Fentons Treatment

The technology behind Fenton s treatment dates back over a hundred years to 1894 when M.J.H. Fenton reported that ferrous ion promoted the oxidation of tartaric acid with aqueous hydrogen peroxide. Ferrous-catalysed hydrogen peroxide at acidic pH has since come to be known as Fenton s reagent and is widely used in both oxidative treatment of industrial effluents and in the manufacture of several types of polymers and polyelectrolytes. Subsequently, 

The use of Fenton s reagent as an oxidant has been applied to the removal of soil contamination.1617 It has been shown that pentachlorophenol and tri-fluoralin are extensively degraded18 while hexadecane and dieldrin are only partially transformed in a soil suspension at an acidic pH.19 

The application of Fenton s reagent as an oxidant for waste water treatment is attractive due to the fact that iron is a highly abundant and non-toxic element, 

The rate constant for the reaction of Fe(II) with hydrogen peroxide is high and Fe(II) is oxidized to Fe(III) in a few seconds in the presence of excess hydrogen peroxide. For this reason, it is believed that the majority of the waste destruction catalysed by Fenton s reagent is simply a Fe(III)-H202-catalysed destruction processes. 

The Fe(II)/Fe(III)-H202 system has its maximum catalytic activity at a pH of 2.8-3.0. Any increase or decrease in the pH sharply reduces the catalytic activity of the metal ion. At high pH, the ferric ion precipitates as ferric hydroxide, whilst at low pH, the complexation of Fe(III) with hydrogen peroxide is inhibited. To overcome this problem, Sun and co-workers have used Fe(III) chelates in place of Fe(II)/Fe(III).21 Sun has shown that a variety of herbicides and pesticides can be transformed and practically mineralized by Fe(II) chelates at neutral pH. 

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Figure 6.4 Features of beta zeolite after Fenton treatment, (a) Saito-Foley adsorption pore-size distribution from Ar-physisorption for (O) parent zeolite containing the template (no porosity) ( ) Fenton-detemplated and (V) commercial NH4-form BEA.

Friedman CL, AT Lemley, A Hay (2006) Degradation of chloroacetanilide herbicides by anodic Fenton treatment. J Agric Eood Chem 54 2640-2651. 

Wang Q, EM Scherer, AT Lemley (2004) Metribuzin degradation by membrane anodic Fenton treatment and its interaction with ferric iron. Environ Sci Technol 38 1221-1227. 

Rodriguez M, Sarria V, Esplugas S et al (2002) Photo-Fenton treatment of a biorecalcitrant wastewater generated in textile activities biodegradability of the photo-treated solution. J Photochem Photobiol A Chem 151 129-135... 

Idil AA, Betul HG, Jens-Ejbye S (2008) Advanced oxidation of acid and reactive dyes effect of Fenton treatment on aerobic, anoxic and anaerobic processes. Dyes Pigm 78 117-130... 

Ferrero, F. Oxidative degradation of dyes and surfactant in the Fenton and photo-Fenton treatment of... 

Treatment of olive mill wastewater has also been carried out with Fenton reagent [44]. This study also used Fenton treatment in conjunction... 

Although there are reports of improved biodegradation with Fenton pretreatment, there are also reports indicating limitations of Fenton pretreatment. Acid conditions often used for Fenton treatment are usually incompatible with microbial activity, and measures to overcome this incompatibility must be taken. For example, the use of iron chelators and higher pFi values is one approach that has been taken [61]. 

In the case of a biorecalcitrant textile effluent from a site in southern France, photo-Fenton pretreatment was not successful in improving biodegradability even when 70% of the effluent was mineralized by photo-Fenton treatment [90]. Aromatic intermediates were believed to be responsible for the recalcitrance of the pretreated effluent. 

Bench-scale tests revealed several important conclusions. First, the groundwater buffering capacity was found to be relatively high. This is a key issue because Fenton treatment is often ineffective at high pH due to iron precipitation. Bench tests also indicated that from some field-collected soil... 

Gernjak W, Krutzler T, Glaser A, et al. Photo-Fenton treatment of water containing natural phenolic pollutants. Chemosphere 2003 50 71-8. 

Emilio CA, Jardim WF, Litter MI, Mansilla HD. EDTA destruction using the solar fer-rioxalate advanced oxidation technology (AOT). Comparison with solar photo-Fenton treatment. J Photochem Photobiol A Chem 2002 151 121-8. 

Some papers (Brillas et al., 2004a Sires et al. 2006) have explored the effect of Cu2+ as co-catalyst in the electro-Fenton treatment of organics. The Cu2+/Cu+ system is also catalytic (Sharma and Millero 1988 Gallard et al. 1999) involving the reduction of Cu2+ to Cu+ with HO2 by reaction (19.21) and/or with organic radicals R by reaction (19.22)... 

Kinetic analysis of all concentration decays tit well with the equation related to a pseudo-first-order reaction (see the inset panel of Fig. 19.11). The last column of Table 19.2 lists the k -values thus determined for the comparative treatments of chlorophenoxy herbicides. Similar k values can be observed for all electro-Fenton and photoelectro-Fenton treatments with Pt. This discards direct photolysis of herbicides by UVA light and significant participation of reaction (19.24) to generate OH. 

Our group has also investigated the influence of a BDD anode, with much higher oxidation power than Pt, on the anodic oxidation with electrogenerated H202 and electro-Fenton treatments of chlorophenoxy herbicides (Brillas et al. 2004b). Solutions with 100 mg dm-3 TOC of 4-CPA, MCPA, 2,4-D, and 2,4,5-T of pH 3.0 were... 

Boye, B., Dieng, M. M. and Brillas, E. (2003c) Anodic oxidation, electro-Fenton and photoelectro-Fenton treatments of 2,4,5-trichlorophenoxyacetic acid. J. Electroanal. Chem. 557,135-146. 

Brillas, E., Boye, B. and Dieng, M. M. (2003d) General and UV-assisted cathodic Fenton treatments for the mineralization of herbicide MCPA. J. Electrochem. Soc. 150, E583-E589. 

Wang, Q. and Lemley, A. T. (2001) Kinetic model and optimization of 2,4-D degradation by anodic Fenton treatment. Environ. Sci. Technol. 35,4509—4514. 

The photoelectro-Fenton method [98] complements the photo-Fenton and electro-Fenton reactions. In the latter, a potential is applied between two electrodes immersed in a solution containing Fenton reagent and the target compound. The recent study of the herbicide 2,4,5-T, performed in an undivided cell with a Pt anode and an 02-diffusion cathode, showed that the photo-electrochemical process was more powerful than the electro-Fenton process, which can yield only about 60-65% of decontamination. The electro-Fenton method provides complete destruction of all reaction intermediates, except oxalic acid, which, as already mentioned, forms stable complexes with Fe3+ that remain in the solution. The fast photodecarboxylation of such Fe(III)-oxalate complexes by UV fight explains the highest oxidative ability of the photoelectro-Fenton treatment, which allows a fast and total mineralization of highly concentrated acidic aqueous solutions of 2,4,5-T at low current and temperature. A similar behavior was found for the herbicide 3,6-dichloro-2-methoxybenzoic acid [99]. 

In all its forms, the surface of carbon has oxygenated functional groups and these have been used as the starting point for the covalent bonding of functional groups to the surface. Moreover, in order to enhance the coverage by the functional groups, it has become common to preoxidize the surface by either an anodic treatment or the use of a chemical oxidant. While the properties of these modified surfaces are more suited to sensors, such modifications have been explored for effluent treatment applications. For example, an oxidative treatment of carbon felt was found to enhance the rate of destruction of 4-nitrophenol by an electro-Fenton approach [109] while chemical modification with hydrazine [110] and an anthraquinone polymer [111] has also been reported to increase the efficiency of electro-Fenton treatment. 

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