Arsenic is chemically defined as a semi-metal, i.e. an element that has intermediate characteristics between those typical of metals and non-metals.

It is naturally present in the soil in the form of mineral rock (Arsenopirite).

In territories rich in arsenic-containing rocks, natural erosion causes the accumulation of this element in aquifers.

Health risks

Arsenic is known to be extremely harmful to human health. In particular, it is able to attack and damage DNA strands and acts as an inhibitor for many enzymes that perform important biological functions.

It is also known to be harmful to the nervous and the gastrointestinal systems; in massive doses it is lethal.
Some arsenic compounds are known to be carcinogens.

Because of how dangerous this element is, European directives are very restrictive regarding the maximum permissible concentration of arsenic in water intended for human consumption.

The limit laid down in Directive 98/83/EC is 10 μg/l.

Eliminate arsenic from water

Several techniques have been developed to remove arsenic from water and are used successfully worldwide.

The most effective techniques are listed below.

  • Adsorption onto granular ferric hydroxide
  • Reverse osmosis
  • Selective ion exchange resins

How much arsenic is in my water?

To ascertain the concentration of arsenic in the water used, a specific chemical analysis must be carried out.

For residents of the province of Viterbo who use mains water, there is also the option of consulting the street directory provided by the local healthcare authority. The street directory allows you to determine from which aqueduct your mains are served and to check the arsenic concentration.

All relevant information can be found on the Viterbo Local Health Authority website:

Removal of arsenic by adsorption onto granular ferric hydroxide

Adsorption is a specific chemical-physical process in which the surface of a substance in the solid state (called the adsorbent) fixes molecules or ions coming from a gaseous or liquid phase with which it is in contact. In this specific case, the solid adsorbent is granular ferric hydroxide.

The process of eliminating arsenic with granular iron hydroxide  is the only means that guarantees the abatement of the arsenic in both of its oxidation states (As (III) and As (V)), thus it is able to work without upstream oxidation.

The arsenic is adsorbed by the filter material (granular Ferric Hydroxide), which is located in a specially created filter which is crossed by the water to be treated.

The filter material also maintains a good porosity for long periods of operation, given that the particle size is very homogeneous (between 0.2 and 2.0 mm) and has a high microporosity, and therefore a good ability to capture the arsenic.

Adsorption onto granular ferric hydroxide is currently the most widely used technology for arsenic removal worldwide as it is both safe and effective.

Gajarda is the exclusive distributor of the G-OX product, guaranteeing low costs and immediate delivery times.

Filter backwashing

The filter material must be backwashed periodically to  allow for the correct operation of the system.

During the filter backwashing process, the water flow within the filter is reversed and the flow rate is increased; in this way, the water vigorously shakes up the filter material, homogenising it and eliminating any preferential channels formed by the water during the filtration phase, as well as eliminating various impurities deposited on the filter bed.

Filter backwashing is managed by opening a valve that can be manual or automatic.

The manual option requires the operator to decide when to backwash the filter by manually operating  the valve.

The automatic control valve instead allows you to programme the frequencies of the backwashes that will be managed in a fully automated way.

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