This set of Dairy Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Membrane Filter – 1”.
1. What is the flux of a membrane filter if it contains 75 sq. ft. of filter area and operates for 24 hours at a flow rate of 5 gpm? Assume that the water temperature is 20℃.
a) 100 gallons per square foot per day
b) 98 gallons per square foot per day
c) 76 gallons per square foot per day
d) 59 gallons per square foot per day
View Answer
Explanation: 5 gallons per minute multiplied by 60 minutes per hour multiplied by24 hours per day equals 7200 gallons per day. 7200 gallons per day divided by75 sq. ft. = 96 gallons per square foot per day.
2. What is the specific flux of the system if it contains 75 sq. ft. of filter area and operates for 24 hours at a flow rate of 5 gpm? Assume that the water temperature is 20℃ and the TMP of the system is 20 psi.
a) 5.6 gfd/psi
b) 4.8 gfd/psi
c) 9.4 gfd/psi
d) 5.5 gfd/psi
View Answer
Explanation: We calculated the flux to be 96 gfd. In order to calculate specific flux, divide the flux by the TMP 96 gfd / 20 psi. = 4.8 gfd/psi.
3. Which of the following qualities do not determine the percent recovery in membrane treatment?
a) Membrane filtration level selected
b) Characteristic of membrane itself
c) Quality of feed water
d) Nutritional content of feed
View Answer
Explanation: The three qualities are: membrane filtration level selected; the characteristics of the membrane itself; and the quality of the feed water. These qualities help in determining percentage recovery.
4. Which of the following mechanisms is used by a membrane filter to remove particulate material from the water?
a) Adsorption
b) Settling
c) Straining
d) Crystallization
View Answer
Explanation: Straining has been identified as the principal mechanism that is operative in the removal of suspended solids during the filtration of settled secondary effluent from biological treatment processes. Other mechanisms like interception and adhesion are also operative even though their effects are small and, for the most part, masked by the straining action.
5. The membrane filtration level with the smallest pore size (0.0001 – 0.001 µm) is called_____________
a) Micro filtration
b) Reverse osmosis
c) Nano filtration
d) Ultra filtration
View Answer
Explanation: Reverse Osmosis has a pore size range of 0.0001 – 0.001. It is by far the finest separation material available to industry.
6. The flow rate through the membrane filter itself expressed as a gallon per square foot per day is called?
a) Permeate
b) Head loss
c) Flux
d) Overhead
View Answer
Explanation: Flux is the rate of extraction of permeates measured as a gallon per square foot per day. Permeate is the filtrate, the liquid passing through the membrane.
7. Which one of the following is the name of the process of reversing the direction of water flow through the filter using filtered water?
a) back pulse
b) reverse flow
c) air pressure
d) front pressure
View Answer
Explanation: Applying an external pressure to reverse the natural flow of pure solvent, thus, is reverse osmosis. The process is similar to other membrane technology applications. However, key differences are found between reverse osmosis and filtration. The predominant removal mechanism in membrane filtration is straining, or size exclusion, so the process can theoretically achieve perfect efficiency regardless of parameters such as the solution’s pressure and concentration.
8. The filtered water that has been treated by a membrane filter is called _____________
a) Permeate
b) Concentrate
c) Reject
d) Pulp
View Answer
Explanation: The desalinated water that is de-mineralized or de-ionized, is called permeate (or product) water. The water stream carrying the concentrated contaminants that did not pass through the RO membrane is called the reject (or concentrate) stream.
9. Which of the following remains the primary use of membrane filtration in water treatment?
a) Desalination of salt water to produce potable water
b) A pretreatment step in water treatment
c) Filtration of surface or ground water under the direct influence of surface water
d) Pre heating
View Answer
Explanation: Primary use of Membrane filtration is desalination of salt water to produce portable water in water treatment. All other options are secondary uses.
10. Which of the following are different forms of membrane filter construction?
I) Hollow filter
II) TMP
III) Spiral wound
IV) Ceramic
V) Cross flow
VI) Electro dialysis
a) I), III) IV) and VI)
b) I),II),III) and IV)
c) I) and II)
d) III) and IV)
View Answer
Explanation: Hollow filters, TMP, Ceramic and Electro dialysis are different forms which constitute material of membrane filter. Cross flow is the type of flow and TMP is Trans-membrane pressure.
11. A raw water reservoir would be an example of which membrane pretreatment method (where the goal is to reduce the loading and fouling potential of the water fed to the membrane)?
a) Filtration
b) Clarification
c) Chemical treatment
d) Pasteurization
View Answer
Explanation: The raw water reservoir would act as clarifier. It helps in clarification and reduction of fouling potential of water fed to a membrane.
12. Which of the following is a valid name for a test for testing membrane integrity?
a) Flux membrane test
b) Reversal of flow test
c) Air pressure hold test
d) Sediment test
View Answer
Explanation: There are 3 major tests used to determine the integrity of a membrane filter: the Bubble Point Test, the Forward Flow Test, and the Pressure Hold Test. All three tests are based on the same physics mechanism that the flow of a gas through a liquid-wetted membrane under applied gas pressures.
13. Chlorines, acids, and bases are three types of chemicals used to do which of the following?
a) prescreen the water in the membrane filtration system
b) chemically clean a membrane filtration system
c) monitor a membrane filtration system for fiber failure
d) filter
View Answer
Explanation: Chlorines, acids and bases are used to chemically clean a membrane filtration system. They ensure maximum efficiency of the system.
14. Which of the following mechanisms is not used by a membrane filter to remove particulate material from the water?
a) flux
b) reverse flow
c) particle counts
d) chlorine
View Answer
Explanation: Reverse flow is basically a flow method. Flux, particle count and chlorine are mechanisms used to remove particulate material from water.
15. For surface water system, the required residual disinfectant concentration may not be less than _______ mg/L for more than ___________ hours before the first customer.
a) 0.2, 6
b) 2.0, 6
c) 0.2, 4
d) 2.0, 4
View Answer
Explanation: The residual disinfectant concentration required is equal to or more than 0.2mg/L. This should be applied 6 hrs before the 1st usage.
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