Professor POU/POE – May 2012

May 10, 2012

This month”s topics: Test kits, used resin, brine injectors.

Q: We are working with the Columbian government to solve a water problem and we need a field test kit for testing bacteria. Can you refer us to a source? Regards and thanks for your help.

— Bogota, Columbia

A: You did not specify which bacteria you are trying to detect but there are a few test kit manufacturers that sell bacteria test kits. Hach Company and LaMotte Company are two that I know of. You may be able to find more by using an Internet search. First, try to determine which bacteria you are looking for.

Q: I was wondering, when using ion exchange resin, what are the practical differences between using “new” or “virgin” ion exchange resin vs. “regenerated” resin? I understand there is quite a cost difference. It seems some companies insist on using only new resin. Also, does the older (regenerated) resin keep some of the contaminants that are supposed to be removed during the regeneration process or is there less capacity due to the deterioration of the resin beads?

– Washington

A: I can”t think of a worse mistake to make than to use used resin, under any circumstances. Used resin (I guess someone is calling it by the deceptive name of “regenerated” resin), has several serious drawbacks.

Physically, the bead size of the resin could be severely reduced due to the friction, which comes with age and from wear during the regeneration process. The result is that much of the resin will be rinsed to the drain the first time you properly backwash it. This is because it”s too “fine” and lightweight. If not immediately, it will happen soon.

Next, if the resin has been used on municipal water, it will be degraded from the chlorine. Chlorine reacts with the (DVB) divinylbenzene (the “glue” that holds the resin together). This causes the resin to “fall apart” in such a way that the resin beads do not remain spherical. The result is that they break apart and eventually become a resinous “mush.” It then is not a bed of beads which have space or voids between them. With the voids being lost the pressure drop through the bed severely increases. Along with this the resin beads swell to the point where the depth of the resin bed increases.

Many are deceived by this because the bed depth looks very good (too good). At this point you may be buying a cubic foot of resin which, in reality, used to be two-thirds of a cubic foot. The truth is that the resin beads are breaking down, swelling and are about to completely break apart. So far, the resin”s capacity is normal. Soon after, the beads become “fines” and are subsequently backwashed out to the drain.

Since you don”t know what type of water the resin was used on, it could have picked up heavy metals, which may still be present. Worse yet, the resin may have been used in a plating facility wherein the metals might be very concentrated.

Another possible scenario would be if the resin had been used to remove radium or barium. It is very good in this application but the resin may still contain radioactive radium, which will eventually be released into the treated water. The radium is not always removed from the resin during regeneration.

New resin has a capacity of close to 60,000 grains (hardness removal) of capacity per cubic foot. When put into use it is not economical to attempt to recover or to utilize all this capacity so we usually regenerate it to achieve a capacity range of 5,000 to 30,000 grains. The capacity of used resin is completely unknown. Without a resin analysis you have no idea how much can be recovered.

As you can understand, I am strongly suggesting that you don”t even consider buying used resin. Not only would you be using a somewhat deceptive practice, you would be selling a product that probably will not perform satisfactorily. The resin might, at best, manifest very poor performance and capacity. At the worst you are risking a health liability. If the resin was contaminated the liability would be very serious, indeed.

Q: What is the reason for using different injectors in a water softener control valve? We are a seasoned water treatment dealer but have never understood this.

Also, we have replaced a lot of old softeners that had heavy brass valves. We have been discarding these. Is this the economical thing to do or are these control valves worth anything?

– Missouri

A: These are both very good questions. Most dealers don”t understand brine injectors and, as a consequence, they install softeners that do not function properly.

Brine injectors are important components of water softeners because they are the primary way of withdrawing concentrated brine from the brine storage tank. Depending on their size, they dilute the concentrated brine to different concentrations, and they control the flow rate of the diluted brine before sending it to the softening resin. Hence the injector”s functions are to draw concentrated brine from the brine tank, dilute it and send it to the softening resin at the proper flow rate and within the specified time.

Why are these two functions important? To properly regenerate any resin (cation, cation, deionizer) the regenerant must be introduced at exactly the right concentration and at a specific flow rate.

For example, softeners require that the concentration of brine, at the resin, must be about 10 percent, by weight, (0.897 pounds of concentrated brine per gallon). Since the brine tank contains close to 100 percent concentrated brine, it requires dilution. The dilution is one of the functions of the injector. The proper concentration directly affects the capacity and hardness leakage of the softener. Also, softener design engineers take into account the volume of water above the resin because it further dilutes the brine.

Also important is the flow rate of the diluted brine as it passes through the resin. This should be 0.5 gpm per cubic foot and should be completed between 20 to 40 minutes. The injector controls this and as you can project, the volume of resin determines the size and configuration of the injector. The more resin being regenerated, the larger the required injector. The best injectors maintain close to the same brine draw rate and the same diluted discharge rate over a wide pressure range. Others perform well only in a very narrow pressure range.

As an equipment designer I have always taken the above parameters very seriously both in designing a series of different sized softeners and in designing industrial softeners.

To your question about brass control valves, I don”t know of any common ones that cannot be easily rebuilt by using reasonably priced internal parts. The brass castings, assuming no severe trauma, will last dozens of years.

David M. Bauman, CWS-VI, CI, CCO, is technical editor of Water Technology® and a water treatment consultant in Manitowoc, Wis. He received his B.A. from the University of Illinois in Industrial Design. He can be reached by email at: [email protected].

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