This set of Waste Water Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Reverse Osmosis”.
1. Reverse osmosis helps in mineralizing water.
a) True
b) False
View Answer
Explanation: Reverse Osmosis is commonly called RO and it is a process used to remove minerals and ions from water by pushing it under pressure through a semi-permeable RO membrane.
2. Osmosis is a process where a stronger saline solution will tend to migrate to a weaker saline solution.
a) True
b) False
View Answer
Explanation: Osmosis is a naturally occurring phenomenon and one of the most important processes in nature. It is a process where a weaker saline solution will tend to migrate to a strong saline solution.
3. ______ is used for the RO process.
a) Highly permeable membrane
b) Permeable membrane
c) Semi-permeable membrane
d) Non-permeable membrane
View Answer
Explanation: Reverse Osmosis is commonly called RO and it is a process used to remove minerals and ions from water by pushing it under pressure through a semi-permeable RO membrane.
4. A reverse osmosis membrane is a semi-permeable membrane that allows the passage of _________
a) Water
b) Dissolved salts
c) Organics
d) Bacteria
View Answer
Explanation: Reverse Osmosis is commonly called RO and the process uses a semi-permeable membrane that allows the passage of water alone and holds back the contaminants.
5. In RO, pressure that is greater than the naturally occurring osmotic pressure is applied in order to ______
a) Mineralize water
b) Desalinate water
c) Decompose organics
d) Push bacteria across membrane
View Answer
Explanation: In RO, the pressure that is greater than the naturally occurring osmotic pressure is applied in order to remove salts and ions from the water, allowing pure water through while holding back a majority of contaminants.
6. The amount of pressure to be applied depends on ______
a) Organic content
b) Salt concentration
c) Bacteria
d) Membrane strength
View Answer
Explanation: The amount of pressure required depends on the salt concentration of the feed water. The pressure required to overcome the osmotic pressure is more as the feed concentration increases.
7. The desalinated water is called ________
a) Clean water
b) Clear water
c) Pure water
d) Permeate
View Answer
Explanation: The desalinated water that is demineralized or deionized, is called permeate (or product) water and the water stream with contaminants is called reject stream.
8. What is the other name for reject stream?
a) Permeate
b) Non-concentrated stream
c) Brine stream
d) Polluted water stream
View Answer
Explanation: The other name for the reject stream is the brine stream where the concentration of the pollutants is more.
9. What is the percentage of dissolved salts achieved from the RO unit?
a) 30-40%
b) 50-65%
c) 75-85%
d) 95-999%
View Answer
Explanation: The water that passes through the RO membrane is called permeate or product water and the percentage of dissolved solids is usually 95-99%.
10. The molecular weight greater than _____ is likely rejected by an RO system.
a) 50
b) 100
c) 150
d) 200
View Answer
Explanation: An RO membrane rejects contaminants based on their size and charge. Contaminants having a molecular weight greater than 200 are likely to be rejected by an RO membrane.
11. What is a recovery?
a) Permeate flow/ Feed flow
b) Reject flow/ Feed flow
c) Permeate flow/ Reject flow
d) Feed flow/ Permeate flow
View Answer
Explanation: Recovery is Permeate flow/ Feed flow. Recovery can range from 75% to 85 %. Based on the recovery, the number of membranes is designed.
12. What is salt rejection?
a) 1- salt passage
b) Reject flow X ( 1- salt passage)
c) (1-salt passage)/ reject flow
d) Reject flow/ salt passage
View Answer
Explanation: Salt rejection is defined as 1- salt passage. Salt passage is defined as the ratio of salt in the permeate to that of salt in the feed flow. Salt rejection will differ from one type of membrane to the other.
13. What is the concentration factor?
a) 1/ recovery
b) 1/(1-recovery)
c) 1- recovery
d) Recovery X permeate flow
View Answer
Explanation: Concentration factor is 1/ (1 – recovery). It is the concentration factor of the brine stream. It is calculated by assuming salt passage as zero.
14. How is the permeate flux expressed mathematically?
a) Fw= Kw(∆ p- ∆∏)
b) Fw= ∆ p- ∆∏
c) Fw= Kw∆∏
d) Fw= Kw(∆ p- ∆∏)
View Answer
Explanation: The permeate flux expressed mathematically as Fw= Kw(∆ p- ∆∏). Fw is the water flux. Kw water permeability constant. P is the pressure and ∏ is the osmotic pressure.
15. How is the salt flux expressed mathematically?
a) Fs= Ks ∆ Cs
b) Fs= Ks /∆ Cs
c) Fs= Ks 2∆ Cs
d) Fs= Ks
View Answer
Explanation: The salt flux expressed mathematically as Fs= Ks ∆ Cs. Fs is the solute flux. Cs is the concentration gradient across the membrane. Ks is the permeability constant.
16. What is the average pressure at which the reverse osmosis operates for sea water desalination?
a) 800-1000 psi
b) 1000-2000 psi
c) 2000-3000 psi
d) 5000-8000 psi
View Answer
Explanation: The reverse osmosis is operated usually in the range 800-1000 psi. This however depends on the TDS present in the raw water. This also depends on the surface area of the membrane used.
17. What is the average pressure at which the reverse osmosis operates for treating brackish water?
a) 100-200 psi
b) 250-600 psi
c) 600-800 psi
d) 800-1200 psi
View Answer
Explanation: The reverse osmosis is operated usually in the range 250-600 psi for treating brackish water. This however depends on the TDS present in the raw water. This also depends on the surface area of the membrane used.
18. Calculate the feed flow for a two stage pass for the following data.
Recovery: 85℅
Permeate flow: 100 m3/hr
a) 310 m3/hr
b) 320 m3/hr
c) 325 m3/hr
d) 305 m3/hr
View Answer
Explanation: 2nd stage feed flow: 100/0.65=154m3/hr. 1st stage feed flow= 154/0.5= 308 m3/hr. Total recovery = (0.5 + (1-0.65))= 0.85 which is 85 % recovery.
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