Iron & Manganese Removal
People have struggled with iron (also called "rust") and manganese removal since the dawn of time. Adam complained to Eve that his new t-shirts were stained orangish-red (OK, I just made that up!). Removal of iron has been the topic of discussion between water treatment dealers for years ("my water softener removes iron better than any other softener, etc
."). The fact of the matter is that iron CAN be removed using an ion-exchange salt-regenerated water softener, but usually a water softener doesn't do it very long or very effectively. The best water softeners for removing iron are those that have twin softening tanks (one is always in service), which regenerate with soft water and fill the brine tank with soft water. If you have a water softener which removes ALL the iron, consider yourself as lucky as winning the lottery. Softeners work well to do just what they are supposed to do - soften the water by removing the calcium and magnesium, but iron (rust) is another animal and to remove it effectively, it usually has to be oxidized. Neither iron nor manganese in water present a health hazard. However, their presence in water may cause taste, staining, and accumulation problems. How to oxidize iron is the subject of this blog post.
Because iron and managanese are chemically similar, they cause similar problems. Iron will cause reddish-brown staining of laundry, porcelain, dishes, utensils, and even glassware. Manganese acts in a similar way but causes a brownish-black stain. Soaps and detergents do not remove these stains, and the use of chlorine bleach and alkaline builders (such as sodium carbonate) can actually intensify the stains.
Iron and manganese deposits will build up in pipelines, pressure tanks, water heaters, and water softeners. This reduces the available quantity and pressure of the water supply. Iron and manganese accumulations become an economic problem when water supply or softening equipment must be replaced. There are also associated increased energy costs, like pumping water through constricted pipes or heating water with heating rods coated with iron or manganese minerals. Most iron filtration systems operate on the principal of oxidizing the iron (oxidation) to convert it from a ferrous (dissolved or soluble) to a ferric or undissolved state. Once in the ferric state, iron can be filtered. Water filters are the most widely used equipment in removing iron. Its popularity comes from its versatility due to the various media products available and the process involved with each media. The most common reasons for filter failure are a lack of flow in backwash or a lack of frequency of regenerations. Low pH levels when using filters are another reason for unsatisfactory results.
For year, chlorine has been the oxidizer of choice. In addition to it's ability to oxidize iron, it also kills bacteria in the water. It does require a certain amount of contact time, so a drawback is that extra space is required for a retention tank (typically 24" x 72") or larger. Chlorine can be injected as a liquid before the pressure tank, or it can also be dropped down the well casing in the form of a pellet, using what is called a pellet chlorinator. This device is mounted on top of the well casing and is wired into the pump circuit, so that it runs when the well pump runs. You can calibrate it to drop pellets at whatever rate is needed to oxidize the iron at the source.
Following injection of liquid chlorine or chlorine pellets, the chlorine and oxidized iron/sulfur needs to be removed by a back-washing carbon filter. It is an excellent idea to "oversize" the filters as chlorine combines with organics in the water to form trihalomethanes (THM"s) which are known carcinogens. Make sure your carbon filter is big enough to properly remove them.
Water-Right, Inc. a company located in Appleton, Wisconsin has a very effcetive product called "The Sanitizer." The Sanitizer utilizes naturally silica zeolite, which is mined from the ground and is impervious to chlorine. During the brining cycle, two electrodes in the brine line generate large amounts of chlorine from the salt in the brine tank (NaCl is turned into Cl2). This is very effective at eradicating iron, manganese and even small amounts of sulfur.
Manganese greensand filters have generally been replaced with "Greensand Plus" media which is reported to be more effective at iron removal. Greensand is one of the oldest but proven oxidation technologies. Potassium permanganate, itself an oxidizer, is used to regenerate the greensand. In this application, potassium permanganate produces manganese dioxide on the surface of the mineral and — once the water comes in contact with it — any iron is immediately oxidized. The iron can be filtered and then cleaned away in the backwash cycle. Greensand is also effective with low levels of H2
S (hydrogen sulfide) and manganese. Greensand Plus is a granular mineral with a manganese dioxide coating having the same ability as regular greensand. It is much lighter and requires less of a backwash rate than standard greensand. The man drawback is the potassium permanganate which is a harsh oxidizer and produces a vivid purple color if any of it is introduced into the water. The tank that holds the potassium permanganate is subject to overflow which leaves horrid purple (black) stains in it's wake.
Injecting ozone into the water system is a very viable, albeit expensive, way to remove iron. Ozone is a powerful oxidizer and when used properly can be effective on large amounts of iron. Ozone is injected into water via a contact vessel as a pre-treatment to filtration. Ozone generators come in many designs and sizes and a full understanding of the process is necessary for success. Due to ozone’s expense it is usually applied on iron levels higher than normal filtration is known to handle effectively.
HYDROGEN PEROXIDE SYSTEMS
Hydrogen Peroxide (H2O2) is injected into the water ahead of a backwashing filter containing catalytic absorbative carbon. The iron and manganese and sulfur are oxidized and the precipitate is trapped and later backwashed out, by the backwashing filter. H2O2 is composed of the elements of water - hydrogen and oxigen and is excellent at removing iron, manganese and sulfur. The only drawback is theat you will have an annual hydrogen peroxide bill.
AIR INJECTION SYSTEMS
Oxygen in the air is an effective oxidizer and there are many ways to inject it into the water, including the use of "air pumps." A new development is the use of a valve that draws in a head of air and allows the iron to be fully oxidized before it goes through the media bed.
SPECIAL FILTERS (Birm, Filox, Pyrolox, Metal Ease, etc.)
Several companies make backwashing iron removal filters which remove iron utilizing special medias with manganese dioxide being the key ingredient. Birm has the ability to remove iron and manganese and has no effect on hydrogen sulfide. Like manganese dioxide, birm also uses dissolved oxygen as a catalyst and may require some type of pre-oxidation in cases where the dissolved oxygen content is too low to affect a maximum iron removal result. This technology is seldom the answer.
Manganese dioxide is a naturally mined ore with the ability to remove iron, manganese and hydrogen sulfide. The hydrogen sulfide capability exceeds that of either greensand or synthetic greensand and requires no chemicals to regenerate. It does, however, require adequate amounts of dissolved oxygen in the water as a catalyst and may require some type of pre-oxidation to achieve its maximum ability. Manganese dioxide sold under the names of Filox, Pyrolox, Metal-Ease and Birm. Filox seens to be the best of the bunch.
KDF-85 is a "Redox" media, which requires adequate dissolved oxygen to be effective, consists of two metals - 85 percent copper and 15 percent zinc. These two dissimilar metals create a small electrical field in the bed that will not allow bacterial growth in the media. This property earns redox the unique distinction of being effective on bacterial iron without the use of chlorine injection and being rated as bacteriostatic. Effective on removal of iron and hydrogen sulfide, able to reduce chlorine and heavy metals such as lead and mercury, redox is not effective with manganese. The biggest drawback for this media is its weight. Being almost twice as heavy as other minerals, it requires more than twice the backwash rate of other minerals.
More To Come