This expert water quality guide considers the process of iron and manganese removal from water supplies and why it is important. The guide looks at the problems higher concentrations of both minerals can cause and the importance of water testing. It concludes with a review of the most popular options for the treatment of water containing higher levels of iron and manganese.
Removing iron and manganese from water
Iron, manganese and other elements are naturally occurring in the earth and are common minerals and sediments.
In surface water, iron and manganese concentrations are generally fairly low.
In groundwater however, concentrations of both can be significantly higher, as the water spends longer underground in contact with the rocks containing these minerals.
What problems do manganese and iron cause?
Although manganese and iron are common and naturally occurring, they can cause various problems when found in a drinking water supply.
High levels of manganese and iron can discolour the water or laundry, and cause a metallic flavour in the water when drunk.
Very high levels of dissolved iron or manganese can have a detrimental impact on the disinfecting properties of chlorine from working efficiently.
In water where manganese and iron build up on the internal surfaces of a water system including pipes, storage tanks and other equipment, this can result in a decrease in water pressure.
Lower water pressures can also increase demands for power, and a hike in your organisation’s energy bills.
The benefits of water testing
The first step in identifying any problem, or indeed if there is a problem with your water supply, is to test the water itself to establish whether iron and manganese are present, and in what concentrations.
There are different forms of manganese and iron in both surface water and groundwater.
The most common forms are Fe2+ and Mn2+ which are both soluble, and Fe3+ and Mn4+ which are insoluble.
Other forms of both minerals are sometimes found but this will depend on the water conditions, or the level of acidity/alkalinity and microbes present in the water.
All the different forms of iron and manganese have their own properties, so it’s essential to understand what is in the water supply in order to choose the most effective water treatment option.
For drinking water, there are minimum standards which dictate the maximum levels of both manganese and iron in the water and these are:
Water treatment for the removal of iron and manganese
The most common way of treating water with levels of manganese and iron at greater than 1mg per litre is either oxidation or aeration.
Filtration is also a possibility but water treatment methods using coagulation, filtration and sedimentation are better for higher concentrations of solids.
This is particularly the case when the metals are dissolved in the water.
Options for treating water contamination
There are a number of popular options for the treatment of water containing higher levels of iron and manganese and they are considered here.
Oxygen in the atmosphere will readily oxidise iron.
Manganese doesn’t oxidise so readily, but using aeration can provide enough dissolved oxygen in to the water to change both manganese and iron into solids.
Using air to oxidise manganese and iron is cost-effective as there is no need to buy additional chemicals.
However, there are disadvantages too.
Oxidation can be slow when the levels of manganese are high, and the process requires a large water tank.
If the water quality changes, this can also affect the rate of oxidation and in some cases, may stop the process working altogether.
Manganese greensand is, as its name suggests a green sand that is effective at removing manganese, iron and hydrogen sulphide from water.
Over time, the manganese greensand will lose effectiveness, but it can be regenerated by using a solution of potassium permanganate.
If the concentration of iron in the water is very high, a continuous dosing of the sand using the potassium permanganate is often a better option.
Another option for oxidising manganese and iron in the water is to add chlorine, which changes the dissolved minerals into ferric hydroxide and manganese dioxide.
These are then filtered out from the water.
Adding more chlorine will speed up the chemical reaction.
Ozone is a gas which is made in a special ozone generator which passes electricity over an oxygen gas stream.
When dissolved in water, ozone is a very effective disinfectant.
Ozone oxidises manganese and iron to form particles which are much easier to filter out of the water.
Back-washable filters are the most effective with these applications and sand is most often used as it’s a simple design and a long-lasting way of removing manganese and iron.
Birm filtration media
Birm is a filtration media, it’s granular and contains a catalyst which precipitates manganese, iron or both.
Iron and the dissolved oxygen react when they come into contact with the filter bed, which precipitates out the iron.
Choosing the best iron and manganese removal solution for your water supply
There’s no one solution to treating water which has high levels or iron or manganese.
However, some sort of water treatment method is essential to make sure that the water is safe to use and is of a high enough quality to maximise energy efficiency and increase the lifespan of your plant and machinery.
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