|
PREMESSE GENERALI SULLA TECNOLOGIA |
L'ozono è la molecola triatomica dell'ossigeno. L'ozono è un organismo composto da tre atomi di ossigeno (O3) presente allo stato naturale nell'atmosfera. E' il più potente tra gli ossidanti ( 10 volte il doro) e permette di distruggere batteri, virus e funghi e altri agenti organici con grande efficacia.
|
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| I VANTAGGI DELL'OZONO |
I vantaggi fondamentali dell'ozono sono:
|
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
|
ESEMPI DI IMPIEGO DELL'OZONO
|
IMPIEGO DELL'OZONO - PROPRIETÀ' Le applicazioni dell'ozono si basano soprattutto sulle grandi capacità disinfettanti che questo gas dimostra di avere.
L'ozono, grazie al suo grande potere ossidativo, è in grado di rompere i grossi componenti macromolecolari che sono alla base dell'integrità vitale di cellule batteriche, funghi, protozoi e virus. Questa sua potente azione disinfettante ad ampio spettro d'azione si presta per i seguenti impieghi.
|
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
|
RAFFRONTO CLORO - OZONO
|
NB. |
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
|
Tempi per la distruzione di:
microrganismi batteri protozoi virus protozoi virus muffe fermenti |
Tempi indicativi per la distruzione di microrganismi con ozono
Tempi indicativi per la distruzione di BATTERI
Tempi indicativi per la distruzione di PROTOZOI
Tempi indicativi per la distruzione di VIRUS
Tempi indicativi per la distruzione di MUFFE
Tempi indicativi per la distruzione di FERMENTI
Tempi indicativi per la distruzione di ALCUNI AGENTI BIOLOGICI IMPIANTI CONDIZIONAMENTO
|
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Tabella esemplificativa |
|
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Relazione CNR - IRSA |
Physico-chemical treatments
The present situation Because of their higher costs with respect to biological treatments, physico-chemical water and wastewater treatments are essentially used to remove, degrade or recover non-biodegradable inorganic (e.g., metals) and organic (e.g., pesticides) pollutants. From the environmental standpoint, the main problems associated with these pollutants are their increasingly frequent occurrence in groundwater resources used for drinking purposes and the growing difficulties that economically significant industries (e.g., tanneries, textiles, paper-mills, olive oil-industry) have in achieving the COD limits fixed by existing and expected future regulations at reasonable costs. Of course, pollutants recovery and reuse represents the most desirable option. However, since, even when possible, such an option can be implemented only by means of rather expensive technologies such as ion exchange and membrane filtration, it is economically feasible only in the case of really valuable species that can be reused in industrial processes. In all other cases - the majority - the technologies employed are aimed solely at removing the contaminants. Metals (ions), which cannot be degraded, are normally removed by chemical precipitation, although this produces large quantities of toxic sludge that must be disposed of in the environment. As non-biodegradable (recalcitrant) organic pollutants can be either physico-chemically removed or chemically degraded, several different options are available for controlling their concentration in water and wastewater (i.e., stripping, adsorption, membrane filtration, chemical oxidation, etc). The choice of the most appropriate option has to be made case by case, even taking into account the fact that each of them is characterized by specific drawbacks respectively related to air contamination, disposal of exhausted carbon and/or membrane concentrates and formation of toxic oxidation by-products. It can be easily argued, then, that except for chemical-oxidation processes, using all the above technologies merely shifts pollution problems from one phase (the liquid) to another (solid, liquid or gaseous). Current trends and related technological and scientific implications According to the above considerations, the present need for more "environmentai~friendly" technologies is driving research in two main directions, i.e., in the case of metals, towards reducing the costs of removal and recovery technologies by seeking new and cheaper natural or synthetic ion-exchangers and membranes: in the case of organics, towards the development of new oxidation processes for transforming pollutants into C02 (Advanced Oxidation Processes = AOP) or into more biodegradable intermediates (integrated Physico-Chemical + Biological Processes). From the scientific standpoint, the selectivity of the above new materials has to be compared with that of those currently available and any resulting differences need to be explained on a scientific basis. From the technological point of view, instead, the possibility of recovering the metals removed from exhausted materials by means of innovative processes (e.g., combustion) is a topic of great interest. Referring to recalcitrant organic pollutants, one of the most interesting scientific issue is the analytical identification of oxidation by-products in order to assess whether their toxicity is greater or less than that of their parent compounds. In addition, much remains to be done in order to achieve a full understanding of the structural modifications caused by the oxidation processes leading to recalcitrant pollutant biodegradability enhancement. From the technoiogical standpoint, one of the latest trends is that of trying to set up integrated processes by which nonbiodegradable effluents are partially oxidized in order to improve their biodegradability and then biologically treated in order to avoid the costs of full chemical oxidation treatment. IRSA-CNR Research The main IRSA-CNIR achievements in the field of metals removal and recovery include the set up of three processes named MEXICO (Metal Extraction Xanthate Inertization and Chemical Oxidation), IERECHROM (ion Exchange Recovery of CHROMium) and IERAL (ion Exchange Recovery of Aluminum). In particular, the MEXICO process can be used to remove metals such as Hg, Ag, Cu, Cd and Ni first removed by selective precipitation of insoluble metal-xanthate complexes which are then recovered for recycling by oxidative treatment of the precipitates. In the IERECHROM process), Cr(111) is selectively removed from segregated tannery industry streams by means of carboxylic ion-exchangers. The concentrated Cr(111) solution resulting from the regeneration of exhausted exchangers carried out using H202 at basic pH is recycled in tanning baths. By means of the IERAL process, after acid (pH 3.5) elution of sludge containing aluminium and iron ions (e.g., sludge resulting from the coagulation step carried out at potabilization plants) the metals are selectively removed and recovered by selective ion-exchange. The highly pure metal solutions obtained after ion-exchange resin regeneration can easily be recycled back to the potabilization plants. In the field of non-biodegradable pollutants, the possibility to enhance the biodegradability of industrial wastewater by means of a partial oxidation has been demonstrated by treating with ozone real textile wastewater. Some interesting recent results concerning micro-pollutants occurring in groundwater resources indicate that when methyi-thio-triazines (i.e., a class of herbicides widely used all over Europe) are present during water chlorination (i.e., disinfection) they are rapidly removed and sequentially transformed into by-products whose toxicity decreases progressively. Herbicide (prometryne) degradation and associated by-products formation during groundwater disinfection by chlorine COD and BCOD trends during real textile wastewater ozonation Toxicity reduction occurring during prometryne contaminated groundwater disinfection by chlorine
|
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
