596 Fermentation and Biochemical Engineering Handbook 7.0 WATER SOFTENING Water is softened to remove the scale-forming hardness elements Soft water is required for boilers, water heaters, cooling towers, reverse osmosis systems, etc. Softening is an ion-exchange process which replaces almost all of the metallic or cations by sodium ions and sometimes, the anions with chlorine ions. Therefore, a constant supply of salt is required a softener may be used in conjunction with a deionizer on certain water supplies to provide softened water for use in regeneration. This will prevent the formation of insoluble precipitates within the deionizer resin bed It is important to note that softening does not remove silica, which forms a very hard scale that is not easily removed In addition, softening does not remove chloride which can cause stress corrosion cracking in stainless A freshly regenerated resin bed is in the sodium(Na)form. When in service, sodium cations are exchanged for undesirable quantities of calcium(Ca*), magnesium (Mg*), and iron(Fe)ions. Sodium ions already present in the raw water pass through the process unchanged. Upon exhaustion of the resin, as indicated by unacceptable hardness leakage, most systems are designed to go automatically into regeneration. It should be noted that although the water is softened, the total dissolved solids content remains unchanged. Further, the effluent contains the same anions as the supply water. Softeners can be a microbial concern. a dark and moist column interior can provide a growth environment. The regeneration cycle which uses concentrated brine solution and a backwash cycle aids in reducing the bioburden. Softeners should be regenerated based on a time clock set for twice weekly regenerations and on a volumetric flow of water, whichever is shorter. Since the regeneration cycle removes the softener bed from opera tion,a dual bed system is often specified 8.0 ACTIVATED CARBON Activated carbon has long been used as an effective means of removing organics, chlorine, chlorates, other chlorine compounds and objec tionable tastes and odors. The organics removed include pesticides, herbi- cides and industrial solvents for which activated carbon has diverse capacity Typically, carbon filters are operated at a flow rate of 1-2 gpm/ft'ofactivated carbon596 Fermentation and Biochemical Engineering Handbook 7.0 WATER SOFTENING Water is softened to remove the scale-forming hardness elements. Soft water is required for boilers, water heaters, cooling towers, reverse osmosis systems, etc. Softening is an ion-exchange process which replaces almost all ofthe metallic or cations by sodium ions and sometimes, the anions with chlorine ions. Therefore, a constant supply of salt is required. A softener may be used in conjunction with a deionizer on certain water supplies to provide softened water for use in regeneration. This will prevent the formation of insoluble precipitates within the deionizer resin bed. It is important to note that softening does not remove silica, which forms a very hard scale that is not easily removed. In addition, softening does not remove chloride which can cause stress corrosion cracking in stainless steel. A freshly regenerated resin bed is in the sodium @a+) form. When in service, sodium cations are exchanged for undesirable quantities of calcium (Ca++), magnesium (Mg++), and iron (Few) ions. Sodium ions already present in the raw water pass through the process unchanged. Upon exhaustion ofthe resin, as indicated by unacceptable hardness leakage, most systems are designed to go automatically into regeneration. It should be noted that although the water is softened, the total dissolved solids content remains unchanged. Further, the effluent contains the same anions as the supp 1 y water. Softeners can be a microbial concern. A dark and moist column interior can provide a growth environment. The regeneration cycle which uses concentrated brine solution and a backwash cycle aids in reducing the bioburden. Softeners should be regenerated based on a time clock set for twice weekly regenerations and on a volumetric flow of water, whichever is shorter. Since the regeneration cycle removes the softener bed from opera￾tion, a dual bed system is often specified. 8.0 ACTIVATED CARBON Activated carbon has long been used as an effective means of removing organics, chlorine, chlorates, other chlorine compounds and objec￾tionable tastes and odors. The organics removed include pesticides, herbi￾cides and industrial solvents for which activated carbon has diverse capacity. Typically, carbon filters are operated at a flow rate of 1-2 gpm/ft3 of activated carbon