Degradation Of Non-Aqueous Phase Organic Pollutants By Modified Fenton's Reagent

The widespread use and improper of disposal of organic chemicals, especially non-aqueous phase pollutants such as Trichloroethylene (TCE) and Perchloroethylene (PCE), has led to significant contaminant of soils and groundwater throughout much of the world. As one of the advanced oxidation technologies, Fenton oxidation has been deeply researched in wastewater treatment. Recently, the technology attracts more and more attention in organic polluted groundwater remediation. However, there are still open questions concerning on mechanicms of non-aqueous phase organic degradation by Fenton reagent, such as the contribution of active species and the site that the reaction takes place. In this paper, we had focused our attention on the concerning questions, systemically studied the factors on degradated reactions by modified Fenton's reagent with iron(III)-ethylenediaminetetraacetic (Fe(III)-EDTA) chelator at neutral pH. The studies are such as follows:(1) There are different viewpoints of the degradation mechanism whether the organic phase can be directly degradated by modified Fenton's reagent, and which active species plays a major role in the reactions. In this study, PCE and TCE are present as dense non-aqueous phase liquids (DNAPLs) in solution system at neutral pH. The experiments were carried out with isopropyl alcohol as hydroxyl radical scavenger and trichloromethane as superoxide radical scavenger. These results showed that both hydroxyl radicals and superoxide radicals were generated in degradation reactions, and hydroxyl radical played a major role. There were no necessary relation between the concentration of the oxidant and the generation of hydroxyl radicals, and the directly degradation of non-aqueous phase PCE by modified Fenton's reagent.(2) Effect of operational parameters such as temperature, the concentration of chelator or oxidant, on PCE degradated reactions by Fenton's reagent were systemically studied. The results showed that the optimal reaction temperature was 40 centigrade, the optimal concentration of chelator was 5 mM, and the optimal concentration of H2O2 was 100 mM.(3) Surfactant was added to Fenton's reagent, and studied the DNAPL degradation by surfactant-Fenton system. Results were founded that the PCE DNAPL degradation by surfactant -Fenton was better than that only by Fenton reagent with the same conditions of reactions. There were inverse proportion between the concentration of surfactant and the effect of degradation.That is to say, the higher of the temperature when controlled in 20~60℃, the lower of the rate of degradation. And both hydroxyl radical and superoxide radical were possibly generated in reactions of PCE DNAPL degradated by surfactant -Fenton reagent.It's important of the paper to improve the efficiency of organic degradation by Fenton's reagent. And the paper can provide scientific gist for practical project of organic degradation by Fenton's achnology at home and abroad.