Q
I have a resin analysis which shows that my customer has uranium, arsenic and nitrate in their well water. I have no idea how to treat this. Do you have any suggestions?
– Nebraska
A
Yes. Below is my edited version of a Purolite article on this topic from its website under PuroNews™, Volume 4, Issue 6 from June 28, 2004.
In the May 2004 issue of Water Technology, pages 56-59, is an article by Francis Boodoo of Purolite Inc. titled, “Multi-contaminant control with ion-exchange.” This can be seen in its entirety in the magazine itself or by downloading it from https://www.watertechonline.com by searching the archives for “Multi-contaminant.”
According to Purolite in its “entire” article, there is more detail on how you can help your customers control the costs of treating their water by ion exchange when there is more than one problem contaminant to deal with.
In today’s water treatment industry we have to remove contaminants such as you describe: Arsenic, uranium, tannins, sulfate and nitrate. These are all anionic. Similarly, you and your fellow water treatment dealers have often had experience with removing multiple contaminants in one vessel by top-dressing a water softener with an anion resin to soften and to remove nitrates and tannins. However, where the water hardness exceeds 10 grains per gallon it is best to use two separate units, cation then anion. In this case the second unit containing the anion resin will remove/reduce nitrates and tannins.
Also, a vessel containing anion resin will remove/reduce arsenic, uranium and nitrate … as in your question. This is not unlike an ordinary water softener which will remove iron, radium and barium. The caution here is that you must know the level of each of the multiple contaminants to be removed. You then need to determine the resin type and quantity required and its capacity for each of those contaminants. The questions in the Francis Boodoo article that need to be answered are:
• What is the capacity of each type of resin for each contaminant?
• Which resin is most suitable given its relative capacities and affinity for both contaminants?
• Which contaminant will breakthrough first and must therefore be used as the controlling factor to determine capacity and regeneration frequency?
• What dosage of brine (pounds of salt per cubic foot of resin) is adequate to handle each of the contaminants?
The answers to those questions can be obtained from the technical data sheets that are provided for every resin. Another way to determine the resin needed and its capacity is to do time-consuming pilot or bench testing. Or, computer software programs can make projections of various resin capacities for various contaminants. These programs are operated by the resin manufacturer for customers only. In the Boodoo article there are two examples of an ion exchange simulator that predicts resin capacity for more than one contaminant.
According to Contaminant Removal News™, Div. of Indumark®, Vol. 1, No. 1, August, 2007, it was reported that the design team who established that reverse osmosis (RO) and ion exchange could both be finalist treatment options that could remove all three contaminants in a municipal treatment plant. This analysis was done by two independent engineering firms (who consulted with RO experts), the municipal engineers and Purolite. In the end, ion exchange was selected due to its low waste generation (1/4thof RO for treated water) and its lower overall operating and capital costs. The new ion exchange plant now treats half the raw water supply, while treated water is then blended back with the rest of the raw water to produce the total flow for distribution.
A spokesperson for the city commented that wasted water (regeneration water and RO reject) was critical to them and emerged early as a leading concern.
“RO would have generated about 20-25 percent waste, which would be a substantial loss when the system peaks out at 5 mgd (million gallons per day) during the summer. By comparison, ion exchange was to run at only 1.5-2 percent waste for the total flow. RO would operate at a much higher pressure, 200 lbs./sq.in. vs. 25 lbs./sq.in. for ion exchange. This resulted in a calculated two to three-fold difference in energy costs. But despite these disadvantages, we knew RO could eliminate all contaminants, including any we found later that emerged as a concern, while ion exchange was assumed to be only contaminant-specific, and dependent on the makeup of the resin used,” noted the spokesperson.
Type II styrene anion resin, top-dressed with a specially-graded, strong base, acrylic anion resin was chosen. The water was hard enough that cation resin was required to pretreat the anion resin. Blending of raw and treated water achieved the required contaminant compliance, while also passing requirements of the EPA Lead and Copper Rule. Blending of raw and treated water reduces hardness from 490 mg/L to 325 mg/L. The pH of the raw water is 7.03 and the blended water is 7.3. This project took somewhere in the range of three to five years from conception to going online, including a pilot study.
Professor’s note: In no way am I intending to suggest that ion exchange would always be the best choice for the contaminants dealt with here. There were multiple factors involved in the case history described above. Even if one of these were different, reverse osmosis might have been the chosen technology.
Q
Over the months I have enjoyed reading your column, especially the one with water and mastitis in a dairy herd.
In a 2012 issue you made a brief and honest comment regarding a relatively new technology. I am interested in this because my engineering company is a small consulting firm specializing in industrial wastewater treatment primarily from hazardous waste sources such as steel mills, plating plants, printed circuitry and similar operations.
We have developed a new product, which we believe can be adapted to the residential water treatment market. Your 2012 article referred to new products needing performance certification, which we assume would give us a proven product with more marketing creditability. How can we go about getting certification?
– Illinois
A
In the past I had experience with the first NSF and WQA standard, WS100, for water softeners. I wasn’t sure how much of it applies today so I checked with WQA and I think what I have written here is fairly accurate.
There are various “types” of standards, such as performance, materials safety, etc. You clearly want a performance certification. The greatest hurdle, if I understand you correctly, is that there may not be a written standard and testing protocol for your product. If there is an existing standard it would be accompanied by a testing protocol. Having these would greatly simplify your project.
Barring this process, typical circumstance would entail a group of manufacturers with similar performance claims for their product(s) you, and others making similar claims, would get together with one of the agencies listed below and write a standard together with its associated testing protocol. Agencies that currently share, review and support standards for water treatment products are the WQA (Water Quality Association), UL (Underwriter’s Laboratories), NSF (National Sanitation Foundation International), CSA (Canadian Standards Association), IAPMO (International Association of Plumbing and Mechanical Officials) and ANSI (American National Standards Institute). I believe only the WQA, NSF and IAPMO actually perform the product testing.
Although you can begin by contacting any of the above, I recommend that you begin with WQA. They can tell you if a standard already exists and which standard(s) may be in progress. WQA is the only one of the above that exclusively exists to regulate and support the water treatment industry.
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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