Category: WASTE WATER Engineering Objective Questions

250+ TOP MCQs on Autoclaves and Answers

Waste Water Engineering Multiple Choice Questions on “Autoclaves”.

1. ________ is a pressure chamber used to carry out processes at high temperature and pressure.
a) Oven
b) Micro clave
c) Autoclave
d) Hot air oven
Answer: c
Clarification: An autoclave is a pressure chamber used to carry out industrial processes requiring elevated temperature and pressure different from ambient air pressure. Autoclaves are used in medical applications.

2. Autoclaves are used in the medical applications to perform ______
a) Vulcanization
b) Sterilization
c) Heating
d) Cleaning
Answer: b
Clarification: Autoclaves are used in medical applications to perform sterilization and in the chemical industry to cure coatings and vulcanize rubber for hydrothermal synthesis. There are other industrial applications also.

3. What is the common temperature used in autoclaves?
a) 121˚C
b) 109˚C
c) 135˚C
d) 142˚C
Answer: a
Clarification: Many autoclaves are used to sterilize the equipment and supplies by subjecting them to high-pressure saturated steam at 121 °C (249 °F) for around 15–20 minutes depending on the size of the load and the contents.

4. Who invented the autoclave?
a) Pasteur
b) Charles Chamberland
c) Arnold O. Beckman
d) Antonie van Leeuwenhoek
Answer: b
Clarification: Pasteur invented hot air oven. Charles Chamberland invented autoclave. Arnold O. Beckman invented pH meter. Antonie van Leeuwenhoek is considered as the father of microbiology.

5. All the trapped air is removed from the autoclave before activation.
a) True
b) False
Answer: a
Clarification: It is very important to ensure that all of the trapped air is removed from the autoclave before activation, as trapped air is a very poor medium for achieving sterility. Sterilization can be achieved in three minutes by steam at 134˚C.

6. A device that uses steam to sterilize equipment and other objects is a medical autoclave.
a) True
b) False
Answer: a
Clarification: Autoclaves are found in many laboratories, medical fields, institutions and other places that need to ensure the sterility of an object. This means that all bacteria, fungi, viruses and spores are inactivated.

7. What is the inner surface of autoclaves made of?
a) Mild steel
b) Stainless steel
c) Copper
d) Aluminum
Answer: b
Clarification: There is a horizontal and vertical type of autoclave. In vertical autoclaves, the whole autoclave is made of stainless steel and the outer surface is made of mild steel. Vertical autoclaves are used mainly for the sterilization process.

8. What is the operating temperature for table top steam sterilizer?
a) 110-115 ˚C
b) 121-130˚C
c) 121-135˚C
d) 121˚C
Answer: c
Clarification: The sterilization temperature for high pressure sterilizer of a rectangular model is 121˚C. The operating temperature for high pressure sterilizer of rectangular model is 121˚C to 135˚C.

9. The sterilizer of pressure cooker type is made of ________
a) Aluminium
b) Steel
c) Stainless steel
d) Copper
Answer: a
Clarification: The sterilizer of pressure cooker type is made of aluminium for quick transfer of heat, which generates steam under pressure. The sterilizer is subjected to the saturated steam environment for preset specified time as soon as it reaches the right temperature.

10. Which type of autoclaves is mainly used for bulk research work?
a) Vertical autoclave
b) Horizontal autoclave
c) Sterilization pressure cooker
d) Table top steam sterilizer
Answer: b
Clarification: Horizontal autoclaves are mainly used for institutions or laboratory for doing bulk sterilizing research work. These autoclaves have double walled inside and outside made of stainless steel of 304 quality.

11. Which type of control valve can be used for 90-degree change in direction of flow?
a) Butterfly valve
b) Diaphragm valve
c) Globe valve
d) Gate valve
Answer: c
Clarification: Globe valves are the only ones which can be used for 90 degree change in direction of flow. Specifically angle- globe valves are used for that purpose. Globe valves are not used for controlling pressure.

12. Which of these is a linear motion control valve?
a) Ball valve
b) Butterfly valve
c) Plug valve
d) Diaphragm valve
Answer: d
Clarification: Control valves are classified as linear and rotary motion valves. Diaphragm and Globe valves are classified as linear motion control valve. Whereas Ball, Butterfly and plug valves are classified as rotary motion control valves.

13. Which of the following is not a type of control butterfly valve?
a) Single off-set
b) Concentric
c) Triple off-set
d) Concentric centreline
Answer: b
Clarification: Control butterfly valves are of 4 types. Single offset, double offset, triple offset and concentric centreline. There is no type of control butterfly such as concentric.

14. What is inherent flow characteristics?
a) The curve obtained between control valve capacity and valve stem travel
b) The curve obtained between control valve capacity and Cv
c) The curve obtained between Cv and valve stem travel
d) The curve obtained between control valve capacity and pressure drop
Answer: a
Clarification: The curve between control valve capacity and valve stem travel is known as inherent flow characteristics. This curve is obtained at a constant pressure drop. The relationship between control valve capacity and valve stem travel is known as flow characteristic of the control valve.

15. Which type of valve is preferred for sequential operations?
a) Electric actuated control valve
b) Single acting control valve
c) Quick opening valve
d) Double acting control valve
Answer: c
Clarification: Quick opening valves are used for sequential processes. These are used in batch and semi-continuous process. These are self- actuated valves.

16. Which of these control valves has the lowest pressure recovery?
a) Globe valve
b) Ball valve
c) Butterfly valve
d) Plug valve
Answer: a
Clarification: Globe valves have lower pressure recovery than the ball, plug and butterfly valves. The velocity is very high at the vena contracta. As the liquid flows further down due to the increase in an area the velocity decreases and there is an increase in pressure. This phenomenon is known as pressure recovery.

17. Which type of actuator is preferred when high and fast stroking speed is required?
a) Direct acting actuator
b) Reverse acting actuator
c) Electro hydraulic actuator
d) Piston actuator
Answer: d
Clarification: Piston actuators are preferred when high and fast stroking speed is required. This type of actuator utilises air pressure upto 150psig. This eliminates the need for a pressure regulator.

18. Direct acting actuators fall under which category of actuator?
a) Diaphragm actuator
b) Piston actuator
c) Electro hydraulic actuator
d) Manual actuators
Answer: a
Clarification: Direct actuator is a type of Diaphragm actuator. Another type of diaphragm actuator is reverse acting actuator. The size of these actuators depends on the air supply required.

19. The gain of a control valve should never be less than _______
a) 1
b) 5
c) 0.5
d) 0.75
Answer: c
Clarification: The gain of a control valve should never be lesser than 0.5. Gain is defined as the ratio between the differences in flow to the differences in stoke or travel. In case the value is lesser than 0.5 then there would be a problem in controlling the valve.

20. What should be the rangeability of the control valve?
a) Gain
b) Cv
c) Turndown
d) Stoke%
Answer: c
Clarification: Rangeability should be greater than the turndown of a control valve. The ratio of the Cv at which the valve is fully open to the minimum Cv at which it can control is known as rangeability. Turndown is the ratio of the calculated Cv at the maximum condition to that of the Cv calculated at the minimum condition.

250+ TOP MCQs on Methods of Sludge Processing and Disposal – 2 and Answers

Waste Water Engineering Interview Questions and Answers for freshers on “Methods of Sludge Processing and Disposal – 2”.

1. What is the percentage of dry solids for the primary sludge assumed at the outlet of aerobic digester?
a) 1-2.5%
b) 7-10.5%
c) 2.5-7%
d) 10.5-12.5%
Answer: c
Clarification: The percentage of dry solid assumed at the outlet of an aerobic digester for the primary sludge is 2.5-7%. In most cases, it is considered as 3.5%. This however depends on the water constituents.

2. In the case of anaerobic digestion, what is the percentage of dry solids for the primary sludge considered at the outlet?
a) 2-5%
b) 1-2%
c) 10-12%
d) 7-9%
Answer: a
Clarification: The percentage of dry solids for the primary sludge at the outlet of the anaerobic digester is considered as 2-5%. Generally, it is considered 4%. This however depends on the water constituents.

3. What is the concentration of polymer added to a belt filter press handling the primary sludge?
a) 2-5 kg/Mg dry solids
b) 1-4 kg/Mg dry solids
c) 5-10 kg/Mg dry solids
d) 10-12 kg/Mg dry solids
Answer: b
Clarification: 1-4 kg/Mg dry solids is the concentration of the polymer that is added to the belt filter press handling primary sludge. In case of centrifuge the concentration would be 1-2.5 kg/Mg dry solids. Polymer doses will vary according to molecular weight and ionic strength.

4. Heat treatment involves heating of the sludge. The supernatant from the heat treatment system is rich in ___________
a) TDS
b) TSS
c) BOD
d) Heavy metals
Answer: c
Clarification: The supernatant is rich in BOD. Thus this requires to be recycled to the treatment plant in order to be treated again. Heat treatment of the sludge is done in order to condition the sludge.

5. What is the maximum temperature up to which conditioning can be conducted?
a) 50 degree
b) 70 degree
c) 60 degree
d) 40 degree
Answer: c
Clarification: The maximum temperature up to which the sludge can be heated in order to carry out conditioning is 60 degree. By heating the sludge the soluble BOD increases which are contained in the supernatant. This sludge preheating method enhances the dewatering performance.

6. What is the temperature at which sludge has to be frozen in order to carry out conditioning?
a) -2 to -5 degree
b) -20 to -25 degree
c) -5 to -8 degree
d) -10 to -20 degree
Answer: d
Clarification: The temperature at which the sludge has to be frozen in order to carry out conditioning is -10 to -20 degree. This should be frozen for at least 30 mins. This technology works on even difficult-to-dewater sludge.

7. What is the concentration of solids in the filtrate after thawing and freezing?
a) 45-50%
b) 50-60%
c) 25-40%
d) 60-65%
Answer: c
Clarification: The concentration of solids in the filtrate would be 25-40% after the sludge is thawed. This would contain the very low concentration of TSS. The time required to freeze/thaw the sludge depends on the concentration of solids present in the sludge.

8. Out of the below given methods which of these have the lowest capital cost?
a) Sludge drying bed
b) Filter press
c) Centrifuge
d) Sludge lagoons
Answer: a
Clarification: Sludge drying bed has the lowest capital cost. It has low consumption of chemicals too. However, sludge removal is labour intensive.

9. Out of the below given methods which of these have the highest cake solids concentration?
a) Sludge drying bed
b) Recessed plate Filter press
c) Centrifuge
d) Sludge lagoons
Answer: b
Clarification: A recessed plate filter press yields the highest cake solid formation while handling sludge disposal. However, it has low suspended solids in filtrate. The capital cost in this treatment method is high.

10. Out of the below given methods which of these is operated in batch process?
a) Sludge drying bed
b) Belt Filter press
c) Centrifuge
d) Sludge lagoons
Answer: b
Clarification: The belt filter press is operated in batch process. The operation and maintenance cost for these equipments is very high. It also requires high labour cost.

11. Out of the below given methods which of these requires a grit removal prior to it?
a) Sludge drying bed
b) Filter press
c) Centrifuge
d) Sludge lagoons
Answer: c
Clarification: A centrifuge requires a grit removal prior to it, in order to remove the grit particles. This has a low capital cost. It has moderately suspended solids in the centrate.

12. Out of the below given methods which of these produce an odour?
a) Sludge drying bed
b) Belt Filter press
c) Centrifuge
d) Recess plate filter press
Answer: b
Clarification: A belt filter press produces an odour. The high pressure machines produce very dry cakes. Generally, automatic operation is not advised for these equipment.

13. Out of the below given methods in which of these organic matters is stabilized?
a) Sludge drying bed
b) Filter press
c) Centrifuge
d) Sludge lagoons
Answer: d
Clarification: In sludge lagoons, the organic matter is stabilised. Low capital cost is involved in this method. However large space is required to carry out this process.

14. Out of the below given methods in which of these does the sludge contain 70-80% moisture?
a) Sludge drying bed
b) Filter press
c) Centrifuge
d) Sludge lagoons
Answer: c
Clarification: In a centrifuge the sludge cake produced contains approximately 70-80 % water. The solid concentration varies from 10-30 %. The centrate contains very low TSS.

15. What is the general size of belt available in the markets for a belt filter press?
a) 0.5 -3.5 m
b) 4-6 m
c) 7-9m
d) <0.5m
Answer: a
Clarification: Generally the size of the belt in the belt filter press is 0.5-3.5 m. In most cases, a belt of width 2m is used. Sludge loading rate varies from 90-680 kg/mh depending on the sludge type.

Waste Water Engineering for Interviews,

250+ TOP MCQs on High Rate Filtration and Answers

Waste Water Engineering Multiple Choice Questions on “High Rate Filtration”.

1. High rate filtrations cannot be used for wet weather conditions.
a) True
b) False
Answer: a
Clarification: The purpose of this technique is to reduce contaminant load due to the discharge under wet weather conditions. In addition, by reducing the filtration rate under dry weather conditions, the process can be operated as a substitute for the primary settling tank without chemicals addition.

2. What is the filter media made of?
a) Cotton
b) Synthetic fibre
c) Geotextiles
d) Plastic
Answer: b
Clarification: The filtering media is made by synthetic fibre specially processed and has a high void ratio(95% and above), which enables the trapping of debris and suspended solids in and out of the media simultaneously.

3. Filter cycle is interrupted for ______
a) Air washing
b) Back washing
c) Adding influent
d) Removing effluent
Answer: a
Clarification: Filtration cycle is interrupted for air washing when filter resistance through the filter media reaches the terminal filtration.

4. ________ is shifted to keep an ample space for filtering media to rotate.
a) Drain
b) Movable plate
c) Perforated plate
d) Cylinder
Answer: b
Clarification: Washing of the filtering media is made when the movable plate, which retains filter bed, is shifted to keep an ample space for filtering media to rotate. The suspended solids captured by the filtering media are removed by the air washing.

5. What is the void ratio of filter media?
a) 60-65 %
b) 65-70 %
c) 75-80 %
d) 80-85 %
Answer: d
Clarification: The diameter of synthetic fiber balls used in the filter media is 1.5 cm. The void ratio of the filter media usually lies in the range of 80-85 %. The filter media is usually chemical and temperature resistant.

6. The synthetic fibres used are temperature resistant.
a) True
b) False
Answer: a
Clarification: Synthetic fibre is used as the filter media. The filter media is usually chemical and temperature resistant. The filter media is usually chemical and temperature resistant.

7. Which of the following is not true in case of closing the top of the vessel?
a) Keeps out sunlight
b) Limits algal growth
c) Restricts bug access
d) Eliminates odour
Answer: d
Clarification: The top of the vessel is closed to keep out the sunlight which limits algae growth and to restrict bug access to the water level. The closing of the vessel might in fact build up an odour of its own.

8. As the compression increases, the porosity in filter bed _____
a) Increases
b) Decreases
c) Remains constant
d) Alters
Answer: b
Clarification: As the compression changes, the porosity in the filter bed also changes. The increase in compression results in smaller voids to capture smaller particles. Less compression leads to larger voids to capture larger particles.

9. What is the life of the media used?
a) 2 years
b) 5 years
c) 8 years
d) 10 years
Answer: d
Clarification: The media used is synthetic fibre. It removes particles of size equal to 4 microns. 0% to 40% of compression can be done in the bed. The life of the media is approximately equal to 10 years.

10. What is the percentage of wash water?
a) >5%
b) >3%
c) >2%
d) <2%
Answer: d
Clarification: The wash time is 30 minutes. The filter must be cleaned for every 8-24 hours. The wash water volume is less than 2% of the total volume of water used for the purpose.

11. Which of these does high rate filters not remove?
a) Phosphorous
b) Suspended Solids
c) Colloidal Solids
d) Organic matter(particulate)
Answer: d
Clarification: High rate filters remove suspended solids and colloidal solids. They also remove phosphorous compounds. They don’t remove organic matter (particulate).

12. Which of these has been used as a medium for high rate filtration?
a) Polyvaniladene
b) Polypropylene
c) Polyacetylene
d) Polyvinyl
Answer: a
Clarification: Polyvaniladene has been used as a medium in case of high rate filtration. This is a synthetic medium. This is highly porous.

13. What is the porosity of these synthetic media?
a) 90-92%
b) 92-94%
c) 88-90%
d) 94-96%
Answer: c
Clarification: The porosity of such synthetic media is around 88-90%. These media are highly porous. Hence this is highly efficient in the removal of colloidal and suspended solids.

14. While designing a high rate filter what would be the velocity assumed?
a) 12m/h
b) 18 m/h
c) 7 m/h
d) 5 m/h
Answer: d
Clarification: The velocity of the high rate filters are assumed as 5 m/h. Based on this, the diameter of the filter is fixed. Also the amount of media calculated is also based on this.

15. For a high rate filter calculate the diameter of the filter required for a flow of water of 200 m3/h.
a) 7.2m
b) 8.4 m
c) 14 m
d) 13 m
Answer: a
Clarification: The calculated diameter is 7.2. Area = 200/5. Diameter =square root (area x 1.27) = 7.2 m.

16. What is the bed depth of the sand considered in such rapid filters?
a) 500 mm
b) 200- 400 mm
c) 600-760 mm
d) 900- 1000 mm
Answer: c
Clarification: The bed depth is considered as 600-760 mm. The depth for the gravels is considered as 400-600 mm. These are the assumptions made while designing a rapid sand filtration.

250+ TOP MCQs on Moving Bed Reactor and Answers

Waste Water Engineering Multiple Choice Questions on “Moving Bed Reactor”.

1. _______ flows along with the reactants in MBR.
a) Pollutants
b) Microbes
c) Disinfectants
d) Catalytic materials
Answer: d
Clarification: The catalytic material flows along with the reactants and is then separated from the exit stream and recycled in moving bed bioreactors.

2. Moving bed reactors are closed systems.
a) True
b) False
Answer: b
Clarification: Moving bed reactors are catalytic reactors in which the catalyst moves through the reactor along with the reactants. They are open systems and operate at steady state.

3. Reactants enter from the bottom in MBR.
a) True
b) False
Answer: b
Clarification: Reactants and catalyst enter the top of the reactor and move through the vessel. Once at the bottom the catalyst is removed and regenerated, products are removed from the reaction system and the catalyst is regenerated and brought to the top of the reactor.

4. Which of the following is an advantage of MBR?
a) Heat transfer
b) Fluid reactant
c) Solid distribution
d) Selectivity
Answer: d
Clarification: In moving bed bioreactors catalyst is easy to regenerate, the handling cost of a catalyst is low and has plug flow characteristics with good selectivity.

5. Which of the following is a disadvantage of MBR?
a) Catalyst regeneration
b) Flow characteristics
c) Catalyst cost
d) Heat transfer
Answer: d
Clarification: In moving bed reactor, the flow of solids is not easy to maintain and solid distribution is also difficult. It consists of poor heat transfer characteristics. The fluid reactant may bypass catalyst bed.

6. What is the load considered for biox media?
a) 1.8 kg/ m3
b) 2.6 kg/ m3
c) 6 kg/m3
d) 3.6 kg/m3
Answer: a
Clarification: The load considered for biox media is 1.8 kg/ m3. These media are immersed in aeration tank. This increases the degradation of BOD.

7. Calculate the volume of the tank for the following information.
BOD: 400 mg/L
Flow: 3500 m3/h
Loading rate of media: 3.5 Kg/ m3/day
a) 9600 m3
b) 9000 m3
c) 2000 m3
d) 4000 m3
Answer: d
Clarification: BOD load= BOD X flow rate. Volume of tank = BOD load/ loading rate of media. Volume of tank= {(400 X 3500 x24)/1000}/3.5=9600 m3.

8. What is the depth of biox media generally considered for an aeration tank?
a) 1.2 m
b) 3 m
c) 5 m
d) 2.5 m
Answer: a
Clarification: The depth for bioxmedia is considered generally as 1.2 m. The total liquid depth for a tank is depth of biox media + liquid depth above biox media + liquid depth below biox media. The bio media increases the efficiency to degrade BOD.

9. What is the efficiency in reducing the BOD of a tank consisting f Biox media
a) 90%
b) 80%
c) 85%
d) 95%
Answer: a
Clarification: The efficiency in reducing the BOD of a tank consisting of Biox media is 90 %. In normal activated sludge process this is around 70%. These media also reduce SRT of the tank when compared to the conventional Activated sludge process.

10. Calculate the area required for the system consisting of biox media for the following data.
Flow: 500 m3/h.
BOD: 500 mg/L
a) 8 m3
b) 3.4 m3
c) 3 m3
d) 4.4 m3
Answer: b
Clarification: BOD load= BOD X flow rate. Volume of tank = BOD load/ loading rate of media. Volume of tank= {(500 X 500 x24)/1000000}/1.8=3.4 m3.

250+ TOP MCQs on Adsorption and Water Treatment and Answers

Waste Water Engineering Multiple Choice Questions on “Adsorption and Water Treatment”.

1. Adsorption is an endothermic process.
a) True
b) False
Answer: b
Clarification: The phenomenon of adsorption is essentially an attraction of absorbable molecules to an adsorbent surface. Adsorption is nearly always an exothermic process.

2. Chemical adsorption takes place at high temperature.
a) True
b) False
Answer: a
Clarification: Chemical adsorption takes place at high temperature whereas physical adsorption takes place at low temperature and is reversible.

3. Which force holds the molecules in physical adsorption?
a) Friction force
b) Van der waals force
c) Tension force
d) Nuclear force
Answer: b
Clarification: It is the common type of adsorption. The basic feature of physical adsorption is that the adsorbate molecules are held at the surface of the adsorbent by weak van der Waals forces. These are the forces that exist between particles of all matter.

4. What is the lowest enthalpy of adsorption for physical adsorption?
a) 5 KJ mol-1
b) 10 KJ mol-1
c) 15 KJ mol-1
d) 25 KJ mol-1
Answer: b
Clarification: The physical adsorption is observed on the surface of any solid only. The extent of adsorption varies according to the nature of the adsorbent and adsorbate. Physical adsorption is characterized by low enthalpy of adsorption that is about 10-40 KJ/ mol.

5. What is the highest enthalpy of adsorption for chemical adsorption?
a) 100 KJ mol-1
b) 200 KJ mol-1
c) 300 KJ mol-1
d) 400 KJ mol-1
Answer: d
Clarification: The enthalpy of chemisorption is as high as that of chemical bonds (bond enthalpies) and is in the range of 40 – 400 kJ mol-1. Like most of the chemical changes, it is irreversible.

6. Physical adsorption is also called as _________
a) Adsorption
b) Absorption
c) Physisorption
d) Sorption
Answer: c
Clarification: Physical adsorption is also called as Physisorption. Since physical adsorption is an exothermic process, it occurs more readily at lower temperatures and decreases with increase in temperature.

7. Chemical adsorption is also called as _____
a) Sorption
b) Chemisorption
c) Chemiption
d) Chemical sorption
Answer: b
Clarification: Chemical adsorption is also called as chemisorption. The range of enthalpy for chemisorption is as high as that of chemical bonds and is of 40 – 400 kJ mol-1.

8. Physical adsorption ________ with increase in temperature.
a) Decreases
b) Increases
c) Remains same
d) Fluctuates
Answer: a
Clarification: Since physical adsorption is an exothermic process, it occurs more readily at lower temperatures and decreases with increase in temperature.

250+ TOP MCQs on Fouling and Scaling of Membranes and Answers

Waste Water Engineering Multiple Choice Questions on “Fouling and Scaling of Membranes”.

1. What is the percentage of earth’s salt water?
a) 97%
b) 97.1%
c) 97.2%
d) 97.3%
Answer: c
Clarification: 97.2% of earth’s water is salt water which cannot be used for drinking, agricultural and many industrial purposes. Only 0.6% of earth’s water resources are fresh water and due to the unequal spatial distribution of water reserves and increasing populations, the per capita availability of fresh water is decreasing.

2. The formation of the alkaline scale is a function of the operational temperature.
a) True
b) False
Answer: a
Clarification: In addition to pH, the formation of alkaline scale is a function of the operational temperature. Calcium carbonate may form up to a temperature of 95 °C while Mg(OH)2 mainly forms above temperatures of 95-100°C due to the increase in hydroxyl formation with increasing temperature.

3. What is the average permeating of SiO2 in reverse osmosis?
a) 0.2-0.3
b) 0.4-0.6
c) 0.6-0.8
d) 0.8-1
Answer: c
Clarification: SiO2 scaling has been observed in reverse osmosis permeators despite a silica scaling index of only 0.6-0.8 i.e. the concentrate is under saturated with Si02.

4. ________ is a process whereby a solution or a particle is deposited on a membrane surface or in membrane pores.
a) Deposition
b) Absorption
c) Membrane fouling
d) Membrane accumulation
Answer: c
Clarification: When a solution or a particle is deposited on a membrane surface or in membrane pores it is called membrane fouling. It usually occurs in processes such as membrane bioreactor, ultrafiltration, microfiltration or nanofiltration.

5. What is the average pore diameter of NF270?
a) 0.52 nm
b) 0.64 nm
c) 0.76 nm
d) 0.84 nm
Answer: d
Clarification: The average pore diameter of NF270 is 0.84 nm, the percentage of sodium ion rejection is 35.8% and that of calcium ion rejection is 57.5%.

6. What is the surface roughness of the BW30 membrane?
a) 60 nm
b) 62.6 nm
c) 64.5 nm
d) 66.2 nm
Answer: b
Clarification: The surface roughness of BW30 is 62.6 nm and that of NF270 is 4.1 nm. The sodium ion rejection is 35.8% and that of calcium ions is 57.5%.

7. What is the surface roughness of NF270 membrane?
a) 3.6 nm
b) 4.1 nm
c) 5.3 nm
d) 6.8 nm
Answer: b
Clarification: The surface roughness of NF270 membrane is 4.1 nm and that of BW30 is 62.6 nm. The percentage of sodium ion rejection is 35.8% and that of calcium ion rejection is 57.5%.

8. Operating conditions also affect fouling of the membrane.
a) True
b) False
Answer: a
Clarification: membrane fouling is influenced by numerous factors such as system hydrodynamics, operating conditions, membrane properties, and material property (solute).

9. Which of the following factors does membrane fouling does not depend on?
a) Solute
b) Operating conditions
c) Climate
d) Hydrodynamics
Answer: c
Clarification: At low pressure, low feed concentration, and high feed velocity, concentration polarisation effects are minimal and flux is almost proportional to trans-membrane pressure difference.

10. Which of these pollutants cause biofilm formation?
a) Calcium sulphate
b) Silica
c) Calcium carbonate
d) Oxides
Answer: d
Clarification: Fouling is caused by choking of the membranes. This reduces the efficiency of the membranes. Oxides forms biofilm which fouls the membranes.

11. Which of these do not cause scaling of the membranes?
a) Organic and inorganic colloids
b) Calcium sulphate
c) Silica
d) Calcium carbonate
Answer: a
Clarification: The organic and inorganic colloids do not cause scaling of the membranes. Scaling is caused by silica and calcium salts. This is also caused by metal oxide formation.

12. How can biofilm formation be prevented?
a) By installing a microfilter prior to Reverse Osmosis
b) By installing a nanofilter prior to Reverse Osmosis
c) By installing a ultrafilter prior to Reverse Osmosis
d) By installing a pressure sand filter prior to Reverse Osmosis
Answer: a
Clarification: Biofilm formation causes fouling in membranes. Fouling reduces the efficiency of membranes. This can be reduced by installing a microfilter prior to Reverse Osmosis.

13. How can scaling be prevented?
a) By adding sodium hydroxide
b) By adding lime
c) By adding HCl
d) By adding alum
Answer: c
Clarification: Scaling is another factor which results in fouling. This can be prevented by adding HCl. Adding acids prevents fouling.

14. What is the SDI assumed for nanofiltration?
a) 4-6
b) 0-2
c) 2-4
d) 6-8
Answer: b
Clarification: The SDI assumed for nanofiltration is 0-2. The SDI is the silt density index. SDI is a measure of the fouling index.

15. What is the SDI assumed for reverse osmosis spiral wound?
a) 0-2
b) 5-9
c) 9-13
d) 13-15
Answer: a
Clarification: The SDI assumed for reverse osmosis is 0-2. The SDI is the silt density index. SDI is a measure of the fouling index.

16. What is the SDI assumed for reverse osmosis hollow fibre?
a) 4-6
b) 0-3
c) 6-8
d) 8-10
Answer: b
Clarification: The SDI assumed for reverse osmosis hollow fibre is 0-2. The SDI is the silt density index. SDI is a measure of the fouling index.

17. What is the MFI in s/L2 assumed for nanofiltration?
a) 0-10
b) 20-25
c) 12-15
d) 15-20
Answer: a
Clarification: MFI is known as the modified fouling index. This is an index to measure membrane fouling. It is measured in s/L2. The MFI in s/L2 assumed for nanofiltration is 0-10.

18. What is the MFI in s/L2 assumed for reverse osmosis hollow fibre?
a) 0-2
b) 6-8
c) 8-12
d) 12-16
Answer: a
Clarification: MFI is known as a modified fouling index. This is an index to measure membrane fouling. It is measured in s/L2. The MFI in s/L2 assumed for reverse osmosis for the spiral wound is 0-2.

19. What is the MFI in s/L2 assumed for reverse osmosis spiral wound?
a) 2-6
b) 6-10
c) 0-2
d) 14-18
Answer: c
Clarification:MFI is known as a modified fouling index. This is an index to measure membrane fouling. It is measured in s/L2. The MFI in s/L2 assumed for reverse osmosis for the spiral wound is 0-2.