HOMEBREW Digest #5684 Tue 25 May 2010

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  Sodium/Chloride ("A. J. deLange")

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---------------------------------------------------------------------- Date: Tue, 25 May 2010 09:41:21 -0400 From: "A. J. deLange" <ajdel at cox.net> Subject: Sodium/Chloride Dave asked whether there is an easy way to remove sodium and chloride ions from softened water. Easy? Relatively. Inexpensive? Depends on your definition but RO potentially qualifies. One can buy an 11 gallon per day RO system from Home Depot for $279 (and lots of other manufacturers, stores, websites... list lower priced units of around or even greater than that capacity). But why would you want to use a softener in the first place? It doesn't "remove" anything but rather only replaces polyvalent ions (calcium, magnesium, iron, strontium...) with equivalent amounts of (monovalent) sodium. Chloride is unaffected (except perhaps for minimal amounts from residual brine) as are bicarbonate, sulfate, nitrate.... If your goal is demineralized (or largely demineralized) water the task is of the same magnitude at the output of the softener as it would be if the softener were not used. Why not just feed an RO unit directly from the mains? It turns out there is a reason. If the water is hard (and we would'nt be having this discussion if it weren't) there will be a gradient of calcium ions concentration perpendicular to the membrane surface increasing in the direction of the membrane. If the hardness is temporary (carbonate) there will be a carbonate ion concentration gradient as well and, depending on pH, hardness, alkalinity, and recovery rate the concentrations of calcium and carbonate ions can exceed the solubility product close to the membrane surface with resultant precipitation and blockage. If the calcium has been removed by a softener then obviously this problem is solved (and it will be some other salt which will limit allowable recovery such as barium sulfate even though your water, we hope, contains only miniscule amounts of barium). So there is a reason to use a softener with an RO unit and, IMO, that's the only job for a softener in a brewery (except perhaps boiler feed). That said, if you go to HD, buy an RO unit and just hook it up to the mains you will probably be fine. I had two of these units in service (brewing only) for 4 years in one case and 5 years in the other on nominally hard water (about 110 ppm as CaCO3 - mostly temporary) and never changed out the membranes because I didn't have to. I'm on a well so my pH is low (that helps) and these GE units have low, fixed recovery (that also helps) of about 17%. On checking the GE manual for the recovery I found that they too recommend a softener if you hardness is greater than 10 gpg (about 179 ppm) and your pH > 7. That increases to about twice that level of allowable hardness at pH 6.7; three times that a pH 6.3 and so on. The manual also says the consequences of not using a softener above these levels is shortened membrane life. In the system which replaced those small units I feed softened water and feel quite comfortable operating it at a recovery of around 40% (which should make all you environmental types feel all warm and fuzzy inside). I'm not sure I understand why Martin would favor nanofiltration over RO for the likes of us. They will block the polyvalent ions (thus softening the water and decarbonating it, getting rid of sulfate and nitrate) but let the monovalents through so if deionized water is the goal additional processing would be required to get rid of the monovalents. I guess they are easier to clean but as I noted above I have never had to clean an RO unit. On an industrial scale I'm sure things are dramatically different and the processing methods chosen are determined by the particulars of the feed water chemistry, the requirements for the processed water and a whole lot of other considerations which include not only the capital costs (which he mentioned as being high) but operating costs, concentrate disposal and on and on. I know nanofiltration is becoming popular among water authorities these days but don't see it for homebrewers. But really, I know almost nothing about nano systems. A.J. Return to table of contents
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