By Ed Maas

In most instances, it is more practical and economical to remove iron from the water supply before we use it than to deal with the effects of clear- or red-water iron.

Iron is one of most troubling contaminants we deal with in traditional water treatment. It can be simple to deal with or very complex and can best be dealt with through ion exchange and oxidation/filtration processes.

Where does iron come from? First let’s review the fundamentals of our water supply. Most of our water used for domestic, commercial or industrial uses comes from either surface water or groundwater. Typical surface water supplies are void of iron.

The majority of our water supplies are groundwater, from wells that may be less than one hundred to thousands of feet deep. The water we use today is the same water that has been here since the beginning of time.

Water continuously travels through the hydrologic cycle. The hydrologic cycle is nature’s way of purifying water by evaporating surface water from the earth. As it reaches high levels in the atmosphere it condenses, forming clouds which eventually become so saturated that the moisture falls back to the earth in the form of rain, snow, hail or fog.

As this moisture falls on the surface of the earth, some of it soaks into the ground. Some of it runs off to streams, rivers, lakes and oceans.

Percolation and saturation
The water that soaks into the earth percolates through the upper layers of the geological strata and eventually recollects in porous ground strata known as zones of saturation. Wells are drilled into the earth until they reach these zones. More than five percent of the earth’s upper geological layers contain iron.

Water is known to be the universal solvent; it dissolves a little bit of everything it touches. As water percolates through the earth, it dissolves minerals that are in the soil; such as iron, manganese, calcium and magnesium, just to name a few.

Because the geology of the earth varies from one region to another, so does our groundwater. Supplies may have a little iron or extremely high amounts of iron. It may be naturally soft or so hard that it is virtually unusable for domestic purposes. It may be acidic or very alkaline.

Out of all of these variables, which are a direct result of the geology of any particular region, iron can be the most troublesome for water use. Iron is considered to be one of the most unstable minerals in our groundwater supply.

Clear or red
As water percolates through the ground strata, it dissolves the iron from the iron ore deposits as ferrous bicarbonate {Fe (HCO3)2}, sometimes referred to as clear-water iron. When iron is dissolved in water you cannot see it.

Iron normally wants to revert back to its natural state as iron ore. Dissolved iron very easily comes out of solution and precipitates to a solid particle of ferric hydroxide {Fe(OH)3}, often referred to as red-water iron. Simple changes to the water supply such as temperature, pressure or even a change of pH can promote the change from clearwater iron to red-water iron.

The addition of oxygen to a water supply may easily convert clear-water iron to red-water iron. Generally speaking, the higher the pH the quicker this reaction can take place. Iron will precipitate to a solid particle much faster at a pH of 8 than at a pH of 6. Thus, the pH of the water supply has a major impact on iron precipitation.

Iron effects
The effects of iron in a water supply are numerous. Iron will stain fixtures, water-using appliances or surfaces that the ironladen water contacts. These stains may vary from a light yellow to a red or light brown color.

Iron can give water a metallic taste that may be considered unpalatable. It may produce odors that are undesirable for domestic use, can foul water softeners and water-using appliances and plug water pipes or heat exchangers.

While none of these effects are hazardous to humans, water processing or to the environment, they cause consumers to spend hundreds and even thousands of dollars to clean and maintain appliances, homes and factories every year. In the process of cleaning and maintaining our homes or factories, we quite often use cleaning solutions that may be toxic or hazardous to people and the environment and all at a substantial expense.

In most instances, it is more practical and economical to remove iron from the water supply before we use it than to deal with the effects of clear- or red-water iron. Successful reduction of iron starts with proper identification of iron and other water characteristics that may affect the iron-reduction process. Proper testing and analysis of a water supply accomplishes this.

In iron filtration for domestic applications, we do not design or size by dosing limits. Systems are typically sized by influent contaminant levels along with required flow rates. Then we live by the golden rule of backwashing the iron out before it can coagulate to a particle too large to be lifted by the backwash flow rate.

At minimum, a water supply should be tested for: total hardness (TH); TDS; pH; alkalinity; manganese; tannin and iron and iron bacteria. Oftentimes, iron or iron-related symptoms are misdiagnosed and the wrong equipment may be applied. When this happens, typically the equipment will only work for a short period of time (if at all), which then may lead to it becoming fouled with iron.

Iron types
Most iron-reducing processes are designed to minimize either clear-water iron or red-water iron. There are other specific types of iron that can be identified and which may cause typical symptoms that are associated with iron.

Sequestered iron is normally found only in municipal water supplies. A sequestering agent has been added to the water supply while the iron is in the ferrous state (dissolved or clear water) with the intent to keep the iron in the clear-water state. Oftentimes a polyphosphate blend is added for sequestration of iron.

By encapsulating the iron ion with a sequestering agent, oxidation or conversion of the iron to the ferric (red-water) state is prevented. Unfortunately, many sequestering agents break down before water passes through our homes and factories, as it was intended. It should also be noted that sequestering agents prevent successful reduction of iron through most iron reducing systems.

Heme iron, as it is sometimes referred, is iron that has formed a compound with certain organics that may be in a water supply. This compound has similar characteristics to iron that’s been sequestered by polyphosphate compounds, so it too does not react to traditional iron-reducing technologies and typically passes through these systems. Often, additional technologies will be needed to remove organics from the water supply to achieve acceptable iron reduction. The addition of a tannin filter may be employed to remove organics along with residual iron.

Iron bacteria are probably the most often misdiagnosed iron related problem dealt with in water supply systems. Many times an iron-reduction system may be applied that will actually help these nuisance bacteria to grow and exacerbate the iron problem for the consumer.

Iron bacteria are live organisms that require oxygen as well as a food source (iron) to thrive and grow. While iron bacteria are not harmful to humans or animals regarding consumption, their presence and growth in a supply system can plug pumps, pipes and treatment equipment.

This will cause loss of water pressure as well as the typical symptoms of staining, foul taste and odor. Chlorination is the best known technology available to address iron bacteria. Iron bacteria should be controlled up-stream of iron reduction equipment.

Reduction processes
Iron reduction is simple once the type of iron in a water supply is properly identified and a good understanding of the water characteristics is determined. There are two basic technologies that are employed for iron reduction, as previously noted: ion exchange and oxidation/filtration.

Ferrous iron is a cation that in limited amounts can easily be removed with an ion exchange process such as a water softener. As a general guideline, many manufacturers will recommend a limit not to exceed two to five parts per million of clear-water iron (ferrous bicarbonate). Because variables in the water supply and the application have an impact on the success of the ion exchange process, it is best to consult with a professional water treatment dealer in your region to determine if the ion exchange process will work for your application.

Oxidation/filtration is typically employed where iron levels are high (greater than two to five parts per million) or where pH may be high (greater than eight), even when the iron level may be minimal. This process introduces oxygen to the water supply to convert clear-water iron (ferrous bicarbonate) to red-water iron (ferric hydroxide).

Once the iron is converted to a solid particle, simple filtration will remove it from the water supply. Today, an automatic backwashing filter is generally chosen to filter out precipitated iron particles.

It is important to make sure the filter is backwashed on a regular schedule to prevent the filter bed from becoming fouled. Many manufacturers recommend that intervals between backwash cycles never exceed three days and more frequently in many applications. Backwash intervals are based upon specific water supplies, applications and daily usage.

When iron reduction is required, consult with a local professional water treatment dealer as previously noted. It is the best way to obtain advice on what technology may fit your application.

About the author and company
Edward T. Maas is a Product Application Engineer for Hellenbrand, Inc., where he has been employed for 18 of the 37 years he has been in the water industry. Hellenbrand Inc. manufactures water treatment equipment and provides the industry with a wide array of water treatment products, including the patented chemical-free IRON CURTAIN™ filter system for residential and commercial applications.


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