In Italy most of the drinking water comes from groundwater that, according to update surveys, are often polluted by organic chemicals such as chlorinated solvents and pesticides. These pollutants reach groundwater because of rainfalls, over irrigation and/or unauthorized disposals. The removal of such toxic and persistent pollutants at potabilization plants is achieved by specific treatments such as adsorption onto activated carbon or membrane filtration. However, these treatments are characterized by high cost and by the fact that the pollutants are transferred from the water phase to another phase (activated carbon or membrane retentate) which disposal is of environmental concern.
The alternative to the concept "phase transfer ' disposal" is the pollutants degradation into the water phase adopted by advanced oxidation treatments (AOTs). These innovative treatments are based on the high oxidizing power of a transient specie, the hydroxy radical (oOH), which, due to its high ox"red potential, is able to react with most toxic chemicals transforming them into organic by-products with much lower toxicity or into simple ions and/or molecules such as chloride, water, carbon dioxide, etc.
From the technical point of view the formation of hydroxy radicals can be obtained by a combination of : (I) two oxidants (O3/H2O2), (II) a catalyst and an oxidant (Fe+2/H2O2), (III) an oxidant and UV irradiation (UV/O3, UV/H2O2), (IV) UV irradiation and a catalyst (UV/TiO2), (V) UV irradiation, a catalyst and an oxidant (UV/Fe+2/H2O2), or finally (VI) an oxidant (H2O2) and ultrasonic irradiation. Each of the above technique constitutes a single AOT treatment and the choice of the most appropriate depends on several factors such as the kind of pollutant, its concentration, the degradation kinetics, the volume to be treated, costs, etc.
Another characteristic of the hydroxy radical is that it also acts as disinfectant. Therefore, during an AOT it is possible to achieve two goals at the same time: the removal/degradation of organic pollutants and water disinfection and this without the need to dispose of anything.
The Water Research Institute (IRSA) since several years is carrying out research on the effectiveness of AOTs for treating drinking water as well as industrial wastewater.
As for drinking water, the main results so far obtained by IRSA are the following:
o Degradation of pesticides widely used in Italy and in Europe (isoproturon, carbofuran) by conventional disinfectants/oxidants such as chlorine, chlorine dioxide, ozone and UV+ H2O2.
o Degradation of pharmaceutical intermediates (detected in North Italy groundwater) by UV+ H2O2.
o Degradation of chloro-phenols (2,4-dichlorophenol) by Fenton' reagent (H2O2 + Fe++).
o Degradation of industrial dyes (Uniblue-A) by ozone.
The following picture refers to an AOT reactor (1 m3/h) in operation at the Bari section of IRSA for the UV+H2O2 treatment of polluted drinking water.