The iron removal is a specific treatment for the removal of iron from the effluent to be treated, which otherwise could cause costly drawbacks, such as:
- Precipitation of insoluble hydroxides, with consequent obstruction of the pipeline, due to oxidation of ferrous and manganous ions, mainly present in well oxygen-poor water;
- Facilitation of the development of iron-bacteria that proliferate, using the iron precipitate as an energy source and forming a jelly with reddish color, which further aggravates the clogging of the pipes;
- Alteration of the organoleptic characteristics of water (taste and odor);
- Activating the bio-corrosion process of metals and degradation of cementations materials;
- In addition, the insoluble compounds determine the pollution of the ion exchange resin in the softener systems or membranes of RO systems, thereby drastically reducing their life cycle.
The iron removal can be performed in several ways, depending on the iron and organic matter concentrations in the water to be treated:
- Generally, for the water containing up to 5 ppm of iron and with a low concentration of organic matter, iron removal can be carried out by oxidation with air or chlorine and then followed by a quartz filtration. In alternative, a catalytic oxidation with a filtering support, composed of dioxide of manganese and quartz, sand can be used.
- PFor the water containing more than 5 ppm of iron, it is necessary to carry out the treatment in two stages. The first phase involves the precipitation of iron as iron hydroxide in alkaline condition, through the dosage of hydrated lime or caustic soda (alkalinisation clotting) and a subsequent dosage of a coagulant and a flocculants product. The second phase includes a filtration on quartz-zeolite filter for the elimination of the last traces of iron present in the water.
To improve the yield of iron removal and eliminate part of the organic matter present in the water to be treated, it is useful dose also a strong oxidizer, such as sodium hypochlorite. The excess of chlorine that remains in the treated water must be eliminated by filtration on active carbon, or by the dosage of bisulphite sodium.
Quartz- Zeolite filter
With this type of solution, we uses the oxidizing power of special catalyst supports (zeolite or manganese dioxide, MnO2), which have the capacity to transform the dissolved iron in the insoluble hydroxide iron and consequently easily removable. This material is mixed with the quartz sand, forming a single filter bed. Generally, it is used a multilayer bed formed by:
- Under-bed support in quartzite.
- Over-layer in charcoal of vegetable origin.
- Central Stadium in manganese dioxide with high quality and selected size of grains.
The action of the filtering beds also involves the manganese removal that is greatly reduced, up to 90 ÷ 95% of the inlet load.
The inlet water must be free of suspended substances, such as silt and clay, thus not to compromise the effectiveness of the oxidizing material.
This technology is used as an integral part of the treatment process in a Primary Water Plant.