Waste Water Engineering Multiple Choice Questions on “Ion Exchange Design”.
1. The breakthrough curves for ion exchange column and adsorption column are dissimilar.
a) True
b) False
Answer: b
Clarification: The breakthrough curves for an ion exchange column and an adsorption column are similar. The contacting techniques are almost identical. The same procedures used for the design of adsorption columns may be used for ion exchange columns.
2. The area ________ the breakthrough curve is equal to the maximum amount of ions removed by the column.
a) Above
b) Below
c) At
d) Above and below
Answer: a
Clarification: At complete exhaustion, C = Co and the area above the breakthrough curve is equal to the maximum amount of ions removed by the column. At complete exhaustion, the entire exchange column is in equilibrium with the influent and effluent flows.
3. Macroporous resins are required for demineralisation.
a) True
b) False
Answer: b
Clarification: Macroporous resins are normally not required for demineralisation or softening. All styrenic WBA resins are Macroporous. Special particle sizes are required depending on the design technology.
4. What is the acceptable pressure drop at maximum flow rate?
a) 0.5 bar
b) 1.5 bar
c) 2 .5 bar
d) 3.5 bar
Answer: b
Clarification: There is no limit in height, except that the pressure drop at the maximum flow rate should not exceed 100 to 150 kPa (1 to 1.5 bars) at maximum flow rate with clean resins.
5. What is the minimum flow rate for SAC resins?
a) 25 m/h
b) 30 m/h
c) 40 m/h
d) 50 m/h
Answer: a
Clarification: For SAC resins, that have the highest specific gravity, the linear flow rate must be comprised between 25 and about 70 m/h (at about 20 °C). Other resins have a lower specific gravity and are compacted at a lower flow rate, the minimum being about 16 m/h.
6. What is the maximum silica content in treated water from a regeneration system?
a) 10 µg/L
b) 15 µg/L
c) 20 µg/L
d) 25 µg/L
Answer: d
Clarification: To a minor extent, temperature may affect the residual silica leakage in the treated water at temperatures higher than about 50 °C; silica is hardly removed by strongly basic anion exchange resins.
7. The production run should be _______ the regeneration process.
a) Shorter than
b) Longer than
c) Equal to
d) Nearer to
Answer: d
Clarification: The practical limit is that the production run should be at least as long as the regeneration process. As most ion exchange systems are regenerated automatically, the duration of the production run does not have to be “at least one day” as was the rule at the time (many decades ago) when the morning shift would regenerate manually every day at 7 o’clock. Efficient systems have been designed with running times as short as 3 hours.
8. What is the minimum flow rate for water treatment?
a) 5 m3/h per m3 of resin
b) 10 m3/h per m3 of resin
c) 15 m3/h per m3 of resin
d) 20 m3/h per m3 of resin
Answer: a
Clarification: The minimum flow rate for water treatment is 5 m3/h/m3 of resin and the maximum flow rate is 50 m3/h/m3 of resin.
9. What is the maximum operating flow for mixed bed units?
a) 12 BV/h
b) 13 BV/h
c) 14 BV/h
d) 15 BV/h
Answer: d
Clarification: Specific flow rate is between 5 and 50 bed volumes per hour (BV/h) and operating flow is a minimum of 12-15 BV/h. The system should be made as small as possible for economical reasons.
10. Which is the year zeolite was used as ion exchange water softeners?
a) 1900
b) 1905
c) 1925
d) 1945
Answer: b
Clarification: In 1905, Gans, a German chemist, used synthetic aluminosilicate materials known as zeolites in the first ion exchange water softeners. Although aluminosilicate materials are rarely used today, the term “zeolite softener” is commonly used to describe any cation exchange process.
11. _________resins can neutralize strong bases.
a) SAC
b) WAC
c) SBA
d) WBA
Answer: a
Clarification: SAC stands for Strong Acid Cation. SAC resins can neutralize strong bases and convert neutral salts into their corresponding acids. SBA resins can neutralize strong acids and convert neutral salts into their corresponding bases. These resins are utilized in most softening and full demineralization applications.
12. Calculate the amount of resin required for the following information.
Cation Load: 10 ppm as CaCO3
Capacity: 47 Kg/m3
Correction factor: 0.9
Flow rate: 135 m3/hr
Operation hours: 20 hrs
a) 0.5 m3
b) 1.5 m3
c) 0.6 m3
d) 2.5 m3
Answer: c
Clarification: Cation load= Cation as CaCO3 x Flow rate x Operating hours/1000. Resin Volume= Cation load/ (Exchange capacity x Correction factor). Resin Volume =[(10 x 135 x 20)/1000]/(47 x 0.9)= 0.6 m3.
13. Calculate the amount of resin required for the following information.
Cation Load: 30 ppm as CaCO3
Capacity: 47 Kg/m3
Correction factor: 0.9
Flow rate: 135 m3/hr
Operation hours: 20 hrs
a) 1.5 m3
b) 1.8 m3
c) 0.6 m3
d) 2.5 m3
Answer: b
Clarification: Cation load= Cation as CaCO3 x Flow rate x Operating hours/1000. Resin Volume= Cation load/ (Exchange capacity x Correction factor). Resin Volume =[(30 x 135 x 20)/1000]/(47 x 0.9)= 1.8 m3.
14. Calculate the amount of resin required for the following information.
Cation Load: 80 ppm as CaCO3
Capacity: 47 Kg/m3
Correction factor: 0.9
Flow rate: 135 m3/hr
Operation hours: 20 hrs
a) 4.5 m3
b) 4.8 m3
c) 0.6 m3
d) 2.5 m3
Answer: b
Clarification: Cation load= Cation as CaCO3 x Flow rate x Operating hours/1000. Resin Volume= Cation load/ (Exchange capacity x Correction factor). Resin Volume =[(80 x 135 x 20)/1000]/(47 x 0.9)= 4.8 m3.
15. Calculate the amount of resin required for the following information.
Cation Load: 100 ppm as CaCO3
Capacity: 57 Kg/m3
Correction factor: 0.9
Flow rate: 135 m3/hr
Operation hours: 20 hrs
a) 4.5 m3
b) 5.3 m3
c) 7.9 m3
d) 7.5 m3
Answer: b
Clarification: Cation load= Cation as CaCO3 x Flow rate x Operating hours/1000. Resin Volume= Cation load/ (Exchange capacity x Correction factor). Resin Volume =[(100 x 135 x 20)/1000]/(57 x 0.9)= 5.3 m3.
16. Calculate the SAC resin required for the following data. It should be noted that prior to the SAC, a WAC system is present.
M Alkalinity: 100 ppm as CaCO3
P Alkalinity: 100 ppm as CaCO3
EMA: 50 ppm as CaCO3
Capacity: 57 Kg/m3
Correction factor: 0.9
Flow rate: 135 m3/hr
Operation hours: 20 hrs
a) 4.5 m3
b) 6.9 m3
c) 5.7 m3
d) 7.5 m3
Answer: b
Clarification: The WAC removes 60 % of the load of the Alkalinity. The load for SAC is calculated as 0.4 x (P Alkalinity + M Alkalinity). Ionic load= 0.4 x (P Alkalinity + M Alkalinity) +(EMA) as CaCO3 x Flow rate x Operating hours/1000. Resin Volume= Cation load/ (Exchange capacity x Correction factor). Resin Volume = [(130 x 135 x 20)/1000]/(57 x 0.9)= 0.6 m3.
17. The treatment system consists of a WAC, SAC which is followed by a WBA and SBA. Calculate the amount of WBA resin required for the following data.
M Alkalinity: 100 ppm as CaCO3
P Alkalinity: 100 ppm as CaCO3
EMA: 25 ppm as CaCO3
Capacity: 37 Kg/m3
Correction factor: 0.9
Flow rate: 135 m3/hr
Operation hours: 20 hrs
a) 2.5 m3
b) 2.8 m3
c) 1.2 m3
d) 7.5 m3
Answer: c
Clarification: The SAC removes around 60% of the EMA. WBA removes only EMA. Ionic load= 0.4 x EMA as CaCO3 x Flow rate x Operating hours/1000. Resin Volume= Anion load/ (Exchange capacity x Correction factor). Resin Volume = [(15 x 135 x 20)/1000]/(37 x 0.9)= 1.2 m3.
18. The treatment system includes a WAC, SAC, followed by a WBA and SBA. There is no degasser in this system. Calculate the amount of resin required for the following information.
M Alkalinity: 100 ppm as CaCO3
P Alkalinity: 100 ppm as CaCO3
Silica: 45 ppm as CaCO3
CO2: 45 ppm as CaCO3
Capacity: 37 Kg/m3
Correction factor: 0.9
Flow rate: 35 m3/hr
Operation hours: 10 hrs
a) 1.5 m3
b) 1.1 m3
c) 7.9 m3
d) 7.5 m3
Answer: b
Clarification: SBA removes Silica, carbon dioxide and Alkalinity. The load for SBA is considered as CO2 as CaCO3 + Silica as CaCO3 + 5% of (M Alkalinity +P Alkalinity) + 5% EMA. Ionic load= Anion as CaCO3 x Flow rate x Operating hours/1000. Resin Volume= Anion load/ (Exchange capacity x Correction factor). Resin Volume = [(100 x 35 x 10)/1000]/(37 x 0.9)= 1.1 m3.
19. The treatment system includes a WAC, SAC, followed by a WBA and SBA. There is a degasser in this system. Calculate the amount of SBA resin required for the following data.
M Alkalinity: 100 ppm as CaCO3
P Alkalinity: 100 ppm as CaCO3
Silica: 30 ppm as CaCO3
CO2: 45 ppm as CaCO3
EMA: 100 ppm as CaCO3
Capacity: 37 Kg/m3
Correction factor: 0.9
Flow rate: 35 m3/hr
Operation hours: 10 hrs
a) 0.5 m3
b) 0.9 m3
c) 1.9 m3
d) 1.5 m3
Answer: a
Clarification: SBA removes Silica, carbon dioxide and Alkalinity. The load for SBA which have adegasser prior to it, is considered as CO2 (5 ppm –residual Carbon dioxide) as CaCO3 + Silica as CaCO3 + 5% EMA. Ionic load= Anion as CaCO3 x Flow rate x Operating hours/1000. Resin Volume = Anion load / (Exchange capacity x Correction factor). Resin Volume = [(40 x 35 x 10)/1000]/(37 x 0.9)= 0.5 m3.