How to deal with manganese in your well water
Manganese is a mineral that occurs naturally and is usually found in sediment, rocks, and soils. This mineral is beneficial to the body and is found in most vegetables and grains. Though it is essential to nutrition, scientists state that manganese in water is very harmful to your health, even in concentrations as low as 0.5 ppm.
If you have deep water wells, the levels of manganese in your water should range between 2 to 3 ppm though you may have smaller amounts. Manganese levels as low as 0.5 ppm can lead to brown and black staining. The mineral often exists with iron, and these two together will cause chocolate-colored stains in your water appliances.
Generally, it isn’t easy to eliminate manganese from water because removing it depends on its oxidation state, total dissolved solids, and the presence of other minerals in the water under treatment. Moreover, manganese may appear with hydrogen sulfide or iron, making it even harder to treat.
Evidence of manganese in your water can often be found in your dishwasher, where the detergent will increase the pH of the water high enough to allow precipitation of the mineral; you can also observe toilet tanks where the minerals will appear as a floating film on the water surface. To make the film more prominent, you can shine a flashlight on the water’s surface.
What are the different forms of manganese?
In water, manganese takes two forms.
The first one is manganous manganese. This is the soluble state of manganese in the water. It dissolves in water the same way sugar does. Manganous manganese has to be precipitated first before being removed by a filter. You can also use a water softener to remove manganese in this form.
Once precipitation occurs, manganous manganese turns into an insoluble solid, which can darken the color of the water. In this form, it is called manganic manganese. The mineral in its precipitated state can be easily eliminated by a filter but cannot be removed by a water softener.
It is well to note that a water softener works by exchanging ions and does not filter out minerals. Thus, it can only exchange ions that have not gone through precipitation. On the other hand, Filters cannot eliminate iron or manganese if they are not in their precipitated state. You can use a softener as a filter for precipitated manganese, but they will be poor filters at best.
How do you remove manganese from water?
The water treatment used for manganese is the same as iron, though a few differences mainly involve pH. Filters will need a higher pH to remove manganese, unlike iron. Though it is easier to remove manganese using a filter if iron is also present. Manitoba well water is usually on the high side of the ph scale.
Can you remove manganese using a water softener?
A water softener is an ideal tool for removing manganese in the right conditions. The softener can accommodate large quantities of manganese provided they are in their unprecipitated state. The softener cannot eliminate precipitated manganese, and what’s more, it’s very harmful to the softener’s resin.
The following are conditions that affect the performance of a softener when treating manganese:
- TDS: A softener works more efficiently if the total dissolved solids (TDS) are low in the water. If TDS levels are high, then this means that other minerals are competing with manganese for resin space and may even displace manganese attached to the resin. The ideal condition is water with 500ppm or less TDS to remove manganese by a water softener.
- Dissolved oxygen: Low dissolved oxygen in water is more efficient when manganese is eliminated by ion exchange. This is because high levels of oxygen facilitate manganese precipitation. Manganese then turns to a solid form that a water softener cannot handle. This also applies to oxidizers other than oxygen, such as potassium permanganate, hydrogen peroxide, or ozone. Additionally, the water should not be chlorinated.
- pH: The experts recommendations differ, but generally speaking the pH should be lower than 8 for a softener to remove manganese as an ion efficiently. This is because precipitation of manganese occurs at high pH levels. The opposite is also true when using a filter.
Like iron, when removing manganese using a water softener, it is best to use a high dosage of salt and keep the service run short so that minerals do not build up on the resin. It is also vital to allow regeneration to occur frequently.
How can you remove manganese using a filter?
For manganese to be removed by a filter, precipitation must occur first. Therefore, it is crucial to have sufficient oxygen content and a high pH reading. These requirements vary according to different filter media, though primarily a pH greater than 8 will be needed for the filter to remove manganese effectively. For example, some very active media, Filox, can work at a lower pH, while standard ones, such as Birm, need a higher pH of around 8.5 to remove manganese effectively. With filters, you will need to use oxidizers such as ozone, potassium permanganate, or chlorine in pretreatment before filtration.
Eliminating manganese with a filter varies. Sometimes it is a simple process that uses a granular medium. At the same time, it’s more complicated and may require two to three processes that involve adding an oxidizer and amending the pH.
You can use a simple filter to remove manganic manganese. If your water has minimal amounts of the mineral, then a cartridge-style sediment filter is all that is needed. If the amount is high, you will need a backwashing filter containing multi-media, such as anthracite, sand, or garnet. The filter must also have a suitable sediment reduction medium.
You can use filter media as catalysts to convert soluble manganese to its solid form in cases where there is a relatively low concentration and the pH and oxygen content are relatively high. Media such as Katalox Light, Filox, and Birm will convert manganese to its physical form while filtering out the precipitated mineral. You will need to backwash the filter to restore the filter bed and rinse the trapped contaminants. These filters work best only when conditions are right. They work more efficiently when the iron in the water is more than manganese.
Pretreatment primarily refers to a free-standing oxidizer though it may also involve pH enhancement. Pretreatment is done through:
Aeration ensures the presence of dissolved oxygen needed for the removal of manganese. It might occur through either standard aeration or double aeration. This process also requires an extra step of enhancing the pH. Then any suitable filter medium will eliminate the manganese.
Chlorine is a powerful oxidation medium. The chlorination process is done through a pellet dropper which involves dropping calcium hypochlorite pellets into the well. It can also be done through a feed pump that injects liquid chlorine into the water line under pressure. The latter method will require 20 minutes or more residence time. You may need to use a pH increaser like soda ash injected along with the chlorine.
3. Potassium Permanganate
Potassium permanganate is a strong oxidizer often used with greensand filters and is drawn in when the filter is regenerating.
Besides the three mentioned oxidizers, you may decide to use ozone or hydrogen peroxide though they are not very popular.
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