Q: Hi Professor: I have a customer who has well water iron and needs to remove it for irrigation purposes. The raw water has 13 mg/L (ppm) of iron and a pH of 6.5. Water usage will be between 2,000-3,000 gallons per day. The main concern is the staining of the bordering cement and brick improvements, not to mention the eventual clogging of the sprinkler heads. Do you have any suggestions?

A: For iron at this concentration you need to oxidize it first. Iron from a well is usually in the ferrous (Fe²) form. It is referred to as being dissolved and it is clear (no color). In this form it will pass, unfiltered, through most filter media. When it is oxidized, by feeding chlorine, by ozonation, by feeding hydrogen peroxide or by using a filter media which oxidizes iron, it becomes ferric (Fe³) iron. Ferric iron is reddish and is a filterable particulate.

After you do one of the above, there should be a filter tank (unless you use an oxidizing filter) with media of proper granular size to filter the ferric-particulate iron. The filter will require periodic backwashing to flush the iron to the drain and leave the filter media clean and ready to remove more ferric iron.

You will need to determine the flow rate at which the feedwater will pass through the filter(s) for proper sizing. I'm assuming from your location that you have very low hardness but you need a more complete analysis before proceeding.

Q: I have high amounts of iron in my unsoftened water. I have a Birm filter, a softener and a Centaur carbon filter, in that order. The six-year-old resin bed keeps fouling. All the equipment is large for a house … 2.5 cubic feet each. When the resin fouls the iron taste in the water is high and it is very hard.

I just replaced the Birm this weekend. The resin fouled again. I treated it with resin cleaner, bleach and then regenerated it twice. It's working now but who knows for how long.

That treatment has been used multiple times in the last year or so. I think it may be time to change the resin, but it certainly has had a short life.

Do you have any suggestions? I have a resin treatment feeder as well. Do you recommend this? What type of resin should I buy? I have a fine basket strainer so I can use fine mesh resin. I did notice when I emptied my Birm filter that there was about half what there should have been and there was no gravel. I put 2.5 cubic feet in as well as gravel. It was then 3/4 full. Is it possible that it breaks down over time or was not enough put in when it was first set up? Thanks for your guidance.

A: A more complete water analysis plus other information on your system is required in order to provide you with a good response. However, I'll comment on a few things that stand out in your situation.

From what you wrote, I have no idea why you have a carbon filter. Barring other information I would not recommend it.

Fine mesh resin in the softener would also be a consideration because it may remove the iron more efficiently. Either fine mesh or standard mesh resin would be a good iron "polisher" (if they follow an iron filter) for iron that may not be removed by the filter.

Your softener may be too large for a house. No matter what size a house is, when someone takes a drink of water, rinses a glass, takes a shower, washes their hands, etc., the flow rate is always about the same. These flow rates would be in the range of one to five gpm (gallons per minute). Your treatment tanks are probably about 14 inches in diameter. It is possible that during times of low flow rates the water being treated by the softener is eroding a hole through the softening resin thereby not utilizing all the available capacity. Subsequent flows will follow the path of least resistance and use the same hole. This is called "channeling." The problem with it is that the resin adjacent to the channel is becoming exhausted while all the other resin remains untouched. The softener then prematurely passes hard water and iron.

If the iron in your untreated water is ferrous (clear when entering the house) and not too concentrated you may not need the Birm iron filter. Most groundwater iron is in this form. If you do need the iron filter the 14-inch diameter is alright because filtration rates should be lower, per square foot of surface area, than a softening rate. But, iron filters should always precede softeners to prevent the very problem you're having, iron fouling of the softening resin. Your filter is in the wrong place.

If you feel that your large house occasionally requires a higher flow rate to fill a pool, wash three cars at once or take three showers at once then there should be a treated water storage tank to draw from.

Resin cleaners are primarily intended to dissolve ferric (oxidized and colored) iron converting it into ferrous iron, which can easily be rinsed out. Routine regenerations with sodium chloride or potassium chloride cannot remove iron in the ferric form but can in the ferrous form. Earlier I wrote that most groundwater iron is clear and dissolved but when it stays in the resin too long it oxidizes to ferric iron and penetrates deeper into the resin beads.

The resin cleaners and weak acids, if allowed to soak into the resin, dissolve and loosen this ferric (reddish) iron. The extra regenerations that you performed are very useful in rinsing out the cleaner and the newly dissolved iron. A resin cleaner feeder is fine, but if working you should not need to do periodic cleaning plus the extra regenerations.

I don't know why you used chlorine (bleach) in your softener. Chlorine presents two problems. It has the opposite effect on iron that resin cleaners have. It oxidizes dissolved (ferrous) iron, thereby keeping it in the resin, and it is harmful to the resin because it breaks it down, thereby turning the resin to mush, causing resin loss (shortens its life, as you say). Don't use bleach or other concentrations of chlorine except in rare circumstances.

The loss of Birm and gravel is only unexplainable if the lower collector has failed, whereby the Birm should have ended up plugging your faucets and/or collecting in your water heater.

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: dp-bauman@sbcglobal.net.

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