Poor water quality problems sometimes present themselves as a mystery to be solved or as a risk needing to be taken for the betterment of what’s at stake. For this water treatment problem, consider the phrase made famous by the classic television program (and later, the group of movies) “Mission Impossible.”
“Your mission, should you choose to accept it, is to treat water with these parameters: …”
• Iron: 18.5 milligrams per liter (mg/L)
• Manganese: 1.1 mg/L
• Hardness: 65.8 mg/L
• pH: 6.2
• Total dissolved solids (TDS): 174 mg/L
• Hydrogen sulfide: Probable.
The response given (just before that fuse ignites): Ion exchange will gladly accept this mission.
Setting the scene
The bedrock in New England is loaded with iron deposits, and the acidic rain consumes it as it percolates through the soil. In this mission, we might drill a 6-inch hole 500 feet into the ground to tap into this “wonderful” supply. We could drill again, but the chances of improving the water quality with another well on the same 2-acre lot are slim to none.
With the prospect of a new home at this location, the new homeowners have no choice but to look at treatment.
Aeration had been attempted in the past on water of similar quality. It worked for a while, until the system had been operating for a year or two. The pipes started clogging from the precipitated iron, and the media didn’t last as long as when it was first installed.
In such a situation, the air draw on the pump cycle dropped from 50 percent to 10 percent, and the pressure switch got clogged with iron and caused the pump to short-cycle. Many items caused the system to fail — then iron would bleed through.
We had customers screaming at huge bills to rebuild the entire system, even as we explained: It’s your water quality. The system they had been using sure sounded good until we handed them the annual maintenance bill.
Starting our mission and learning from our mistakes, we turn to a fine-mesh gel cation resin as our workhorse. The smaller mesh resin has more surface area for high iron levels, and, due to its smaller size, can filter some of the insoluble precipitate formed from ferric iron (Fe+3).
We will use a large softening system that will alternate between two cylindrical tanks. This dual-alternating system ensures a “no hard water” bypass; with 18.5 parts per million (ppm) of iron, this is critical. If someone flushes a toilet during the regeneration cycle, no harm is caused.
On a single-tank system, an iron-staining call from the customer would be sure to follow. Most consumers don’t understand that, with such a flush or other heavy usage, they could have just introduced a huge amount of iron into their plumbing system.
Sizing of the dual alternating system is based on gallons throughput and not on days. This ensures the system will not run out of capacity before its next regeneration.
A meter option based on flow volume also saves on salt if there is varying water usage or the homeowner is away often.
Iron: the nemesis
Although fine mesh can handle some ferric iron, we must try to reduce iron as much as possible. We also are dealing with water from an artesian well and sediment is very probable. We will install a backwashing depth filter before the softener.
One could look at the pH and recommend a backwashing neutralizer first, trying to streamline the treatment train and reduce costs. Unfortunately, this is not a good idea.
When the pH of the water is raised with high iron, it causes some of the dissolved ferrous iron (Fe+2) to convert to ferric (Fe+3) iron and the latter’s resulting insoluble oxidized precipitate. As a result, depending on the pH and the severity of the iron, the softener will become iron-fouled.
Part of our mission also will be to choose a backwashing filter that does not oxidize, or affect pH. In the treatment train, the pH will be addressed after the water softener with a calcite neutralizer equipped with a backwashing control valve. Having softened the water prior to this element, we can expect to add approximately 4 to 5 grains of hardness to the water and easily balance the pH.
Add hydrogen sulfide to hit list
With high iron, hydrogen sulfide usually lingers in the background, causing odor issues. There is nothing worse than telling someone they just spent thousands of dollars on a water treatment system that doesn’t address odor.
If there is high iron, then hydrogen sulfide is usually present. Add it to the hit list, and treat it.
We will install a catalytic carbon filter to alleviate the hydrogen sulfide gas that may accompany this source water. Either a cartridge-based or a whole tank system may be used; whichever it depends on your customer’s budget. We would recommend the tank system for the homeowner’s convenience.
Key Points to Consider Concerning Poor Water Quality
• Ensure the systems regenerate frequently. The depth filter should regenerate every three days depending on home size, water usage and sediment encountered from the well. Having the neutralizer and carbon regenerate once a week is adequate — just enough to keep the bed fluffed and prevent channeling.
• Always use maximum salting on your water softener when removing iron. Ensure at least a 90-minute brine draw cycle. This helps with proper rinsing and good contact time for the ion exchange to occur.
• A “rust remover” salt is highly recommended, and a resin cleaner drip system should be installed.
• Recommend a concrete dry well dedicated to system waste discharge, with a service lid for future cleanouts if necessary. Never put this much iron and water into an on-site septic system.
• To treat this much iron, the water softener will add a significant amount of sodium to the water.
Homeowners concerned about sodium intake may want to consider a point-of-use reverse osmosis system for their drinking water.
A reliable solution
Water quality in New England has given us the opportunity to experience some very high levels of iron. After attempts with numerous systems, we have found the dual alternating, fine-mesh water softening system a suitable replacement for aeration, chlorination, and ozone.
Such a system is not a cheap alternative, but it often replaces the cheaper alternatives. It's low maintenance, reliability, and long life are an easy sell.
This mission is now complete.
Originally published by Carl LaChance in WaterTechOnline.com