Answers to these questions appear at www.watertechonline.com/certification-action-line.
Certification Action Line features questions and answers typical of those appearing in Water Quality Association (WQA) certification examinations. Some answers may not satisfy everyone or every condition.
1. Dilution of brine to the 10 to 12 percent concentration range in water softener regeneration provides:
a) reduced osmotic shock in the resin
b) better resin life
c) sufficient volume of brine solution so as to uniformly contact all of the resin
d) a and b
e) all of the above
2. Displacement (slow) rinse flow rates following brine draw in water softener regeneration should be maintained at less than 0.25 gallons per minute per cubic foot of resin to ensure the desired 30 minutes of brine contact time with the resin.
3. When the sodium chloride concentration in brine drops below 8 percent, the driving force to displace hardness on softening resin with sodium is lowered. This causes:
a) higher hardness leakage during the service cycles
b) drop-off in hardness exchange capacity of the resin bed
c) higher regeneration efficiency
d) a and b
e) all of the above
4. With the use of seawater (2.5 percent to 2.75 percent NaCl concentration) to regenerate an ion exchange water softener, the hardness exchange capacity obtained is about ______ of the capacity that could be obtained by the use of 10 percent low hardness brine.
a) 90 percent
b) 75 percent
c) 65 percent
d) 50 percent
e) 25 percent
5. The hardness exchange capacity of regenerated softening resins varies with the amount of salt used in regeneration. Eight percent polystyrene divinylbenzene resin can be regenerated with 15 pounds of salt per cubic foot of resin, for example, to develop about 31,000 grains of hardness exchange capacity per cubic foot of resin. At six pounds of salt per cubic foot of resin, the maximum exchange capacity drops to about which of the following?
a) 18,000 grains/ft3
b) 21,000 grains/ft3
c) 25,000 grains/ft3
d) 28,000 grains/ft3
6. The maximum salt efficiency, in terms of grains of hardness exchange per pound of salt used, obtained with six pounds of salt per cubic foot of resin in eight percent polystyrene divinylbenzene softening resin is about:
a) 3,500 grains per pound
b) 3,350 grains per pound
c) 4,000 grains per pound
d) 3,000 grains per pound
7. Cation exchange resin is regenerated to the sodium (Na+) form with salt (NaCl). What must be used to regenerate cation exchange resin to the hydrogen (H+) form?
b) hydrogen gas
8. An advantage of hydrochloric acid in regenerating or cleaning cation exchange resin is that it is:
a) less expensive than sulfuric acid
b) no cations expected to be found in water supplies form insoluble precipitates with HCl
c) HCl does not generate heat when it is added to water
d) all of the above
9. When diluting an acid, you should never add water to an acid.
10. Nitric acid is a generally acceptable choice for acid regeneration of cation exchange resins.