In situ oxidation remediation technologies: Kinetic of hydrogen peroxide decomposition on soil organic matter

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In situ oxidation remediation technologies: Kinetic of hydrogen peroxide decomposition on soil organic matter
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   Journal of Hazardous Materials 170 (2009) 627–632 Contents lists available at ScienceDirect  Journal of Hazardous Materials  journal homepage: www.elsevier.com/locate/jhazmat In situ oxidation remediation technologies: Kinetic of hydrogen peroxidedecomposition on soil organic matter Arturo Romero a , ∗ , Aurora Santos a , Fernando Vicente a , Sergio Rodriguez a , A. Lopez Lafuente b a Dpto Ingenieria Quimica, Facultad de Ciencias Químicas, Universidad Complutense Madrid. Ciudad Universitaria S/N. 28040 Madrid, Spain b Dpto Edafología, Facultad de Farmacia, Universidad Complutense Madrid. Plaza Ramón y Cajal S/N. 28040 Madrid, Spain a r t i c l e i n f o  Article history: Received 2 February 2009Received in revised form 15 April 2009Accepted 4 May 2009Available online 19 May 2009 Keywords: Hydrogen peroxideKineticOrganic matterSoil remediation a b s t r a c t Rates of hydrogen peroxide decomposition were investigated in soils slurries. The interactionsoil–hydrogen peroxide was studied using a slurry system at 20 ◦ C and pH 7. To determine the role of soil organic matter (SOM) in the decomposition of hydrogen peroxide, several experiments were carriedout with two soils with different SOM content (S1=15.1%, S2=10%). The influence of the oxidant dosage([H 2 O 2 ] o  from 10 to 30gL  − 1 and soil weight to liquid phase volume ratio=500gL  − 1 ) was investigatedusing the two calcareous loamy sand soil samples. The results showed a rate dependency on both SOMand hydrogen peroxide concentration being the H 2 O 2  decomposition rate over soil surface described bya second-order kinetic expression  r  H 2 O 2  = − dn H2O2 W  SOM dt   = kC  H 2 O 2 C  SOM .Thermogravimetric analysis (TGA) was used to evaluate the effect caused by the application of thisoxidantontheSOMcontent.ItwasfoundaslightlyincreaseofSOMcontentaftertreatmentwithhydrogenperoxide, probably due to the incorporation of oxygen from the oxidant (hydrogen peroxide).© 2009 Elsevier B.V. All rights reserved. 1. Introduction The contamination of soils remains a significant problem inrecentyearsinEurope.Insituchemicaloxidation(ISCO)showscur-rentalternativeforcontaminatedsoilsremediation.Whilemanyof the chemical oxidants have been used in wastewater treatment fordecades, only recently they have been used to treat contaminatedgroundwater by hydrocarbon and soil in-situ. One of the chemi-cal oxidation processes is the Fenton reaction, which uses H 2 O 2 as oxidant and ferrous ions as catalyst to generate OH • . It is aninteresting technology due to its high efficiency and low cost [1].This oxidant may be capable of converting the hydrocarbon masstocarbondioxideandwaterinsufficientcontacttimewithorganiccontaminants.However,hydrogenperoxidestabilityistheprimarylimitation of the use of catalyzed hydrogen peroxide propagationsfor ISCO [2,3]Theuseofhydrogenperoxidewasoncepopularbecauseitisrel-ativelyinexpensive,isnon-persistent,andisunlikelytobeahealthhazard if is used properly. However, oxidation treatment may alsohaveaneffectonthesoil.OxidativeprocessesinitiatedbyOH • couldalter the nature and speciation of the organic and inorganic con- ∗ Corresponding author. Tel.: +34 91 394 41 71; fax: +34 91 394 41 71. E-mail addresses:  aromeros@quim.ucm.es (A. Romero), aursan@quim.ucm.es(A. Santos), fervicen@quim.ucm.es (F. Vicente), goide26@hotmail.com (S. Rodriguez), lopezlafuente@farm.ucm.es (A.L. Lafuente). stituentswithinthesoil[4].Thechoiceofappropriatetechnologiesforsoilremediationrarelytakesintoaccounttheimpactonsoil[5].Several works have appeared which emphasized the efficiencyofFentonprocessesfortheremediationofcontaminatedsoilswithorganic compounds [6–11]. However, few works have studied the interaction hydrogen peroxide-soil by using the Fenton process[1,5,12], with achieving diverse findings probably due to the differ- ences among the soil type, soil organic matter (SOM) content andthe method for SOM quantification. For example, Villa et al. [12]found that 80% of the organic matter naturally present on the soilwas degraded while Sun and Yan [1] found an asymptotic valueof 30% for this degradation. Sirguey et al. [5] found differencesbetween SOM values before and after oxidation among 13% and90%, depending on the soil and the oxidant used (permanganateand Fenton reagent). Bissey et al. [3] studied SOM–hydrogen per-oxide dynamics with naturally-occurring soils minerals finding a30% SOM decrease after treatment with H 2 O 2  at acid pH (pH 3)while the SOM remained almost constant at neutral pH (pH 7).Ontheotherhand,itwasnoticedinliteraturethathydrogenper-oxideisdecomposedwhenitisincontactwiththesoil,evenwhenuncontaminated soil is used [3,13]. Scarce information is given in literature about kinetic aspects of H 2 O 2  decomposition rate. Firstorder for hydrogen peroxide has been assumed [13] as was alsofound for hydrogen peroxide decomposition using not soil but ironoxides as solid phase [14,15].The disappearing rate of the oxidant must be taking intoaccount to establish the required dosage of hydrogen peroxide 0304-3894/$ – see front matter © 2009 Elsevier B.V. All rights reserved.doi:10.1016/j.jhazmat.2009.05.041  628  A. Romero et al. / Journal of Hazardous Materials 170 (2009) 627–632 Nomenclature C  H 2 O 2  hydrogen peroxide concentration  g H 2 O 2  L  − 1  C  SOM  soil organic matter concentration (g SOM g soil − 1 ) k  kinetic constant (g soil Lg SOM − 2 min − 1 ) r  H 2 O 2  hydrogen peroxide decomposition rate  g H 2 O 2  g SOM − 1 min − 1  SOM soil organic matter (%)SQR weighted residual sum of squares   X  exper −  X  calculated  2 T   temperature ( ◦ C)TGA thermogravimetric analysis V  L   liquid phase volume (L) W  / V  L   soil weight to liquid phase volume ratio (g soil L  − 1 ) W  SOM  weight of soil organic matter (g SOM )   X  H 2 O 2   hydrogen peroxide conversion (%) Greek symbol   empiric stoichiometric coefficient  g SOM g soil − 1  g H 2 O 2  L  − 1  − 1 in the treatment of soils. Both SOM and organic pollutant cancompete for the hydrogen peroxide. Moreover, the SOM naturallycontained is usually much higher than the pollutant content andconsequently SOM could have a strong influence on the requiredhydrogen peroxide dosage for soil remediation. Therefore, the oxi-dantmustbeaddedinanamountenoughtoassurethecontaminantdegradation in the presence of the natural SOM.The amount of hydrogen peroxide needed to degrade a givenconcentration of contaminant in soil is often far greater than inaqueoussystems.IfthesoilcontainsappreciableSOM,therequiredH 2 O 2 /contaminantmolarratioscanbeintheorderof10 2 –10 3 [16].The reactivity of the hydrogen peroxide once H 2 O 2  and soil aremixed can be attributed to several reactions taking place simulta-neously. Some of the most relevant reactions and rate constant at20–25 ◦ C in the literature are below [17,18]: H 2 O 2 →  2HO • k 1 =  8 × 10 − 9 (1)H 2 O 2 + O 2 →  2HO 2 • k 2 =  1 . 3 × 10 − 19 (2)H 2 O 2 + HO • →  H 2 O  +  HO 2 • k 3 =  2 . 7 × 10 − 7 (3)HO • +  O 2 −• →  HO 2 − + O 2  k 4 =  9 . 7 × 10 − 7 (4)2HO 2 • →  H 2 O 2 + O 2  k 5 =  3 . 1 × 10 6 (5)2H 2 O 2 →  2H 2 O  +  O 2  k 6 =  1 . 3 × 10 36 (6)H 2 O  +  O 2 →  HO 2 • +  HO • k 7 =  5 . 4 × 10 − 41 (7)SOM  +  HO • →  products  k 8 =  10 7 –10 10 (8)CaCO 3(s) + H + ↔  Ca 2 + + HCO 3 − K  =  269 (9)HCO 3 − + HO • →  • CO 3 − + H 2 O  k 10 =  8 . 5 × 10 6 (10)CO 3 − + HO • →  • CO 3 − + OH − k 11 =  3 . 9 × 10 8 (11)HO • +  CO 3 − →  products  k 12 =  3 . 0 × 10 9 (12) • O 2 − + • CO 3 − →  CO 3 − + O 2  k 13 =  6 . 5 × 10 8 (13)H 2 O 2 + • CO 3 − →  HCO 3 − + • O 2 − + H + k 14 =  8 . 0 × 10 5 (14)HO 2 − + • CO 3 − →  HCO 3 − + • O 2 − k 15 =  3 . 0 × 10 7 (15)Although hydroxyl radicals, hydroperoxyl radicals, hydrogenperoxide and oxygen are all oxidants, hydroxyl radicals have the  Table 1 Properties of the soils samples.Soil Texture pH in water SOM (g SOM  g soil − 1 ) 100 Equiv. CaCO 3  (%)S1 Loamy sand 7.4 15.1 10.7S2 7.8 10 7.3 strongest oxidation capability, and are considered responsible foroxidizing organic compounds [19].The objective of the present paper is to research the kineticsand mechanism of H 2 O 2  decomposition on soils at natural neutralpH.Theoxidantagent(hydrogenperoxide)concentrationandSOMcontenthavebeenexamined.Thesoilswerecalcareousthroughouttheir thickness. Such little studied soils are abundant throughoutthe Mediterranean Basin and in Spain. 2. Materials and methods  2.1. Reagents Hydrogen peroxide 30% (w/w) from Riedel de Haën was usedinthedegradationexperiments.Titanium(IV)oxysulphatesolutionfrom Riedel de Haën was used in the determination of hydrogenperoxide. All of the suspensions and solutions were prepared withMilli-Q water (>18M  cm) purified with a deionizing system.  2.2. Soil samples The soils selected for this study (S1 and S2) were categorized asloamy sand at neutral pH. The main difference between the twosoil samples was the SOM content. The properties of S1 and S2are shown in Table 1. The soils were classified as calcaric Fluvi-sols (FLca). This is a type of soil that develops the basins of themainriversthattraverselimestonematerial,whichisthedominantmaterial in the eastern half of the Iberian Peninsula [20].The pH was measured in 1:2.5 soil/water suspensions [21]. TheCaCO 3  equivalent was determined by calcimeter Bernard method.TheSOMcontentinthesoilswasdeterminedbythermogravimetricanalysis (TGA), as described in Section 2.4.The SOM present in the soils S1 and S2 has also been burnedby incineration of a known weight of sample placed in a ceramiccrucible in an electric muffle for 2h at 550 ◦ C obtaining the corre-sponding SOM content by mass difference.  2.3. Experimental conditions of hydrogen peroxide decomposition Kineticforhydrogenperoxidedegradationwasstudiedforeachsoil through batch experiments, performed in vials, kept in con-tinuous agitation (50rpm) on a shaking water bath UNITRONIC,supplied by SELECTA The temperature was controlled, and contin-uously monitored during the experiments and remained always at  Table 2 Operating conditions of H 2 O 2  decomposition for runs carried out in batch tests. T  =20 ◦ C;  W  / V  L   =500gL  − 1 ;  u =50rpm.RUN Soil [H 2 O 2 ] o (gL  − 1 )Initial H 2 O 2  dosage  mg H 2 O 2  g soil − 1  Initial H 2 O 2  dosage  mg H 2 O 2  g SOM − 1  1 S1 10 20 1322 S1 20 40 2653 S1 30 60 3974 S2 10 20 2005 S2 20 40 4006 S2 30 60 6007 S1 20 40 SOM loss byignition8 S2 20 40   A. Romero et al. / Journal of Hazardous Materials 170 (2009) 627–632  629 Fig. 1.  Experimental (symbols) and predicted (lines)   X  H 2 O 2  vs. time values obtained in the decomposition of hydrogen peroxide by soil samples S1 and S2. 20 ◦ C.Theuncontaminatedsoilweighttoliquidphasevolumeratio( W  / V  L  )was500gL  − 1 .Theexperimentswerecarriedoutatdifferentinitial concentrations of hydrogen peroxide (10, 20 and 30gL  − 1 ).The soil pH was not adjusted. In order to avoid possible explosionsduetogasaccumulationinthevials,thecapswerenotsealedduringreaction time to permit evacuation of the generated gas [22]. Thesampleswerecollectedatdifferentreactiontimesandimmediatelycentrifugedfor5mininaCENTROLITSELECTAcentrifuge.Aftercen-trifugation,thesupernatantwasanalyzedforhydrogenperoxide,asdescribed below. Repeating the same batch experiment by sam-pling at different reaction times (0–1–5–10–20–30–40–60min)allowedtoobtainthekineticsofhydrogenperoxidedecomposition.These experiments were performed by triplicate.TheexperimentsconductedtoseparateSOMeffectinthehydro-genperoxidestabilityhavebeenperformedinthesameoperationalconditions with the two soil samples in which the removal of SOMfraction content by incineration has been achieved (runs 7–8 inTable 2). Fig. 2.  Conversion of H 2 O 2  on the soils S1 (a) and S2 (b) with and without SOM. [H 2 O 2 ] o 20gL  − 1 .  630  A. Romero et al. / Journal of Hazardous Materials 170 (2009) 627–632  2.4. Analytical methods Hydrogen peroxide concentration in the supernatant was mea-sured using a UV-1603 spectrophotometer, supplied by Shimadzu,after colour development with titanium sulphate technique [23].Thermogravimetricmeasurementswerecarriedoutinamoduleof simultaneous thermal analysis TGA/STDA 851 (Mettler Instru-ments). The SOM was determined by the mass loss in the intervalfrom150to550 ◦ Cinthethermogravimetriccurve.Thesamplewasheated in an alumina crucible. During thermogravimetric analysis,about13mgofthesampleswerefirstheatedinthethermo-balancein a flow of atmosphere air (20mLmin − 1 ) at a rate of 20 ◦ Cmin − 1 up to 550 ◦ C. Sequently, the samples were isothermally heated at550 ◦ C for 2h. 3. Results and discussion  3.1. Hydrogen peroxide decomposition Hydrogenperoxidedecomposition,withoutpHadjustment,wasmeasuredinordertocharacterizethereactivityoftheselectedsoils.Hydrogen peroxide concentrations were monitored with time attwo values of SOM content (S1, S2) and three values of initial H 2 O 2 concentration (10, 20 and 30gL  − 1 ) In Fig. 1 the hydrogen peroxideconsumed   X  H 2 O 2  vs. time is shown.The data in Fig. 1 indicate that, for the same value of the initialH 2 O 2  concentration, higher hydrogen peroxide decomposition isobtained if the concentration of SOM increases. Under neutral pHconditions, hydrogen peroxide is decomposed more slowly in S2(SOM=10%) than in S1 (SOM=15.1%).Ontheotherhand,itcanbepointedoutfromFig.1thatasymp-totic values for hydrogen peroxide decomposition are reached. Foragivensoil,thevalueofthisasymptoteincreasesastheinitialH 2 O 2 dosage does. This fact, not previously described in literature, couldbeexplainedifthecompoundsreactingwiththehydrogenperoxideare totally oxidized before this oxidant is fully consumed.The asymptote in the H 2 O 2  decomposition was not found foracidic pH and using iron species (added or naturally occurring insoils) [3]. This could be explained because at these conditions, thehydrogenperoxidedecompositionoccursbyadifferentmechanismthat at neutral pH.In Fig. 2 are shown the hydrogen peroxide consumptions incontact with S1 and S2 at [H 2 O 2 ] o =20gL  − 1 . They are comparedto consumption of soil samples with SOM loss by ignition at thesame hydrogen peroxide concentration (runs 2–5–7–8 in Table 2).The hydrogen peroxide decomposition is more slowly when theSOM content is throughout removed by ignition. Low asymptoticconversion is obtained with calcinated soilsData shown in Fig. 2 indicate for each soil that the H 2 O 2  isdecomposed also by the inorganic matter. Moreover, it can besupposed that the main contribution to the hydrogen peroxidedecomposition could be related to the soil carbonate content. Infact, soil S2 has a lower CaCO 3  content (7.3%) than S1 and loweredH 2 O 2  consumptionisobtainedfortheincineratedsoilS2,asshownin Fig. 2b. However, data obtained with soils S1 and S2 before andafter calcination should be carefully compared while the SOM canstrongly modify the accessibility and interaction of the hydrogenperoxide to the mineral surface. Therefore, the contribution of theSOM to the hydrogen peroxide decomposition can not be analyzedas the difference obtained before and after calcination.  3.2. Change of SOM content after oxidation InFig.3,weightchangesbyTGAmeasurementsbeforeandaftertreatment ( t  =60min) of soils used in runs 2 and 5 in Table 2 are Fig.3.  RelativemasslossbyTGAofthesoilsS1(a)andS2(b)withandwithoutH 2 O 2 treatment. Reaction time=60min, [H 2 O 2 ] o  =20gL  − 1 . shown ([H 2 O 2 ] o =20gL  − 1 ). The SOM initial and by treatment withhydrogen peroxide has been calculated from the relative mass dif-ference between 150 and 550 ◦ C in the two curves obtained witheach soil (Fig. 3a and b). It has been obtained that the SOM ini-tially present in soil S1 changes from 151 to 164mg SOM g soil − 1 ,being changes for S2 from 100 to 113mg SOM g soil − 1 Therefore,the total SOM content is slightly modified after oxidation. Theseresults are consistent with the data obtained by incineration: S1changes from 155 to 173mg SOM g soil − 1 and S2 changes from 91 to98mg SOM g soil − 1 . This weak weight increase could be attributed tothe oxygen introduced by the oxidation of the srcinal SOM. TheSOM is then oxidized but not mineralized.Therefore, having into account the results from TGA and theasymptotic values for hydrogen peroxide decomposition in Fig. 1the following reaction is proposed to describe the oxidation of theSOM and decomposition of hydrogen peroxide:H 2 O 2 +  SOM  →  SOM OX + Products (16)Moreover, Eq. (16) describing the decomposition of hydrogenperoxide by SOM could be derived if some of the radical reactionsin Eqs. (1)–(15) are lumped (i.e. Eqs. (1) and (8)). An empirical sto- ichiometric coefficient    is used to do this.To explain the asymptotic value of hydrogen peroxide conver-sion in Fig. 1 the SOM in the Eq. (16) could acts as limiting reagent. When the SOM surface sites are exhausted, the hydrogen peroxideis not more decomposed and reaches a constant value.  3.3. Decomposition kinetic of H   2 O  2 The data of the runs conducted in the batch system at pH 7 inthepresenceof0.5gofsoilsamplespresentedinFig.1wereusedtodiscriminate the kinetic model. According to Eq. (16), not only theH 2 O 2  but also the SOM must be included in the kinetic equation   A. Romero et al. / Journal of Hazardous Materials 170 (2009) 627–632  631  Table 3 Parameters values estimated by fitting data obtained in the hydrogen peroxide decomposition in soils S1 and S2 separately. [ k ]=(g soil  Lg SOM − 2 min − 1 ) [  ]  =  g SOM  g soil − 1  g H 2 O 2  L  − 1  − 1 .Experimental data fitting Parameter Value Standard error Confidence interval SQR Runs 1, 2 and 3  k  1.07 × 10 − 2 7.19 × 10 − 4 1.21 × 10 − 2 2.96 × 10 − 1   1.19 × 10 − 2 3.59 × 10 − 4 1.26 × 10 − 2 Runs 4, 5 and 6  k  1.39 × 10 − 2 6.85 × 10 − 4 1.53 × 10 − 2 1.31 × 10 − 1   0.84 × 10 − 3 2.59 × 10 − 4 1.03 × 10 − 2  Table 4 Parameters values estimated by fitting data obtained in the hydrogen peroxide decomposition in soils S1 and S2 simultaneously. [ k ]=(g soil  Lg SOM − 2 min − 1 ) [  ]  =  g SOM  g soil − 1  g H 2 O 2  L  − 1  − 1 .Experimental data fitting Parameter Value Standard error Confidence interval SQR Runs with S1 and S2  k  1.24 × 10 − 2 6.35 × 10 − 4 1.41 × 10 − 2 6.05 × 10 − 1   1.11 × 10 − 2 2.64 × 10 − 4 1.20 × 10 − 2 and the asymptotic values in Fig. 1 must be explained. To do this,the following second-order kinetics expression is proposed: − dn H 2 O 2 W  SOM dt   = r  H 2 O 2  = kC  H 2 O 2 C  SOM  (17)where  k  is the kinetic constant,  C  SOM  and  C  H 2 O 2  are the SOM con-centration and the hydrogen peroxide concentration, respectively;and the parameter  W  SOM  is the organic matter mass initially con-tainedforeachsoil.InEq.(17)itissupposedthathydrogenperoxidedecomposition occurs in a heterogeneous way as was previouslyfound elsewhere [24]. Moreover, blank runs for hydrogen peroxide decomposition carried out at neutral pH in absence of soil showa negligible decomposition of the hydrogen peroxide and confirmthe heterogeneous mechanism.By introducing the organic slurry density,  W  SOM / V  L  , in Eq. (17)the following expression is obtained: − dC  H 2 O 2 dt   = kW  SOM V  L C  H 2 O 2 o (1 −  X  H 2 O 2 ) C  SOM  (18)Having into account Eq. (16) the stoichiometric relationshipbetween  C  SOM  and  C  H 2 O 2  results: C  SOM  = C  SOMo − C  H 2 O 2 o  X  H 2 O 2  (19)being    and empirical stoichiometric coefficient.By introducing Eq. (19) in Eq. (18) the following expression is obtained: dX  H 2 O 2 dt   = kW  SOM V  L  C  H 2 O 2 o (1 −  X  H 2 O 2 )  C  SOMo C  H 2 O 2 o − X  H 2 O 2   (20)The collected experimental   X  H 2 O 2  vs. time curves were fittedto Eq. (20). Non linear regression by using a Marquardt algorithmhas been applied in the fitting procedure. First, kinetic constants  k and stoichiometric parameter    have been estimated fitting eachsoil separately and parameters values obtained for soils S1 and S2are summarized in Table 3. Residual sum of squares (SQR) for eachsoil have been calculated by comparison of experimental data tothosepredictedbythecorrespondingkineticmodel.Standarddevi-ation and confidence interval values of the estimated parametersare also provided in Table 3. As can be seen a satisfactory fitting isobtained.AsdeducedfromTable3the k and  valuesobtainedforeachsoilarequitesimilar,validatingtheapproachinEq.(20).Therefore,dataobtained by using S1 and S2 have been simultaneously fitted to Eq.(20) and the estimated and statistical parameters values obtainedare summarized in Table 4. Predicted   X  H 2 O 2  using the estimatedparameters from Table 4 are shown as lines in Fig. 1. As is shown in Fig. 1, the experimental and simulated data are plotted as pointsand lines, respectively. As can be seen, even using a unique kineticparametersforthedifferentsoilsandhydrogenconcentrationused,agoodagreementisnoticedinallcases,forthewholeinitialhydro-genperoxideconcentrationintervalused(10–30gL  − 1 )andforbothsoils (S1 and S2). Therefore, the kinetic model in Eq. (18) with thestoichiometric relationship in Eq. (19) is able to explain quite wellthe data obtained. 4. Conclusions Soil slurries were investigated for hydrogen peroxide decom-position at neutral pH. Soils with higher SOM content increasedthe hydrogen peroxide decomposition rate. Moreover, a slightSOM increase was found for S1 and S2 before and after thetreatment. It could be due to the introduction of oxygen in thesrcinal SOM creating oxidized surface sites. This fact, togetherwith the asymptotic values found for the hydrogen peroxide con-version, could be explained by using the second-order kineticmodel here proposed. The SOM reacts with the hydrogen perox-ide being totally oxidized (not mineralized) before this oxidant isfully consumed at the conditions tested. The hydrogen peroxidedecomposition was observed to follow a second-order kinetic. Akineticconstantaround1.24 × 10 − 2 g soil Lg SOM − 2 min − 1 wasfound.The empiric stoichiometric coefficient used to relate the SOM andhydrogen peroxide changes,   , was estimated by data fitting as0 . 0111  g SOM g soil − 1  g H 2 O 2  L  − 1  − 1 .On the other hand, the results of this research show that hydro-gen peroxide as oxidant reagent for in situ remediation does notsignificantlychangetheSOMtotalcontentalthoughcouldmodifiedits oxidation state.The high concentrations of hydrogen peroxide requirementsfound in literature for in situ oxidation of sorbed contaminants bymodified Fenton’s reagent could be related to the SOM-hydrogenperoxide interaction consuming this reactant.  Acknowledgements The authors acknowledge financial support for this researchfrom the Spanish MEC provided throughout project CTM2006-00317. References [1] H.-W. Sun, Q.-S. Yan, Influence of Fenton oxidation on soil organic matter andits sorption and desorption of pyrene, J. Hazard. Mater. 144 (2007) 164–170.[2] P.K.C. Kakarla, R.J. Watts, Depth of Fenton-like oxidation in remediation of sur-face soil, J. Environ. Eng. 123 (1997) 11–17.
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