Getting the Most Iron Out of Groundwater
My email lately has contained quite a bit of news and even questions about the latest water contaminant, PFAS. The real name for PFAS is a great big long string of words that I will not get into today. PFAS seems to be the latest contaminant of choice, and is the new darling of the media and our public health groups. In the future, I will write about PFAS and the issues arising from it, and I want you to be aware I am aware of this new contaminant. I have been writing about iron in water, and I will continue to do so.
In my last column, I talked about the two types of iron found in groundwater: ferric and ferrous. I also wrote about how to handle ferric iron, or rust. A simple cartridge filter will do a pretty good job of removing this visible iron. The downside of a cartridge filter, as I wrote last month, is that they must be changed, sometimes frequently, and they really have rather limited flow capacities.
In years gone by, my father and I sold a number of cartridge-type filters to customers who had rusty water. After several years, we began to investigate other types of filters that would work on ferric or visible iron. This search was driven, to some extent, by the fact that water softeners really don’t do well when rusty water is fed into them. Water softeners are just that — softeners — and, although some manufacturers claim that their softener also works as a filter, these units don’t do a very good job of filtration and quickly become plugged.
In our search for a better filter — and this was in the early 1960s — we found a rather simple unit that worked great on ferric or visible iron. These units were called silica sand filters. They consisted of a 21-gallon galvanized tank, which is one-half of the standard and very common 42-gallon hydro-pneumatic tank. These filter tanks had a top inlet, a bottom outlet, and a distributor screen or slotted pipe inside the tank at the outlet. The filter media consisted of a fine gravel that filled the bottom 3 or 4 inches of the tank, and then a special sand that came to within 4 inches or so of the top. The top of the filter had a removable cap on a rather large hole, one that someone could easily get his or her hand into. The cap was sealed with an O-ring.
We found these units did just an outstanding job when rusty water was fed into them. Actually, over time, a slimy layer of rust would form on top of the silica sand. The silica sand did a really good job of straining out the rust from rusty water. This type of filter had a couple of advantages. It could handle a pretty good flow rate — much higher than a cartridge filter. Plus, the customer didn’t have to buy new filters or use any chemicals. One downside was that it had to be backwashed from time to time. This was a manual job. But perhaps the biggest downside with this type of filter was that it did no good when it came to ferrous iron, or iron that is in solution in the water.
The backwash procedure, which I would guess the average homeowner had to do about once a month, consisted of reversing the flow and running the water from the bottom of the tank out the top. It helped a lot if the pressure on the tank was relieved and the top cover could be opened. The person doing the regenerating could then use a wooden stick or a gloved hand to loosen the top of the silica sand, which at times could be kind of crusty. After, the cover was put back on and flow maintained from bottom to top, flushing out the trapped rust. I had one of these in the first house I ever owned. The home had one of those fabulous buried tanks I have written about, and the filter worked like a charm. When I would begin regeneration after fluffing up the bed, I would put the regenerate water into a laundry tray since I had no floor drains in the basement of the house.
Gosh, the water being flushed out of the filter looked like concentrated orange juice or the famous Persian orange that Allis-Chalmers tractors were painted. About a double laundry tray volume was adequate to complete the regeneration, or backwash, as it was not desirable to get every last particle of iron out of the unit. The regeneration was completed by running some water from top to bottom in the normal flow pattern, readying the unit for another cycle. If you had one of those buried tanks — which produced a lot of ferric iron — and one of these filters, you were done with the iron. My wife has always said that this was a far more effective iron control than the first unit we had at our present house, which has a captive air tank. One thing was for sure: When you flushed one of these silica sand filters, the trapped iron was history and you were done with it.
As I recall, some manufacturers made a silica sand filter that was smaller in diameter than these “pot”-type filters we used. I think they even made some automatic units so homeowners didn’t have to regenerate by hand. These smaller-diameter units were not nearly as effective as the simple “pot”-type filters. I think the large-diameter of the media bed or sand really helped to strain the ferric iron, but I can’t prove that. Next time, I will write about some other types of iron filters, including some that used chemicals and others designed to work on ferrous iron — the kind you can’t see.
In southern Michigan, winter was late getting here and really started in very late January. Since then, we have had a storm of some kind of nature about every three days. We have had snow, rain and, the most disturbing of all, freezing rain. I’ve plowed and blown snow more times than I like to remember, and today, in late February, everything is either pure white or glare ice. The temperatures have been in wild swings, and this morning it was in the single digits Fahrenheit, with 50 degrees expected this coming weekend. We have had some soft winters lately, but not this year. ’Til next time. If you are shoveling snow, take it easy; if you got ice, be careful; and if you are in the South, be very thankful.
For more John Schmitt columns, visit www.nationaldriller.com/schmitt.