1. c. Macroreticular is synonymous with macroporous meaning large pores. Macro-reticular or macroporous ion exchange resins first were developed in the late 1950s. They use the same chemical (monomer) ingredients to make the beads of resin, except also included is a third ingredient that is soluble in the monomers, but which becomes insoluble in the resin polymer structure as it is formed. The third ingredient is then removed from the resin structure, leaving a resin bead with extra continuous pores in the gaps between the continuous resin phase, from which the third ingredient has been extracted.
2. False. Gel resins are the standard two-ingredient (styrene and divinylbenzene) resins. They are called gelular because under very high magnification they look like a slice of gelatin. The macroporous (or macroreticular) resin structure differs by being very porous, with discrete physical voids; under very high magnification it appears like bundled together microspeheres of gel resin.
8. c. A cubic foot of resin is equal to 7.5 gallons, and the void volume (the space not occupied by resin) in a packed column of resin is approximately 40 percent. Therefore, the total water in contact with that cubic foot of resin at any one time would be: 7.5 x 0.4 = three gallons.
9. a. 30-inch bed depth plus 12-inch (40 percent x 30 inches) freeboard plus six-inch underbedding equals 48 inches.
10. b. Where the resin beads interface or make contact with the distribution system in the resin tank is a significant point of water pressure drop. The beads can deform into the open spaces of the screen or slots of the distributor, thereby causing a reduction in the open area of the distributor. Most standard softening resins will cause between 0.6 and 2.0 psig water pressure drop per foot of resin bed depth at a water flow rate of eight gpm per square foot of bed surface area. In addition, the pressure drop at the resin interface with the distributor (depending on the distributor design) can be in the range of two to four psig.