By Marshall Craig and Justin Ramsey
The next time you are installing a residential water softener at a customer’s house, stop and take a look out the window. You might see unsightly red-to-brown rust-type iron stains on walls, sidewalks and plantings.
If you say to yourself, ”Too bad about those iron stains,” and walk away, you just missed a significant and consistent cash flow opportunity. As a water treatment professional, you do have the capacity to take care of water issues inside and outside the home, including iron stains.
When groundwater is tapped for irrigation landscaping, iron stains can be an undesirable side effect. As it happens, a number of forces are converging that increase the probability of iron stains appearing on walls and sidewalks across the globe.
First there is the growing interest in complex residential landscaping. This leads to increased use of home irrigation systems. But the increased use of irrigation has increased water demand, pushed city water prices up and stirred political debates on water usage.
In some communities across the US, the use of city water for irrigation is even verboten. Groundwater wells not only provide ‘free’ water for irrigation, but they are often mandated for irrigation usage.
Dealing with iron stains caused by irrigation takes two forms. You can simply clean off stains (facing the near-certainty that the stains will return when irrigation resumes) or you can install a system to prevent future staining.
Cleaning iron stains
In Miami, FL there are businesses whose main activity is simply spraying rust stain remover on curbing stained by irrigation. The process is not complicated. You apply an acid solution to the iron oxide stain.
The acid sequesters the iron and the stain disappears within minutes. It is best practice to flush off the treated surface with filtered water. This is because in some cases, depending on the acid used, a white powdered residue can appear against a dark background after treatment.
Another issue that can arise with cleaning off stains comes from the basic sequestering attribute of the acid. The acid cannot distinguish between an iron oxide colorant or a stain that is left by well water.
The operative rule in cleaning off stains: Try a small area first!
Preventing iron staining
The trick in preventing iron sprinkler stains is obviously to address the iron in the well water and deal with it before it comes out of the sprinkler head. Water treatment professionals are used to treating iron by filtration methods, getting the iron particle to accrete enough mass that it can be trapped and excluded from the water stream. This is a good and comprehensive method when addressing relatively low flow rates of water.
However, most residential and commercial irrigation systems involve, at the minimum, a one-horse power well pump, generating water flows upwards of 10 gallons per minute. In the Midwest, a one horsepower submersible is fairly standard for residential applications, generating typically 15-18 gpm in the sprinkler zones.
In Florida, one horsepower centrifugals sucking up water from twenty feet down can generate flow rates of 20-25 gallons per minute. Under these flow rate conditions, a filtration system would be cumbersome and costly.
The world of sequestering and chelating
There are chemical products that have an affinity for minerals, particularly iron and calcium in their unoxidized state. If these products can be introduced to ferrous (unoxidized) iron, they form a complex with the iron based upon charge in the case of sequestering and based upon physical positioning of the molecule in the case of chelating.
When the ferrous iron particle is bound up in this fashion, it will resist its natural inclination to add a few molecules of oxygen and enter the ferric state when exposed to oxygen. Sequestered or chelated iron will remain “bound up” under most all conditions, the exception being if it is hit by a strong oxidizing agent, with a pH of say, 10 or higher. Technically, chelated iron does not form a real compound with the chelating agent.
This is important to understand because the bulk of the iron found in a well is ferrous. If we can manage to introduce a sequestering and chelating agent to secure the ferrous iron before it comes out of the sprinkler head, we will eliminate or greatly reduce the stains caused by irrigation.
There may always remain the possibility of some staining because of ferric iron in the groundwater caused by iron bacteria, tannins or even ferric iron generated by rusting galvanized pipe. This is why options for cleaning are important to a total solution.
Feeding the well stream
Different means can be used to feed these agents into a stream of well water. They can be fed by either suction created by the Venturi effect or by injection.
From an operating cost point of view, no one approach to feeding the chelating solution into an irrigation line is more cost-effective per hour of operation than another.
In Florida and other areas where many above ground centrifugal pumps are used for irrigation, simple ‘siphoning systems’ can be used. Water treatment professionals are probably most familiar with the chemical injection process, where a peristaltic or diaphragm-type metering pump pulls a solution from a feeder tank and injects it into a line.
Installation of an injection pump and feeder tank is relatively straightforward. The desire is to feed chemical into the irrigation line when the irrigation system is operating via a pump start relay engaged by the system time clock that initiates power to the metering pump. In the case of larger multi-zones systems where only specific zones need to be treated, a second timer can be used that will address those zones of interest.
Most local codes require a back flow preventer on an irrigation system. The injection point for chemical should be downstream of the backflow preventer and before the first zone.
Agent and dosage selection
The next issue to address is the choice of a particular chelating agent and the proper dosage. There are a number of key factors that must be understood relative to hardness, pH, iron content in ppm, approximate maximum flow rate (largest zone) of the irrigation system, feed rate of metering pump and the volume of feed tank.
The pH is important because it can affect the choice of a chelating agent. Not all agents will perform well at the low pH levels found in some parts of the US. At the other end of the spectrum some agents, such as polyphosphates have a particular affinity for calcium so they are affected by the hardness of the well water. The pH and hardness, therefore can dictate which sequestering and chelating agent is used.
The remaining four factors determine the amount of chemical that is to be put in the feed tank. Using the iron in ppm, you can refer to charts that present dosage at various metering pump feed rates with feeder tank size and maximum flow rate of the irrigation system held constant.
The metering pump feed rate, combined with the size of the feed tank, determines how long it would take to empty a tank. For instance, a 30-gallon tank full of solution, tapped by a metering pump feeding at the rate of 0.25 gph would last for 120 hours of irrigation time.
If four gallons of chemical were needed at each refill (the rest of the tank being filled with water) and cost $15.00 (USD) per gallon, the operating cost of the rust prevention system would be $60.00 (USD) every 120 hours of watering. or $0.50 (USD) per hour of watering.
This $.50 per hour can be very attractive compared to municipal water cost in excess of $3 per thousand gallons. Note: an irrigation system flowing at 20 gpm uses 1200 gallons an hour!
Perhaps the most attractive part of installing rust stain prevention systems for a water treatment dealer is that it fits very well into a service-oriented business model. A rust stain prevention system represents a stream of income projecting into the future.
About the authors/company
Marshall Craig is the National Sales Director and founder of American Hydro Systems. He can be contacted by calling 800-285-9176 ext. 314 or by email at [email protected]. Justin Ramsey is Associate Brand Manager with Pro Products, LLC, located at 7201 Engle Road in Fort Wayne, IN 46804. The company markets Rid O’Rust irrigation chemicals and Rusty Stain Remover. He can be contacted by calling 800-285-9176 ext. 306, by fax at 260-490-9431 or by email at [email protected]. For additional information, visit the company’s website at www.proproducts.com.