HOW HOME WATER CONDITIONERS WORK
A PRIMER ON WATER SOFTENERS/CONDITIONERS
(AKA ION EXCHANGE SYSTEMS)
Note: See Glossary of Water Terms for assistance in understanding specific descriptors in this section.
As suggested by the name, water conditioners/ion exchange equipment operates by replacing certain ionized chemicals with other ionized chemicals. This process has several variations and is one of the oldest technologies utilized for water treatment/conditioning.
The basic construction of an ion exchanger is a cylinder, or pressure vessel, housing a volume of insoluble spheres or beads, termed "resin", attached to which are either anions (negatively charged ions) or cations (positively charged ions). Housed in this manner, the ion exchange media is referred to as a "resin bed".
During the exchange process, ions present in the supply water attach themselves to the resin, and doing so, displace previously attached ions into the water. A basic concept of this process is that the exchange is made only for ions of the same charge, that is, anions for anions and cations for cations.
Regardless of type, ion exchange capacity is limited by the quantity of exchangeable ions attached to a resin sphere and the volume(size in cubic feet) of the resin bed. During operation, the supply of exchangeable ions is progressively reduced. When all exchangeable ions have been utilized, the bed has reached a condition referred to as "exhaustion". Prior to exhaustion, ion exchangers should be restored; that is, the new exchangeable ions are placed on the resin by a process known as "regeneration".
During ion exchange, softeners principally retain the cations calcium and magnesium while releasing sodium. The softener ion exchange process is illustrated in the following figure.
Schematic representation of water softening process showing calcium from calcium chloride being exchanged for sodium which forms sodium chloride.
Water containing calcium and/or magnesium can form relatively hard deposits and is termed "hard water". Water which has had these chemicals replaced by sodium ion exchange is termed "soft water" and hence, the term "softener". Softeners may also remove a portion of other polyvalent cations, most notably iron and magnesium, although they are somewhat limited in this regard. Removal of iron is recommended prior to the softening process to avoid "fouling" of the resin spheres in the media tank.
During softening, sodium levels are increased in proportion to the amount of calcium and magnesium removed. The amount of sodium entering the water has important implications to final water quality and/or the performance of downstream equipment, such as reverse osmosis systems.
The following information provides examples of calculations which convert water "hardness" components, principally calcium and magnesium, usually expressed as "calcium carbonate" (CaCO3), to the more conventional metric units, which may be either equivalents (mEq/L) or mass (mg/L).
SAMPLE CALCULATION, AVOIRDUPOIS UNIT OF MEASURE
If you have a water test/assay or if you have had your water supply tested for "grains of hardness, follow the following procedure to determine how much sodium will be added to your drinking water by the softening procedure. Remember to add any additional, EXISTING sodium concentrations which may be in the tap water to this calculation.
Determine the increased concentration of sodium, both as equivalents and mass units, due to softening a water supply which contains 15 grains/gal (as calcium carbonate - CaCO3) of total hardness.
1. Convert the avoirdupois units, grains/gal (as CaCO3), to mEq/L for the univalent ion, sodium, by multiplying by 0.342.
15 grains/gal (as CaCO3) x 0.342 = 5.13 mEq/L
2. Convert the concentration of sodium from mEq/L to a metric mass concentration.
The equivalent weight of a substance is determined by dividing the molecular weight of an element by its valence. Sodium has a molecular weight of 23 and a valence of 1, and so, 23 mg of sodium is equal to 1 mEq.
5.13 mEq/L x 23 mg/mEq = 118 mg/L of sodium
What does this number mean? It means, for example, that if an individual is on a sodium restricted diet and a water softener is employed in the home, he/she is now exposed to an excessive amount of sodium in the house drinking water. The American Heart Association recommends that a maximum of 20 mg/liter of sodium be present in drinking water if an individual is on a sodium restricted diet.
In the above example, the water softener is putting 6 TIMES as much sodium into the drinking water as is recommended for sodium restricted diets.
In some instances, your water analyses may report calcium and magnesium concentrations in mass units. To estimate the added sodium burden due to softening using these test results, calcium and magnesium concentrations are first converted to equivalents. The sum of calcium and magnesium equivalents equals the concentration of sodium which will be added to the water, also as equivalents.
SAMPLE CALCULATION, METRIC UNITS OF MEASURE
Determine the increased concentration of sodium, both as equivalents and in mass units, due to softening a water supply which contains 80 mg/L of calcium and 24 mg/L of magnesium.
1. Convert the concentration of calcium from mass units to equivalents. As noted in the preceding sample calculation, equivalent weights are determined by dividing the molecular weight of an element by its valence. Calcium has a molecular weight of 40 and a valence of 2, and so, 1 mEq of calcium is equal to 20 mg.
(80 mg/L)/20 mg/mEq = 4 mEq/L of calcium
2. Convert the mass concentration of magnesium to equivalents. Magnesium has a molecular weight of 24 and a valence of 2, and so, 1 mEq of magnesium is equal to 12 mg.
(24 mg/L)/(12 mg/mEq) = 2 mEq/L of magnesium
3. Sum the equivalents of calcium and magnesium to determine the concentration of sodium which will be added, also as equivalents.
4 mEq/L + 2 mEq/L = 6 mEq/L of sodium
4. Convert the equivalents of sodium to a mass concentration. As noted in the preceding sample calculation, 23 mg of sodium is equal to 1 mEq.
6 mEq/L x 23 mg/mEq = 138 mg/L of sodium.
Therefore, if your water analysis showed laboratory test results for calcium and magnesium but not calcium carbonate, this latter procedure will produce the desired result.
To check up on the integrity of the laboratory producing the lab report, you may wish to calculate the added sodium by both of the above methods, if calcium, magnesium AND calcium carbonate are all listed. You should get the same results in both calculations.
HOW WATER SOFTENERS OPERATE
Softeners have two main modes, or cycles, of operation: service and regeneration. During the service cycle, the softener exchanges "hard" cations for sodium, causing progressive depletion of exchangeable sodium to the point of exhaustion.
The softener is then "regenerated" by perfusing the resin bed with concentrated sodium chloride solution; sodium displaces the cations previously removed from the feed water.
The regeneration process actually involves a series of steps and typically requires about 1 to 3 hours to complete depending on softener make and model. The following information is a summary of the diagrammatic descriptions available HERE.
1. During service, water flows downward through the bed, causing the resin spheres to become tightly packed. The first step of the regeneration cycle, backwash, loosens and expands the media by directing water flow upward through the resin bed.
Continued back washing cleans the resin of particles, including resin fragments or "fines", trapped in the densely packed bed during the service cycle. In addition to cleaning, the loosened condition of the resin bed promotes uniform flow of brine and rinse water during later steps of the regeneration cycle.
2. Introduction of sodium chloride, or "brining", occurs next. A brine tank containing water and sodium chloride cubes or pellets is located adjacent to the softener. The resulting solution is drawn from the brine tank by means of a venturi or "eductor" located in a control valve assembly at the top of the softener.
The volume of brine drawn and the duration of this step are individualized according to local circumstances, which include the volume and hardness of water which has passed through the softener during service, the extent to which sodium has been depleted from the resin, and the volume and configuration (height and diameter) of the resin bed.
3. Next, the softener is "slow rinsed" to remove the brine solution present in the softener at the termination of brining. Slow rinsing is typically accomplished by stopping the inflow of brine and continuing water flow in the same direction and flow rate. This process ensures that the brine will be maximally utilized while removing any excess solution from the resin bed.
4. The final step in the regeneration process is the "fast rinse". Fast rinsing completes the removal of brine from the resin bed with a brisk flow of water being maintained in the same direction as during the service cycle. Fast rinsing shortens the time needed to completely remove excess brine from the resin and also serves to flush areas in which water flow is sluggish.
TYPES OF SOFTENERS
There are two general types of softeners, portable exchange and permanent. Portable exchange softeners are provided by vendors in a fully regenerated, ready-to-use condition. When regeneration is needed, it is done by the vendor at a central facility. Portable exchange softeners offer maximum convenience, since maintenance and service are provided by the vendor.
These units are particularly well suited to mobile operations, such as acute therapy performed outside the hemodialysis facility. Portable exchange softeners are more costly to operate than permanent softeners, and are, therefore, less commonly utilized when supply water contains high levels of calcium and magnesium and/or softened water consumption rates are high.
In several areas of California, the only type of water softeners permitted are portable exchange units. The high levels of dissolved solids discharged during the regeneration cycle of the softening process goes down the sanitary drain into the community water treatment system. In many areas, the community water treatment system uses this water for irrigation purposes.
It has been determined that the large amount of dissolved solids placed into these municipal water treatment plants by permanent water softeners is slowly destroying vegetation and citrus crops. Many local communities have therefore banned the permanent softener types and local water dealers cannot sell these types to residences and must instead offer portable exchange systems.
Permanent softeners are equipped with controls and a brine tank, containing concentrated sodium chloride solution, which permits regeneration of the softener at the point of use in the customer's home. There is a wide selection of permanent softeners, varying both in size and configuration as well as controls, regeneration methods and features to inform the operator of various parameters related to softener condition.
The following figure illustrates the construction of a typical permanent softener.
The underbed media serves to distribute water during back washing. Permanent softeners are well suited to non-mobile applications in which supply water contains high levels of calcium and magnesium and/or softened water consumption rates are high.
APPLYING A WATER SOFTENER/CONDITIONER TO YOUR HOME
The most common application for softening is as a pretreatment process for other water treatment/filtration equipment, such as reverse osmosis, which may be damaged by scale deposits arising from the use of "hard" water.
The concentration of sodium introduced by softening as pretreatment for reverse osmosis should also be considered when selecting an in-home drinking water system which includes these two equipment types. This is because reverse osmosis is an incomplete purification process and, if inlet concentrations of certain ions, such as sodium, are sufficiently high, the resulting product water may be unacceptable.
For example, if the final, post softener concentration of sodium is 800 mg/L and the reverse osmosis unit only removes 90% of this ion(as when the reverse osmosis system is new or only a few months old), the resulting product water would contain 80 mg/L, which clearly exceeds the maximum sodium dosage recommended by the American Heart Association for sodium restricted diets).
In this case, the far better solution is to employ a steam distillation water purifier to produce the home drinking water. Distillation removes ALL sodium from the drinking water supply as well as destroying all micro-organisms which reverse osmosis fails to do. If these two factors are important, select a steam distillation system for your home water system instead of reverse osmosis.
HOW TO SELECT THE PROPER SIZE WATER CONDITIONER/SOFTENER
In addition to considerations of softener types, described above, appropriate selection of softeners also relies on exchange capacity and the flow rates which are required. This is of particular importance for permanent softeners, since errors made in their selection are less easily remedied
Exchange capacity ratings for softeners sold in the United States are given as "grains of hardness, as calcium carbonate.Water hardness is described in terms of "grains per gallon as calcium carbonate".
Dividing the exchange capacity of the softener by the hardness of the supply yields the maximum volume of water which may be softened. It should be noted that this calculation tends to be overly optimistic for softener capacity.
While it is theoretically possible to utilize the total exchange capacity of the softener, the amount of sodium chloride required for regeneration would be excessive and "hardness leakage" during the service cycle would be likely. A more realistic approach is to anticipate that a softener will be operated at approximately 70% of its maximum capacity.
That is, regeneration should be performed when 30% of the exchangeable sodium is still available. Operating a softener in this manner will generally be more economical in terms of sodium chloride consumption and will also minimize difficulties with hardness leakage or break-through. In some instances, softener manufacturers provide specific information on the most efficient use of sodium chloride.
Determine the volume of water which can be softened by a softener having a capacity of 48,000 grains(Fleck 5600 system described earlier on this website page) with supply water having a total hardness of 10 grains/gal (as CaCO3).
1. Assume that efficient operation allows use of 70% of maximum softener capacity.
48,000 grains x .70 = 33,600 grains
2. Divide the effective capacity (70% of maximum capacity), as determined in step 1, by the total hardness of the supply water.
33,600 grains/(10 grains/gal) = 3,360 gal
Thus, the unit should be regenerated when 3,360 gal of water have been softened.
The utility of such determinations is to establish regeneration or replacement schedules, for permanent or portable exchange units, respectively, and to avoid premature exhaustion of a softener during clinical operations.
Systems such as the Fleck 5600 described earlier on this page automatically take these factors into account.
Obviously, selecting a softener of adequate capacity requires an accurate estimate of the volume of softened water which will be consumed between permanent softener regenerations or portable unit replacements. It is suggested that such estimates be based on anticipated peak consumption, including possible expansions.
Such estimates should take into account the total consumption of softened water by downstream equipment, including reverse osmosis unit water discharged to drain as "reject" as well as that of any other equipment, such as permanent carbon filters, utilizing softened water during backwash and service rinse cycles.
Softener selection should also take into account manufacturers' minimum and maximum flow ratings. If water flows too slowly through a resin bed, "channeling" may occur. In this situation, water flow will not be evenly distributed throughout the resin bed, resulting in only a portion of the media being exposed to water flow with the remainder being bypassed.
Channeling limits utilization of the media to only that portion of the media which experiences water flow, effectively reducing exchange capacity and leading to premature exhaustion. Conversely, maximum flow ratings are used to ensure that the contact time between the water and the resin is sufficient for the ion exchange reactions to be completed, and to prevent excessive loss of pressure (pressure drop) which could adversely affect the operation of downstream equipment.
OPERATING AND MAINTAINING YOUR NEW WATER SOFTENER
Maintenance requirements for permanent softeners consist primarily of ensuring a sufficient quantity of sodium chloride in the brine tank to accomplish regeneration of the resin bed. Additionally, long-term removal of iron and/or manganese by softening may cause resin deterioration, especially if the supply water contains oxidants, such as free chlorine.
Softener manufacturers can provide information regarding the concentration limits of iron and manganese for their equipment, as well as special maintenance and regeneration procedures for such circumstances. Some manufacturers recommend placing carbon before the softener to remove oxidants which may degrade the softener resin.
Other maintenance requirements, if any, should be specified by the softener manufacturer.
The importance of the type of salt used for regeneration should not be overlooked in the operation of water softeners. Salt which is designated as "rock salt" should be avoided as it is not refined and typically contains sediments and other impurities which may impede reliable softener operation.
Refined grades of salt for softener regeneration are available as pellets or cubes which vary in size and origin. To the extent possible, manufacturers' recommendations should be followed when selecting regeneration materials as even seemingly small differences may impact on softener operation.
We highly recommend "pellet" salt as we have found it to produce a better quality of softened water as well as less dirt and grit in the salt bags, thus requiring fewer cleanings of the salt bring tank with the permanent water softener.
It should also be recognized that a variety of softener resins are available, not all of which are suitable for hemodialysis applications. Be certain to specify that only "food grade" materials are used.
Water softener monitoring consists primarily of hardness testing of effluent water and is readily accomplished using an appropriate test kit. Your local water dealer can quickly and easily perform a hardness test for both influent water(to allow you to adjust the regeneration interval properly) and the effluent water(to determine how effective the water softening process is being conducted).
Such tests also will indicate if any maintenance is required on the various valves and gaskets which over time may gradually succumb to the presence of highly salty water and require replacement.
We hope this section has been of use to you as a customer or as a dealer in helping you understand more fully the inner workings of these devices. Call us to order a specific system or to have us determine what type and size system is best suited for your individual needs.
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