Test 10 - Water Softening and Process Design

Question 1 ప్రశ్న 1

What is meant by total hardness of water in conventional water-treatment calculations?

A The combined calcium and magnesium hardness, conventionally expressed as an equivalent concentration of CaCO3 B Only the concentration of bicarbonate ions C The sum of all dissolved solids irrespective of ion type D The concentration of chloride plus sulphate only

Question 2 ప్రశ్న 2

Under the currently applicable IS 10500 drinking-water specification, what are the acceptable and permissible limits in the absence of an alternate source for total hardness as CaCO3?

A 100 and 200 mg/L B 150 and 300 mg/L C 200 and 600 mg/L D 500 and 2000 mg/L

Question 3 ప్రశ్న 3

According to current MoHUA/CPHEEO guidance, how is water having a total hardness of 220 mg/L as CaCO3 classified?

A Soft B Moderately hard C Hard D Very hard

Question 4 ప్రశ్న 4

Which statement is consistent with current CPHEEO guidance regarding domestic softening need?

A Softening is always mandatory whenever any calcium is present B When hardness is below about 150 mg/L as CaCO3, softening for domestic purposes is not usually required C All water above 50 mg/L hardness must be softened to zero hardness D Domestic softening is determined only by chloride concentration

Question 5 ప్రశ్న 5

When total hardness and total alkalinity are both expressed as CaCO3, which relation is conventionally used to separate carbonate and non-carbonate hardness?

A Carbonate hardness is the smaller of total hardness and total alkalinity; non-carbonate hardness is total hardness minus carbonate hardness B Carbonate hardness is always twice the alkalinity C Non-carbonate hardness is always equal to total alkalinity D Carbonate hardness is total hardness plus alkalinity

Question 6 ప్రశ్న 6

A water has total hardness of 320 mg/L as CaCO3 and total alkalinity of 180 mg/L as CaCO3. What are its carbonate hardness and non-carbonate hardness?

A 140 and 180 mg/L respectively B 180 and 140 mg/L respectively C 320 and 0 mg/L respectively D 180 and 320 mg/L respectively

Question 7 ప్రశ్న 7

A water sample contains 40 mg/L of calcium ion. Using an equivalent weight of 20 for Ca2+, what calcium hardness is this equivalent to as CaCO3?

A 40 mg/L B 80 mg/L C 100 mg/L D 200 mg/L

Question 8 ప్రశ్న 8

A water sample contains 24 mg/L of magnesium ion. Using an equivalent weight of 12 for Mg2+, what magnesium hardness is this equivalent to as CaCO3?

A 50 mg/L B 75 mg/L C 100 mg/L D 120 mg/L

Question 9 ప్రశ్న 9

A water contains 48 mg/L Ca2+ and 24 mg/L Mg2+. Using equivalent weights of 20 and 12 respectively, what are the total hardness and its CPHEEO hardness classification?

A 120 mg/L as CaCO3, moderately hard B 180 mg/L as CaCO3, hard C 220 mg/L as CaCO3, hard D 320 mg/L as CaCO3, very hard

Question 10 ప్రశ్న 10

Which statement best describes the basic removal mechanism of lime-soda softening?

A Calcium is precipitated principally as CaCO3 and magnesium as Mg(OH)2 after suitable lime and soda addition B Calcium and magnesium are converted entirely into dissolved sodium chloride C Hardness is removed only by membrane evaporation D Lime-soda treatment merely measures hardness without changing it

Question 11 ప్రశ్న 11

For a lime-soda calculation, a water contains 120 mg/L calcium carbonate hardness, 60 mg/L magnesium carbonate hardness, 80 mg/L calcium non-carbonate hardness and 40 mg/L magnesium non-carbonate hardness, all expressed as CaCO3. Neglect CO2, acidity and other chemical demands. What are the theoretical requirements of pure Ca(OH)2 and pure Na2CO3?

A Ca(OH)2 = 127.2 mg/L and Na2CO3 = 207.2 mg/L B Ca(OH)2 = 207.2 mg/L and Na2CO3 = 127.2 mg/L C Ca(OH)2 = 280 mg/L and Na2CO3 = 120 mg/L D Ca(OH)2 = 120 mg/L and Na2CO3 = 80 mg/L

Question 12 ప్రశ్న 12

A 12 MLD plant treats the water in the previous question using theoretical doses of 207.2 mg/L Ca(OH)2 and 127.2 mg/L Na2CO3. What pure chemical quantities are required per day?

A 2,486.4 kg/day Ca(OH)2 and 1,526.4 kg/day Na2CO3 B 207.2 kg/day Ca(OH)2 and 127.2 kg/day Na2CO3 C 1,526.4 kg/day Ca(OH)2 and 2,486.4 kg/day Na2CO3 D 24,864 kg/day Ca(OH)2 and 15,264 kg/day Na2CO3

Question 13 ప్రశ్న 13

If the lime requirement is 2,486.4 kg/day of pure Ca(OH)2 and the commercial lime is 90% pure, while the soda requirement is 1,526.4 kg/day of pure Na2CO3 and commercial soda ash is 95% pure, what commercial masses are approximately required?

A 2,238 kg/day lime and 1,450 kg/day soda B 2,762.7 kg/day lime and 1,606.7 kg/day soda C 2,486.4 kg/day lime and 1,526.4 kg/day soda D 3,315 kg/day lime and 2,104 kg/day soda

Question 14 ప్రశ్న 14

Why does magnesium carbonate hardness require twice the lime equivalent used for calcium carbonate hardness in the conventional stoichiometric lime-soda calculation?

A One lime equivalent converts bicarbonate alkalinity and an additional lime equivalent supplies hydroxide needed to precipitate magnesium as Mg(OH)2 B Magnesium has no reaction with lime, so the factor is arbitrary C Two lime equivalents are required only to increase chloride concentration D The factor is used because magnesium hardness is actually dissolved oxygen

Question 15 ప్రశ్న 15

Which statement correctly describes the practical residual-hardness limitation of lime-soda softening under current CPHEEO guidance?

A It can routinely produce absolutely zero hardness B It should not be expected to reduce hardness below about 40 mg/L as CaCO3, whereas ion exchange can produce zero-hardness water C It cannot reduce hardness below 600 mg/L D It always leaves exactly 200 mg/L hardness

Question 16 ప్రశ్న 16

What is the principal purpose of recarbonation following lime or lime-soda softening?

A To add CO2 so that excessive alkalinity and pH are reduced and the softened water is stabilized against undesirable calcium-carbonate precipitation B To increase hardness to its original value deliberately C To regenerate a sodium zeolite bed D To oxidize chloride into chlorine gas

Question 17 ప్రశ్న 17

What is the fundamental softening mechanism in the sodium-zeolite process?

A Calcium and magnesium ions in the water are exchanged for sodium ions held by the zeolite B Calcium and magnesium are evaporated from the water C Hardness is destroyed by ultraviolet radiation D All dissolved ions are precipitated as aluminium hydroxide

Question 18 ప్రశ్న 18

How is an exhausted sodium-zeolite softening bed normally regenerated?

A By passing a concentrated sodium chloride solution through the bed B By adding alum to the bed C By heating the bed to boiling temperature D By applying chlorine gas until calcium evaporates

Question 19 ప్రశ్న 19

Which statement about total dissolved solids during sodium-cycle zeolite softening is most accurate?

A The process substantially removes all dissolved salts and therefore always reduces TDS to nearly zero B It principally exchanges Ca2+ and Mg2+ for Na+ and therefore does not constitute general demineralization or major TDS removal C It removes only suspended sand and has no effect on hardness D It converts all sodium into insoluble calcium carbonate

Question 20 ప్రశ్న 20

Which statement correctly describes the sodium and hydrogen cycles of ion-exchange softening?

A The sodium cycle releases Na+ and is regenerated with NaCl, while a hydrogen-cycle cation exchanger releases H+ and is regenerated with acid B Both cycles are regenerated only with chlorine gas C The sodium cycle releases calcium and the hydrogen cycle releases magnesium D Neither process is reversible

Question 21 ప్రశ్న 21

A raw water has total hardness above 700 mg/L as CaCO3 and also contains significant turbidity, colour and iron. Which treatment selection is most consistent with current CPHEEO guidance?

A Lime-soda softening may be particularly suitable because the precipitation process can handle very high hardness and the turbidity, colour and iron would tend to foul or coat an ion-exchange bed B Untreated sodium-zeolite softening is always mandatory regardless of turbidity and iron C No softening should ever be considered above 600 mg/L D Only chlorination is required because hardness is bacteriological

Question 22 ప్రశ్న 22

A zero-hardness ion-exchange effluent is blended with untreated water having hardness 300 mg/L as CaCO3. What blend of untreated and softened water will produce a final hardness of 90 mg/L, assuming linear mixing and no other hardness source?

A 10% untreated and 90% softened B 30% untreated and 70% softened C 50% untreated and 50% softened D 70% untreated and 30% softened

Question 23 ప్రశ్న 23

An ion-exchange bed has a usable hardness-removal capacity equivalent to 50 kg of CaCO3 before regeneration. If the incoming water hardness is 250 mg/L as CaCO3 and complete hardness removal is assumed, what water volume can be treated before the stated capacity is exhausted?

A 20 m3 B 50 m3 C 200 m3 D 500 m3

Question 24 ప్రశ్న 24

Why does magnesium non-carbonate hardness consume both lime and soda ash in a conventional lime-soda calculation?

A Lime precipitates magnesium as Mg(OH)2 but produces an equivalent calcium non-carbonate salt, which then requires soda ash to precipitate the calcium as CaCO3 B Magnesium non-carbonate hardness does not react with either chemical C Soda ash is required only to disinfect the water D Lime converts magnesium directly into sodium without producing any calcium species

Question 25 ప్రశ్న 25

Consider the following statements about water softening: I. Carbonate hardness is limited by alkalinity when hardness and alkalinity are expressed as CaCO3. II. Lime-soda treatment removes calcium principally as CaCO3 and magnesium principally as Mg(OH)2. III. Sodium zeolite exchanges Ca2+ and Mg2+ for Na+ and is regenerated with brine. IV. Current CPHEEO guidance states that lime-soda softening cannot practically produce zero-hardness water, whereas ion exchange can. Which option is correct?

A I and II only B I, II and III only C II, III and IV only D I, II, III and IV

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