Waterguide - Iron and manganese removal
Which removal methods are available?
Methods for removing iron and manganese compounds fall into four categories:
- Aerobic and micro-aerobic treatment
- Anoxic treatment
- Treatment using ozone
Aerobic and micro-aerobic treatment
The oxygen content is raised to over ≥ 4.0 mg/l, so that the iron and manganese can oxidise. The iron enters a trivalent state and the manganese enters a quadrivalent state. That is the aerobic treatment method.
In the micro-aerobic treatment method, the oxygen content is reduced, so that the bacteria can initiate oxidation.
This method uses the chemical nitrate for the oxidation process. However, it is a very time-consuming method and is not economical enough to be used on a large scale.
Treatment using ozone
Ozone is used to trigger the oxidation process when the concentration of iron is much higher. The iron enters a trivalent state and manganese enters a septivalent state. Next, activated carbon has to be used to reduce the manganese and enable it to precipitate.
You can also use iron removal filters, whereby the water passes through a material made of BIRM and hydro-anthracite which binds the iron and manganese. The filter can be regenerated through regular backwashing. This method is suitable for removing low quantities of iron and manganese.
In all of the methods described, the iron is removed first and then the manganese. This has proven to be the best order and is both fast and efficient.
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What types of water have to be treated?
Surface water usually has very low amounts of iron and manganese, which is why it does not have to be treated to remove these elements. Groundwater, on the other hand, has a very high concentration of iron and manganese, so it has to be treated before it can be supplied as drinking water.
The international specification for the concentration of iron and manganese in drinking water is 0.2 mg/l for iron and 0.05 mg/l for manganese.
The specifications in Germany are set by the German Drinking Water Ordinance (TrinkwV), but have to meet the thresholds set by the WHO.