Answer: b
Clarification: Open impellers are used to handle water with a large concentration of solid. Also open impellers get damaged more than the closed impellers as the vanes are exposed directly. These impellers usually handle water which is at a low pressure.

15. Which type of pump is used when the effluent should be pumped back into the plant for use as service water?
a) Vortex Pump
b) Vertical Turbine Pump
c) Sump pump
d) Rotary pump
Answer: b
Clarification: The construction of the turbine pumps enables to handle clean water. Line shaft turbine pump has been used t0 draw water from deep wells. In case the effluent has to be pumped back as service water then Vertical Turbine pumps are apt for the same application.

16. Which formula is used to calculate the head for centrifugal pumps?
a) H=P(PSIG)X144/Specific gravity
b) H=P(PSIG)X2.31/Specific gravity
c) H=P(ft)X144/Specific gravity
d) H=P(ft)X2.31/Specific gravity
Answer: b
Clarification: As pressure increases head too increases. Similarly sp. Gravity is inversely proportional. This formula holds good when the head is measured at psig.

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250+ TOP MCQs on Methods for Treatment of Wastewater – 2 and Answers

Waste Water Engineering Question Paper on “Methods for Treatment of Wastewater – 2”.

1. What is the method of treatment used when the TSS in the sample is high?
a) Ultrafiltration
b) High rate solid contact clarifier
c) Pressure Sand filter
d) Activated Carbon filter
Answer: b
Clarification: High rate solid contact clarifier is used to treat samples with very high TSS. The other methods namely ultrafiltration and pressure sand filter cannot treat samples with very high TSS. This is because the filters will get clogged.

2. Which type of treatment does clarification fall in?
a) Secondary treatment
b) Primary treatment
c) Preliminary treatment
d) Tertiary treatment
Answer: b
Clarification: Clarification is classified as Primary treatment. Influent with high TSS can be treated here. The COD associated TSS also gets reduced in this stage.

3. Which of these remove coarse materials?
a) Coarse screen
b) Grit chamber
c) Fine screen
d) Commutors
Answer: a
Clarification: Coarse screens remove coarse materials. The size of the coarse screen is 6mm-25mm. These coarse screens maybe manual or mechanically driven.

4. Which type of treatment is the coarse screen?
a) Preliminary treatment
b) Primary treatment
c) Secondary treatment
d) Tertiary treatment
Answer: a
Clarification: Coarse screens are classified as preliminary treatment. This is mainly to remove grit, sand particles. This prevents clogging of the pipe and pump.

5. Tube settlers are classified as which type of treatment?
a) Tertiary treatment
b) Secondary treatment
c) Preliminary treatment
d) Primary treatment
Answer: b
Clarification: Tube settlers are classified as secondary treatment. These are used mainly to remove TSS. Tube settlers will be followed generally after a clarifier and a flocculator.

6. Activated Carbon is classified as which type of treatment?
a) Preliminary treatment
b) Primary treatment
c) Secondary treatment
d) Tertiary treatment
Answer: d
Clarification: Activated Carbon is classified as tertiary treatment. This works on the principle of adsorption. Pressure sand filter is usually prior to the activated carbon filter.

7. Which of these is used to remove odour?
a) Ultrafiltration
b) Pressure sand filter
c) Activated carbon
d) Nano filter
Answer: c
Clarification: Activated carbon filters are used to remove odour. This is also used to reduce COD by removing organics. The treatment process works on the principal of adsorption.

8. Reverse Osmosis is which type of treatment?
a) Primary treatment
b) Preliminary treatment
c) Secondary treatment
d) Tertiary treatment
Answer: d
Clarification: Reverse Osmosis is classified as tertiary treatment. This is mainly used to remove ions. This results in the reduction of total dissolved salts.

9. Which is usually prior to reverse osmosis?
a) Ultrafiltration
b) Activated carbon filter
c) Clarifier
d) Tube settler
Answer: a
Clarification: Ultrafiltration is usually prior to reverse osmosis. This is to remove the TSS present in the sample. Reverse osmosis reduces the total dissolved solids in the water sample.

10. What does zero discharge actually refer to?
a) There is zero discharge of ions
b) The reject is recycled from every part of the treatment plant
c) The reject is not rejected out. Influent equals effluent
d) 100 percent efficient plant
Answer: b
Clarification: Zero discharge usually refers to the treatment plant in which the reject from each part of the treatment plant is recycled. The reject is fed as the influent and once again treated. The removal efficiency of the pollutants is approximately 97-98%.

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250+ TOP MCQs on Trickling Filters – 1 and Answers

Waste Water Engineering Multiple Choice Questions on “Trickling Filters – 1”.

1. Who used the trickling filter for the first time?
a) Didden
b) Streeter
c) Thomas
d) Newton
Answer: a
Clarification: Trickling filter consists of a fixed bed of rocks, lava, coke, gravel and polyurethane over which sewage or other wastewater flows downward and causes a layer of microbial slime. It was first used by Didden.

2. Splashing helps in improving aerobic conditions.
a) True
b) False
Answer: a
Clarification: Splashing, diffusion, etc. increases aerobic conditions and it is increased either by forced-air flowing through the bed or natural convection of air if the filter medium is porous.

3. Trickling filter can also be called as a biofilter.
a) True
b) False
Answer: a
Clarification: The systems like trickling filter and biofilter have also been described as roughing filters, intermittent filters, packed media bed filters, alternative septic systems, percolating filters, attached growth processes, and fixed film processes.

4. The supernatant from the tank flows into a ____
a) Trickling filter
b) Dosing device
c) Pumping station
d) Sedimentation tank
Answer: b
Clarification: The supernatant from the tank flows into a dosing device, often a tipping bucket which delivers flow to the arms of the filter. The flush of water flows through the arms and exits through a series of holes pointing at an angle downwards.

5. __________ in trickling filter contains many species like bacteria and round worms.
a) Treated water
b) Wastewater
c) Biofilm
d) Air influent
Answer: c
Clarification: The bio-film that develops in a trickling filter may become several millimeters thick and is typically a gelatinous matrix that contains many species of bacteria, ciliates and amoeboid protozoa, annelids, round worms and insect larvae and many other micro fauna.

6. Which of the following is not used as a media for trickling filters?
a) Sand
b) Geotextiles
c) Gravel
d) Paper
Answer: d
Clarification: Trickling may have a variety of types of filter media used to support the biofilm. Coke, pumice, plastic matrix material, open-cell polyurethane foam, clinker, gravel, sand and geotextiles are the most common type of media used.

7. Which of the following causes thickening of the biofilm?
a) Reduction of intake wastewater
b) Rapid growth of organisms
c) Reduction in air supply
d) Increase in acidity
Answer: b
Clarification: At certain times of the year, especially in the spring, rapid growth of organisms in the film may cause the film to be too thick and it may slough off in patches leading to the “spring slough”.

8. What is the shape of a typical trickling filter?
a) Circular
b) Cylindrical
c) Square
d) Rectangular
Answer: a
Clarification: A typical trickling filter is circular and between 10 meters and 20 meters across and between 2 meters to 3 meters deep. A wall, circular, often of brick, contains a bed of filter media which in turn rests on a base of under-drains.

9. What is the depth of the trickling filter?
a) 0.5-1 m
b) 1-1.5 m
c) 1.5-2 m
d) 2-3 m
Answer: d
Clarification: A typical trickling filter is circular and between 10 meters and 20 meters across and between 2 meters to 3 meters deep. A circular wall, often of brick, contains a bed of filter media which in turn rests on a base of under-drains.

10. The spindle is provided at the ______ to support perforated plates.
a) Edge
b) Bottom
c) Top
d) Centre
Answer: d
Clarification: On the top of the filter media, in the centre is a spindle supporting two or more horizontal perforated pipes which extend to the edge of the media.

11. While designing a trickling filter what would be the depth assumed?
a) 12-15m
b) 4-12 m
c) 16-20 m
d) 20-25 m
Answer: b
Clarification: The depth for trickling filters would be mostly assumed as 4-12 m. Other than this, a trickling filter constitutes a waste water dosing system. Also it constitutes a drain.

12. What is necessary prior to trickling filters?
a) Secondary clarification
b) MBBR
c) Grit chamber
d) Primary clarification
Answer: d
Clarification: Primary clarification is necessary prior to trickling filters. Screening of the materials prior to letting it into the trickling filter is necessary. This is done to prevent clogging.

13. Which type of bacteria are used in trickling filters?
a) Facultative
b) Nitrifying
c) Anaerobic
d) Blue-green bacteria
Answer: a
Clarification: Facultative bacteria are used in trickling filters. Pseudomonas and Alcaligenes are some of the strains used in these filters. Also, Flavobacterium and Achromobacter are also used in this type of treatment.

14. For rock packing low- rate trickling filters what is the hydraulic loading assumed?
a) 1-4 m3/m2.d
b) 4-8 m3/m2.d
c) 8- 12 m3/m2.d
d) 12-15 m3/m2.d
Answer: a
Clarification: 1-4 m3/m2.d is the hydraulic rate considered for rock type of packing in trickling filters. The other type of packing is plastic. While designing this type of packing the hydraulic rate of this would be different.

15. For rock type of packing in intermediate filtration trickling filters what is the hydraulic rate considered?
a) 4-10 m3/m2.d
b) 10-15 m3/m2.d
c) 20-25 m3/m2.d
d) 25-30 m3/m2.d
Answer: a
Clarification: For rock type packing in intermediate filtration trickling type filters, the hydraulic rate considered is 4-10 m3/m2.d. In case of high filtration rock type trickling filters packing it is considered as 10-75 m3/m2.d. For plastic packing type in trickling filters, the hydraulic rate is different.

16. For rock type of roughing packing trickling filter what will be the hydraulic loading rate?
a) 40-200 m3/m2.d
b) 300 m3/m2.d
c) 500 m3/m2.d
d) 600 m3/m2.d
Answer: a
Clarification: For rock type of rough packing trickling filter, the hydraulic loading rate is 40-200 m3/m2.d.High organic loaded waste water have been treated by rough packing filters. However this only partially removes the BOD.

17. For rock type low filtration rate trickling filters what would be the organic loading rate assumed?
a) 0.07-0.22 kg BOD/m3d
b) 0.24-0.48 kg BOD/m3d
c) 0.4-2.4 kg BOD/m3d
d) >2.4 kg BOD/m3d
Answer: a
Clarification: For rock type of low filtration rate trickling filters the organic load assumed is 0.07-0.22 kg BOD/m3d. Intermediate rate filtration filters would have different organic load. It is around 0.24-0.48 kg BOD/m3d.

18. For rock type high filtration rate trickling filters what would be the organic loading rate assumed?
a) 0.07-0.22 kg BOD/m3d
b) 0.24-0.48 kg BOD/m3d
c) 0.4-2.4 kg BOD/m3d
d) >2.4 kg BOD/m3d
Answer: c
Clarification: For rock type of high filtration rate tricking filters, the organic load assumed is 0.4-2.4 kg BOD/m3d. Intermediate rate filtration trickling filters would have different organic load. It is around 0.24-0.48 kg BOD/m3d.

19. For plastic type high filtration rate trickling filters what would be the organic loading rate assumed?
a) 0.07-0.22 kg BOD/m3d
b) 0.24-0.48 kg BOD/m3d
c) 0.5 kg BOD/m3d
d) 0.6-3.2 kg BOD/m3d
Answer: d
Clarification: For plastic type of high filtration rate trickling filters, the organic load assumed is 0.6-3.2 kg BOD/m3d. Roughing rock type of trickling filter has a different organic loading rate. It is > 1.5 kg BOD/m3d.

20. For rock type low filtration rate trickling filters what would be the recycling ratio assumed?
a) 0
b) 1-2
c) >2
d) >3
Answer: a
Clarification: For rock type low filtration, the recycling ratio would be 0. In case of intermediate filtration, this ratio is a little higher. It is around 0-1.