Softener Equipment

Sodium zeolite softener systems consist of a softener tank, valving and a means of transporting brine (salt solution) to the softener tank.  The tank includes a service and rinse water inlet distributor, freeboard or the headspace from the top of the resin bed to the top of the vertical wall of the tank, a regenerant distributor, a bed of ion exchange resin and sometimes a supporting medium or outlet distribution system.

The inlet assembly is designed to evenly distribute the incoming water.  It also acts as a collector for the backwash water that goes to the sewer.

The feedboard space allows the resin to expand without loss to drain during the backwashing.  It should be designed to permit a minimum of 50% expansion.

The regenerant distributor located above the resin bed, spreads the brine uniformly over the resin beads.

A bed of resin, operating in the sodium cycle, softens the water.  The quantity of resin used depends on the raw water hardness, the quantity of water to be treated per regeneration, flowrate, and the regenerant level employed.

An underdrain system evenly collects the treated water, waste brine and rinse water, and distributes the backwash water.

It is not unusual to have a valving system that consists of either a valve nest or a single, multiport control valve.  A nest of six (6) main valves is needed for the service inlet and outlet, backwash inlet and outlet, brine inlet and rinse outlet.  The valves may be either manually operated or any variety of air-, water- or motor-operated automatic valves.  A single, multiport control valve may be used in place of the valve nest.  As the multiport valve moves through a series of four positions, the ports in the valve direct the flow of water in the same manner as the opening and closing of separate valves.

The brining system consists of a salt dissolving/brine – measuring tank.  It is used to prepare a saturated brine solution.  This tank frequently has a float – operated valve to control the fill and drawdown level and thus, the quantity of brine added to the softener.  Usually an eductor transfers the saturated brine to the softener and dilutes the saturated brine with inlet water to the desired concentration for resin regeneration.

A future article will include a guide to softener troubleshooting along with additional information on softener operation and maintenance.

Softener Operation and Regeneration

Softener Operation

A sodium zeolite softener operates through two basis cycles:  the service cycle, which produces soft water, and the regeneration cycle, which restores the exhausted resin to capacity.  During the service cycle, raw water enters the softener through the inlet distributor, flows through the resin bed, is collected by the underdrain system and then transferred to the point of use.

When a softener is exhausted, it must be regenerated.  A number of methods may be used to signal the need for regeneration.  Many facilities rely on operator testing to determine when hardness breaks through.  Another common method for determining when regeneration is needed is to measure the quantity of water treated between regenerations.  A water meter in the service water line is used to sound an alarm or automatically initiate regeneration when a preset number of gallons has been softened.

Softener Regeneration

As we have said, regeneration is the process by which the resin is exposed to a strong concentration of highly ionizable material, such as salt.  While the resin has a greater affinity for calcium and magnesium than for sodium, the high concentration of the regenerant forces the ions on the bead into solution and substitutes the sodium ion.  This process is called elution.  The concentration of the regenerant is a critical factor in all ion exchange.  Softener regeneration generally consists of four (4) steps:

  1. Backwash
  2. Brining
  3. Slow Rinse
  4. Fast Rinse


Backwashing is an upward flow of water which lifts and expands the resin bed.  It removes the accumulation of particulates (entering via raw water) and resin fines (broken pieces of resin).


The brine regenerant stream enters the softener, flows downward through the resin bed and then is discharged to waste.

Slow Rinse:

A low flow rate of rinse water follows the regenerant to displace the brine downward through the resin bed while slowly rinsing the unit.  The flow rate for this slow rinse step is the same as the flow rate for the brining step.

 Fast Rinse:

A high flow of rinse water follows the slow rinse procedure to remove residual brine from the resin bed.  The flow rate for the fast rinse step is identical to the flow rate while the softener is in the service cycle.

Usually a unit can return to service as soon as the hardness value reaches the desired preset level, but some operators continue to rinse until chlorides are reduced to a value near that of the influent level.

Again, the frequency at which any resin must be regenerated is a function of:

  1. The volume of water treated.
  2. The concentration of exchangeable ions in the water.
  3. The type of resin.
  4. The amount of resin present.
  5. The type of regenerant.
  6. The amount of regenerant.


Principles of Zeolite Softening

Principles of Zeolite Softening

Sodium zeolite softeners use exchange resins made of polystyrene.  These resins have sodium ions loosely attached and will readily give up sodium for more desirable ions such as calcium and magnesium.  This exchange is only for cations (positively charged ions).  This is why sodium zeolite resin is referred to as a cation exchange resin (Figure 2).


Figure 2 – Sodium zeolite resin gives up sodium ions for calcium and magnesium

The water to be softened passes through the vessel containing resin.  Calcium and magnesium ions are exchanged for the sodium ions in and on the resin beads.  The sodium then takes the place of the calcium and magnesium with the appropriate anion (negative component).

A plot of the softener effluent profile shows a low, nearly constant effluent hardness level until the ion exchange resin nears exhaustion.  At this point, the hardness level usually increases quite rapidly and regeneration is required (Figure 3).

Figure 3 – As the resin nears exhaustion, the hardness level increases rapidly.

Regeneration is achieved by reversing the softening reactions.  Exhausted resin is exposed to a concentrated solution of sodium chloride.

Normally, zeolite resin more readily releases sodium in exchange for calcium and magnesium.  However, with the high concentration of sodium in the brine, the sodium ions displace the calcium and magnesium ions attached to the beads.  Thus, the high concentration of salt in the regenerant supplies the driving force to replace the hardness cations.  The calcium and magnesium are removed from the softening unit through the wave brine and rinse streams.

The frequency of regeneration needed depends on the rate or quantity of water, the calcium and magnesium content of the raw water, the quantity of exchange resin in the softener and the amount of salt used per regeneration.  The operating plant usually controls only the flow and the amount of regenerant.  The other parameters are fixed by the system design and the raw water hardness level

Softener Application and Ion Exchange

Softener Application

The potential for scale and deposit buildup exists in every raw water supply.  The ability of the sodium zeolite softener to reduce this potential effectively and economically makes this an ideal pretreatment for boiler feedwater and many types of chemical process waters.  Compared to other softening methods, sodium zeolite units offer many advantages:

  1. The treated water has a very low scaling tendency because this method reduces the hardness level of most water supplies to less than one part per million (ppm).
  2. Operation is simple and reliable; automatic regeneration controls are available at a reasonable cost.
  3. Regeneration is accomplished with inexpensive, easy-to-handle salt (NaCl).
  4. Waste disposal usually presents no problem.
  5. Within limits, variations in the water flow rate have little effect on the treated water quality.
  6. Efficient operation can be obtained in almost any size unit, making sodium zeolite softeners suitable for both large and small installations.

The Ion Exchange Process

Ion exchange is the process in which materials exchange one ion for another, hold it temporarily, and release it to a regenerating solution.  These materials are widely used to treat raw water supplies which contain dissolved salts.  Today the most commonly used material is an ion exchange resin.  Resins are plastic beads to which a specific ion has been attached – an ion which is exchanged for other ions in the water supply (Figure 1).  Once the resin has given up or exchanged most of its exchangeable ions, it is said to be exhausted and needs to be regenerated by coming in contact with a strong solution of ions called the regenerate.  The regeneration procedure will be explained in detail later in this article.

Softener Operation and Troubleshooting

Good water softener operation is often a key factor in efficient boiler system performance.  In its simplest terms, softening is the removal of naturally occurring scale-forming ions that are present in all water irrespective of its source.  Although we take it for granted, the operation of a water softener is really a remarkable phenomenon.  As you can see in the example below – a properly functioning can, in fact, remove thousands of pounds of potentially costly calcium and magnesium (hardness) from boiler water.

The whole softening process is based on ion exchange – the means by which sodium ions in the softener resin are exchanged for calcium and magnesium ions.  The beauty of all this is that the process is reversible.  Once the softener resin has given up its sodium ions in exchange got hardness ions, the resin can be regenerated to begin its work all over again.

The ion exchange process has evolved from its discovery in England around 1850, through the development of natural and synthetic exchange materials called zeolites (a name that stuck), to today’s complex ion exchange resins consisting of hydrocarbon networks to which ionizable functional groups are attached.

Understanding the sophisticated physical chemistry of the ion exchange process is not our goal here.  Our real objective is a basic understanding of how the system is supposed to work and how a smoothly running softener can help overall boiler operation.

Wait… Water has a 2nd Liquid State?

By Luke Wonnell

If you’re like me then you remember learning in High School chemistry or pre-req college courses that water has 3 states: solid, liquid and gas right? Water becomes solid ice below 32⁰F, exists as a liquid between 33⁰F and 212⁰F and starts to boil off to a gas at 212⁰F. While these critical points remain, it turns out the liquid state may be a lot more complex than we originally thought.  A little over a year ago, an international team of scientists and physicians made an incredible discovery – water may very well have a 2nd liquid state!  What the what… how was this not major news?

As this team was conducting their experiments, they discovered remarkable changes to the physical properties of liquid water when heated between 40⁰C and 60⁰C (104⁰F and 140⁰F). When the “crossover temperatures” were reached, the researches noticed significant changes to the thermal conductivity, electrical conductivity and surface tension of the water in addition to several other physical properties.

I say “crossover temperatures” as plural because each physical property changed at different temperatures!  For example, the crossover temperature for thermal conductivity was 64⁰C (147⁰F), whereas the crossover temperature for surface tension was 57⁰C (134.6⁰F) and the crossover temperature for electrical conductivity was 53⁰C (127⁰F)… mind blown!

There’s still a lot of work to be done to understand the full impact of this discovery, but just think about what effects this might have on a typical condensing boiler system or domestic hot water system because these “crossover temperatures” are within the appliance’s normal operating range:

  • The Good: Increased thermal conductivity would mean the boiler or water heater is able to transfer the heat of combustion into the water more efficiently.
  • The Bad: Increased electrical conductivity could accelerate the effects of Galvanic corrosion since the water is able to more efficiently facilitate the flow of electrons.
  • Higher surface tension might require more pump horsepower to flow the same amount of water and make Oxygen elimination less effective.



Biofilm Control

Presence of the Legionella organism in water systems can often be associated with the presence of biofilm.  Biofilm is a sticky substance which forms under the right conditions, often appearing as slime.  It attaches to piping and component surfaces, and provides the ideal environment for a community of organisms, including Legionella, to live and thrive.  Therefore, controlling biofilm is an integral part of controlling Legionella, and its removal is essential to achieving a proper state of water system cleanliness.  Biofilm control should be part of every Water Management plan. 

 Many have wondered whether conventional oxidizing treatments are capable of successfully eradicating biofilm on their own.  Chlorine for example, will only burn away surface layers of biofilm.   In the process it is readily consumed, and often requires very high concentrations to have any productive effect.  It is very corrosive even at low levels, and much more aggressive at elevated concentrations.  Chlorine alone lacks the punch necessary to penetrate and break apart a slime matrix.   Because of these limitations, when heavy biofilm is confirmed, we act to augment conventional chemical cleaning protocols with a separate dose of Chlorine Dioxide.  As a gas in water, Chlorine Dioxide is fully capable penetrating biofilms, breaking and sloughing them into the bulk water for their removal by mechanical means and for the parallel disinfection of those released active micro-organisms.  Chlorine Dioxide is a weak oxidizer that is not corrosive, and is not affected by pH conditions.  The key to using the tool is to produce it safely, conveniently, and to have it readily available when test results warrant. 

 The Metro team has an integrated set of solutions to deal with all water system challenges, including the use of this very effective tool against biofilm.  When you have a tough challenge, be sure to ask about chlorine dioxide supported cleaning platforms. 

Written by:

John D. Caloritis, CWT, Technology Director The Metro Group, Inc.

Legionella & Water Management Webinar Recap

On Tuesday, December 5th, The Metro Group, Inc. hosted its first of many upcoming webinars that will be discussing and educating on subjects relating to Water Treatment, Water Management, and Boiler/Burner Efficiency Testing and Care. This particular webinar titled “Legionella & Water Management and Real-World Experience for Building Water Management Plans,” was a free webinar training that focused on the Do’s and Don’ts of putting together a Water Management Plan to reduce the risk of Legionella in facility water systems, based on the real-world experience of Metro’s water treatment professionals. The seminar was designed for the building personnel responsible for creating and implementing plans. Afterwards, the attendees left the webinar with an understanding of what a Water Management Plan is, where and how to get started with one, and how to stay in compliance with the various regulations and mandates, including the CMS policy for the Healthcare Industry and the New York State legislation for Cooling Towers and Potable Water Systems.

The webinar lasted about 45 minutes with time for a helpful Q&A to end the presentation. Overall, the high turnout and positive feedback will be useful for conducting webinars in the future. If you are interested in attending this webinar, an encore presentation will be held on December 21st from 2:00pm-3:00 pm EST.

 Who should attend?

• Building Owners & Agents • Facilities & Maintenance • Infection Control & EHS • Engineering & Operations Agenda: • Brief overview of Legionella • Building Water Systems at Risk • Water Management Plan’s, Defined • Current Legislation & Guidelines

Register at the link below:

Or visit our site to join our mailing list and keep up with any and all upcoming webinars:


Recent Legionnaires’ Outbreaks

There is growing awareness, publicity and liability due to high profile legionella outbreaks.
Contact us to make sure your facility as a Water Management in place to reduce your likelihood of risk and liability.
Five Recent Legionnaires’ Disease Outbreaks:
1. Hospital plumbing system implicated in 46 cases, including 4 deaths. Forty-Six Legionella infections have been diagnosed among patients of a hospital in the Lisbon area of Portugal since October 31. Four of the patients have died. Portuguese health officials suspect the source of the outbreak was the hospital’s domestic (potable) plumbing system.
2. 15 Cases in Flushing, New York. Fifteen cases of Legionnaires’ disease were identified in Flushing, NY (New York City area) in October. NYC Health investigators tested several cooling towers and ordered disinfection of the ones in which Legionella was found.
3. Cases among Disneyland visitors. Twelve people who spent time in Anaheim, California in September were diagnosed with Legionnaires’ disease. After Orange County health officials saw that 9 of the 12 had visited Disneyland, the park shut down and disinfected two cooling towers. Most of the 12 who contracted the disease were hospitalized. One of the three persons who did not visit Disneyland in the days before onset of infection has died. Information about the environmental and epidemiologic investigation has not been reported.
4.Five cases at a New York City assisted living facility. Five residents of an assisted living facility in the Bronx (New York City) Riverdale neighborhood were diagnosed with Legionnaires’ disease last month. All five recovered without hospitalization. Little information about the investigation or response was found in news reports except that additional chemicals were added to the facility’s cooling towers.
5. Potting mix the suspected source of 10 cases. Ten people in Christchurch, New Zealand were hospitalized with Legionnaires’ disease earlier this month. Potting mix was reported as the suspected source. In New Zealand and Australia, Legionella longbeachae in potting mix is a major source of Legionnaires’ disease, accounting for approximately half of reported cases.