Q: I installed a combination of fine-mesh softening resin and tannin removal resin. After a few days the customer reports foaming at the drain during regeneration. I have never heard of this before. He says the foam looks solid, but it breaks up after a while. I think it is phosphate. What do you think this is?
A: I have heard of this and have replicated it under laboratory conditions. Remember, during regeneration not only does there exist at the drain all the removable anions and cations, but also the sodium and chloride from the regenerant.
All possible combinations of cation/anion salts will be present. Depending on the raw water analysis concentrations, the foam will not always appear. Another factor is the relative affinity of the resins for the various ions. This will determine each ion’s load and location on the resins.
Of the anions, bicarbonate is the first to be leaked during exhaustion. So, depending on when the regeneration takes place and how much bicarbonate is still present, one likely constituent of the foam will be sodium or calcium bicarbonate.
It is not particularly important to have this identified because there is not much that can be done about it. If it is a problem in a particular location, the alternative is to use two different columns.
Q: We are a satellite township that receives its water from a larger town, which is where, by prior agreement, all the treatment is done. The primary disinfection is the use of chloramines. These largely become depleted as the water reaches out to our smaller townships. The main treatment plant wants to add hypochlorite as a booster, but it will be done at the main plant. What is the impact or chemical reaction if a hypochlorite solution is used to boost the disinfection potential of a municipal system at the central treatment point?
— East Gwillimbury and Sharon, Ontario
A: This appears to be a very unusual approach to gain more disinfection. First of all, chloramines last longer in a distribution system than hypochlorite. So my first thought is why complicate the system with chlorine instead of just increasing the chloramination?
As part of my research I came across this U.S. EPA document, http://www.epa.gov/ogwdw/mdbp/pdf/alter/chapt_6.pdf. It indirectly addresses your question, but I cannot easily summarize due to its length.
Mine is not a thorough explanation due to the many factors that you will see in the 35-page EPA document. Much testing is recommended within the distribution system in order to know how much and what type of chloramine is present. pH, chlorine-to-ammonia ratio and other factors will affect which chloramine is formed. It also looks like, if the chloramines are mostly depleted, either the least desirable, trichloramine, is formed (you’d like monochloramine) or, if the chloramime is depleted, the result will be no different than common hypochlorite disinfection.
I am no expert on this subject, but it seems like the addition of chlorine will completely change its ratio to ammonia and will void all the reasons for chloraminating the water.
I’d welcome input from other readers who have municipal treatment experience.
Q: I’ve enjoyed your column in Water Technology magazine for several years. You always provide sound and practical advice to the questions and ultimately to the readers.
One topic, however, comes up from time-to-time and you’ve consistently answered the question in a similar manner, even though recent independent and credible third-party studies appear to indicate otherwise.
I’m talking about alternative technologies to ion exchange water softening for controlling hard water scale and, specifically, non-salt zero discharge systems. You’ve consistently stated that “no credible studies show these systems to deliver as promised. Nor have I read any credible explanations as to why the technology would work.”
The attached study and link were presented more than a year ago at the 15th Annual Water Reuse & Desalination Research Conference. It provides what many believe is credible third-party data that both explains alternative technology and provides evidence of it working. The link is http://www.watereuse.org/sites/default/files/u3/Peter%20Fox.pdf.
Do you feel differently after reading this paper? Will you change your responses to the subject of non-salt softeners?
Thanks in advance for your response.
A: The document for which you provided the link is actually the PowerPoint graphics intended to be accompanied by a verbal presentation. Its title is Evaluation of Alternatives to Domestic Ion Exchange Water Softeners. Consequently, it contained little text, making it difficult to understand much detail. However, I spoke with one of its authors who reviewed with me the results they thought were most significant.
The presentation was prepared by the University of Arizona. Its main purpose was to review technologies that have the potential to reduce scale formation, while minimizing wastewater and its salts.
The tables I reviewed, at the author’s suggestion, were those where no treatment was compared with four wholly different methods of hardness scale reduction. They are:
- Capacitive deionization (CDI), sometimes called EDI (electrodeionization), is a well known DI process, which should remove all minerals, and is not a softener alternative. This employs ionically-charged plates, which attract ions until the charge is reversed or removed when release takes place.
- Electrically induced precipitation (EIP). I could not find a photo or drawing of this so I don’t know anything about it except its test results.
- Template assisted crystallization (TAC). This is a polymeric bead that attracts calcium and magnesium ions at “neucleation” sites. The document only contained a drawing of a polymeric bead. The author, without further study, could not explain how it worked or state if it had a charge or how the hardness gets released, if at all.
- Electromagnetic water treatment (MAG). This is a wall-mounted power supply, which feeds two coils that are wound around a water pipe.
The water in the “results” tables was Tempe, Ariz. tap water and Tempe, Ariz. water at 140° F. I’m not sure if the water was 140° F or if that was the temperature of the heated water coil that was used to capture what I assume is the remaining scale after treatment. I also assume this simulated a water heater. Its scale was stripped and weighed.
|Grams of Ca as CaCO3 of scale formation captured.|
The PowerPoint conclusion states, “All alternative devices were effective at reducing scale.
- The most promising technology is the template assisted crystallization with scale reductions of over 90 percent.
- Further study is needed to look into the mechanisms at work for the magnetic treatment and a rapid testing protocol.”
My author/contact stated that it was not their intent to evaluate costs or to study how each method works.
In regard to my opinions, I’m still unclear, even about the results. As a group I would not refer to them as water softener alternatives because they apparently only reduce, not eliminate, scale formation. They also apparently do not prevent soap and detergents from combining with hardness. If I had heard the accompanying speech or was given some explanatory text I might feel differently because there appears to be some potential here. I look forward to seeing more studies on these technologies and, after looking at these test results, I think they should be referred to by their respective names and not as a group.