| Title | Practical application of the Fenton reaction to the removal of chlorinated aromatic pollutants |
| Abstract | Background. Chlorophenols (CPs) constitute a group of organic pollutants that are introduced into the environment as a result of several man-made activities, such as uncontrolled use of pesticides and herbicides, and as byproducts in the paper pulp bleaching. Promising removal technologies of chlorinated aromatics consist in the application of advanced oxidation processes (AOPs) that can provide an almost total degradation of a variety of contaminants. Among these, wide application find Fenton systems based on generation of reactive species having a high oxidizing power, such as hydroxyl radical HO. Our objective was that of determining the overall degradation efficiency of the model compound 2,4-dichlorophenol (DCP) by thermal Fenton-type oxidation systems with a view toward defining in more details relevant process parameters, the effect of reaction temperature and of co-catalyst Cu2+.
Methods. Reaction conditions were similar to those generally adopted as optimal in many practical applications, i.e. pollutant/ Fe2+ (as FeSO4) ratio ca. 20, Fe2+/Cu2+ (co-catalyst) 2:1, pH adjusted and controlled at pH 3, and H2O2 in excess (up to four-fold over the stoichiometric amount required for complete mineralization).
Results and Discussion. The results demonstrate that it is advantageous to carry out the reaction at a temperature markedly higher (70°C) than ambient. The stepwise addition of H2O2 in aliquots yields an efficient transformation, while allowing a convenient control of the reaction exothermicity. Under these conditions, the essentially complete removal of the initial DCP is accomplished using just one equiv of H2O2 during 15 min; excess H2O2 (5 equivalents) yields extensive substrate mineralization. Also relevant, at 70°C dechlorination of the initial DCP (and of derived reaction intermediates) is remarkably extensive (35% residual TOX), already with the addition of 1 equiv of H2O2. At the end of the reaction, IC and IC-MS analyses of the solution reveal that only low-molecular weight carboxylic acid (acetic, formic, oxalic, malonic, tartaric, etc.) contribute to the residual TOC.
Conclusions. The whole of the results herein point to the advantage of performing the process at temperatures substantially higher than ambient (70ºC). Under the conditions adopted, almost complete degradation of the initial toxic compound can be achieved using hydrogen peroxide in fair excess (e.g., 3.5 equiv H2O2).
Recommendations and Outlook. In applying practical Fentontype degradation systems to heavily polluted wastes, either for the pre-treatment of waters with a high COD value prior to biodegradation or for complete mineralization of pollutants, the set up of appropriate reaction conditions appears to be a key factor. Also, it is desirable to keep the concentration of iron salts within the lower limits in order to minimize the production and disposal of iron oxide sludges.
DOI: http://dx.doi.org/10.1065/espr2003.06.155 |
| Source | Environmental science and pollution research international 10 (6), pp. 379–384 |
| Journal | Environmental science and pollution research international |
| Editor | Springer, Berlin, Germania |
| Year | 2003 |
| Type | Articolo in rivista |
| Authors | DETOMASO A., LOPEZ A., LOVECCHIO G., MASCOLO G., CURCI R. |
| Text | 170446 2003 Practical application of the Fenton reaction to the removal of chlorinated aromatic pollutants DETOMASO A., LOPEZ A., LOVECCHIO G., MASCOLO G., CURCI R. CNR IRSA, Universita di Bari Background. Chlorophenols CPs constitute a group of organic pollutants that are introduced into the environment as a result of several man made activities, such as uncontrolled use of pesticides and herbicides, and as byproducts in the paper pulp bleaching. Promising removal technologies of chlorinated aromatics consist in the application of advanced oxidation processes AOPs that can provide an almost total degradation of a variety of contaminants. Among these, wide application find Fenton systems based on generation of reactive species having a high oxidizing power, such as hydroxyl radical HO. Our objective was that of determining the overall degradation efficiency of the model compound 2,4 dichlorophenol DCP by thermal Fenton type oxidation systems with a view toward defining in more details relevant process parameters, the effect of reaction temperature and of co catalyst Cu2 . Methods. Reaction conditions were similar to those generally adopted as optimal in many practical applications, i.e. pollutant/ Fe2 as FeSO4 ratio ca. 20, Fe2 /Cu2 co catalyst 2 1, pH adjusted and controlled at pH 3, and H2O2 in excess up to four fold over the stoichiometric amount required for complete mineralization . Results and Discussion. The results demonstrate that it is advantageous to carry out the reaction at a temperature markedly higher 70°C than ambient. The stepwise addition of H2O2 in aliquots yields an efficient transformation, while allowing a convenient control of the reaction exothermicity. Under these conditions, the essentially complete removal of the initial DCP is accomplished using just one equiv of H2O2 during 15 min; excess H2O2 5 equivalents yields extensive substrate mineralization. Also relevant, at 70°C dechlorination of the initial DCP and of derived reaction intermediates is remarkably extensive 35% residual TOX , already with the addition of 1 equiv of H2O2. At the end of the reaction, IC and IC MS analyses of the solution reveal that only low molecular weight carboxylic acid acetic, formic, oxalic, malonic, tartaric, etc. contribute to the residual TOC. Conclusions. The whole of the results herein point to the advantage of performing the process at temperatures substantially higher than ambient 70ºC . Under the conditions adopted, almost complete degradation of the initial toxic compound can be achieved using hydrogen peroxide in fair excess e.g., 3.5 equiv H2O2 . Recommendations and Outlook. In applying practical Fentontype degradation systems to heavily polluted wastes, either for the pre treatment of waters with a high COD value prior to biodegradation or for complete mineralization of pollutants, the set up of appropriate reaction conditions appears to be a key factor. Also, it is desirable to keep the concentration of iron salts within the lower limits in order to minimize the production and disposal of iron oxide sludges. DOI http //dx.doi.org/10.1065/espr2003.06.155 10 Detomaso A., Lopez A., Lovecchio G., Mascolo G., Curci R. Environmental Science and Pollution Research, 2003, 10 6 , 379 384. 2003_ESPR.pdf Articolo in rivista Springer 0944 1344 Environmental science and pollution research international Environmental science and pollution research international Environ. sci. pollut. res. int. Environmental science and pollution research international. Environmental science and pollution research international Print Environmental science and pollution research Print ESPR Print DETOMASO ANTONIA antonio.lopez LOPEZ ANTONIO giuseppe.mascolo MASCOLO GIUSEPPE |
