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Treatment of petroleum hydrocarbons contaminated soil by Fenton like oxidation
Chemosphere 232 (2019) 377e386
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Treatment of petroleum hydrocarbons contaminated soil by Fenton like oxidation H. Ouriache a, J. Arrar a, *, A. Namane a, F. Bentahar b a Laboratoire des Sciences et Techniques de l’Environnement (LSTE), Ecole Nationale Polytechnique, Avenue Hassen Badi, BP 182 El Harrach, 16110, Algiers, Algeria b Laboratoire des Ph enom enes de Transfert, Facult e de G enie M ecanique et G enie des Proc ed es, Universit e des Sciences et de la Technologie Houari Boumediene, BP 32 El Alia Bab Ezzaouar, 16111, Algiers, Algeria
h i g h l i g h t s FL oxidation without pH modification for aged petroleum hydrocarbons contaminated soil. Parametric study and Statistically designed experiment on FL oxidation performances. H202, key factor affecting TPHS removal efficiency with important interaction effects H2O2-Fe, Fe-EDTA and H2O2-Fe-EDTA. Endogenous iron exhibits high catalytic potential to activate H2O2 in presence of EDTA.
a r t i c l e i n f o
a b s t r a c t
Article history: Received 30 January 2019 Received in revised form 5 May 2019 Accepted 7 May 2019 Available online 10 May 2019
Experimental tests were carried out in solid phase reactors on a microcosm scale, to removal old petroleum pollution by Fenton like oxidation process. In order to optimize the process, parametric study and statistically designed experiment have been undertaken by considering the amount influence of hydrogen peroxide (H2O2), endogenous and zero-valent iron (Fe) and ethylene diamine tetraacetic acid (EDTA) as chelating agent. The measurement of residual total petroleum hydrocarbons for different H2O2/Fe molar ratios and pH in the vicinity of neutrality highlighted oxidation rates ranging between 29.0 and 39.3%. The Fenton like (FL) oxidation was optimal for H2O2/Fe molar ratio of 15/4. The use EDTA led to result up 72.2% for H2O2/ total Fe/EDTA molar ratio of 15/4/4 after 48 h of treatment. The statistical analysis of data by factorial design, has allowed the modeling of Fenton like process performances in the operating domain. It showed that hydrogen peroxide amount, interaction effects of oxidant-catalyst, catalyst-chelating agent, and oxidant-catalyst-chelating agent, were the influential parameters. Moreover, these results suggest that endogenous iron could be used as a source of iron in the presence of the chelating agent to activate FL oxidation. A better accuracy (80.0%) was obtained by statistical analysis for H2O2/endogenous Fe/EDTA molar ratio of 20/1/1. © 2019 Elsevier Ltd. All rights reserved.
Handling Editor: X. Cao Keywords: Fenton-like Soil remediation Petroleum hydrocarbons EDTA Oxidation
1. Introduction The pollution of soils in Algeria constitutes major problem in view of the number of contaminated sites for years even decade, potential hazards that threaten environment and human health and the need to treat and/or restore them. Petroleum oils and their derivatives, resulting from oil industry activities, accidental discharges, leakages from underground storage tanks and ruptures of
* Corresponding author. E-mail address: [email protected] (J. Arrar). https://doi.org/10.1016/j.chemosphere.2019.05.060 0045-6535/© 2019 Elsevier Ltd. All rights reserved.
pipelines, are the main source of pollution. 1.1. Different treatment techniques can be applied … Bioremediation is considered as an environmental and economic approach for the treatment However, the presence of recalcitrant and/or toxic substances (Kulik et al., 2006), the constraints of deadlines (Kulik et al., 2006) and residual levels of pollutants (Usman et al., 2012b) require fast and effective treatments such as combining chemical oxidation with bioremediation. Indeed, advanced oxidation processes are a good alternative for
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the remediation of soils subject to old contamination with toxic and persistent organic pollutants (Cheng et al., 2016a; Huang et al., 2017) and have the advantages to be rapid and relatively efficient (Goi et al., 2006; Ferrarese et al., 2008). These processes can be used until disappearance of toxicity and/or generation of more biodegradable and/or harmless by-products (Kulik et al., 2006; Mater et al., 2007; Silva-Castro et al., 2013; Valderrama et al., 2009; Venny et al., 2012). Among these processes, Fenton treatments are ones of the best options (Yap et al., 2011), because of their high potential to treat contaminated soils their simplicity to be implemented (Ferrarese et al., 2008; Venny et al., 2012). They use the high reactivity of the hydroxyl radical (OH ) generated by the Fenton reaction and able to oxidize almost all organic contaminant types (Cheng et al. 2016b; Gan et al., 2013; Lu et al., 2010b). However, Its application is limited by the optimum pH very acidic (3) to inhibit iron precipitation (Sirguey et al., 2008) and its negative impacts on soil fate. In addition, Zhou et al. (2009) showed that continuous iron addition was necessary to achieve complete degradation of target contaminants. To overcome these drawback, Fenton like (FL) oxidation has been developed using catalysts such as, mineral iron oxides (ferrihydrite (Fe2(OH)6), hematite (Fe2O3) or goethite (a-FeOOH)) (Ferrarese et al., 2008) or zero-valent iron, for an effective degradation of organic contaminants in the range of neutral pH (Usman et al., 2012b). Matta et al. (2007) and Xue et al. (2009) noticed that mineral oxides of Fe(II), such as magnetite (mixture of Fe(II) and Fe(III), are more effective catalyst compared to mineral Fe(III) oxides such as hematite, goethite and ferrihydrite. The application of magnetite as a catalyst to activate hydrogen peroxide resulted in crude oil removal efficiencies of up to 80%, while soluble Fe2þ species generated weak efficiencies of 10e15% (Usman et al., 2012b). The addition of chelating agents, such as catechol, gallic acid, oxalic acid, ethylene diamine tetracetic acid, is generally recommended to enhance the FL treatment efficiency and to prevent iron precipitation at natural soil pH (Xu et al., 2011; Venny et al., 2012 Romero et al., 2011). According to Seibig and Van Eldik (1997) and Viisimaa et al. (2013), chelating agents promote the formation of hydroxyl radicals or other oxidants and the production of dioxygene and possibly hydrogen peroxide.). This work deals with the soil removal of petroleum hydrocarbons in the case of an old pollution by FL oxidation without pH modification and the determination of the optimal conditions. The effects of hydrogen peroxide (H2O2), endogenous and zero valent iron (Fe), and ethylene diamine tetracetic acid (EDTA) are studied. The application of an experimental design was used to assess and optimize the potentially influential parameters on the removal of petroleum hydrocarbons soil and the modeling of FL process in the case of the studied soil.
2. Material and methods 2.1. Reagents All chemical reagents and solvents used were of analytical grade and used as received without purification. Deionized water (GFL inmbH D-30938 Burgwedel, 2008) was used for all prepared solutions. The powder of iron was purchased from Chemopharma with purity of 98.5%. It was characterized as micro-valent iron with an average of particle size of 37 mm (Mastersizer2000, Malvern Instruments) and Brunauer-Emmet Teller (BET) surface area of 6.78 ± 0.03 m2/g (Micrometrics ASAP, 2010V5.02H).
2.2. Soil Studied soil was sampled from a polluted site by petroleum hydrocarbons since the 1990s and located at 36 11026, 01 North, 3 11008, 0 East in Dar El Beida, the east of Algiers. The soil samples were collected, according to standard method, up to 20 cm a depth; air dried at room temperature, sieved at 0.8 mm, and homogenized according to the quartering method (twice redone). The pretreated soil was then stored at 4 C in the dark until use. 2.3. Soil characterization The main physic-chemical parameters of soil were analyzed according to standard methods. Particle size distribution was determined by sieving and sedimentation after destruction of the organic matter with hydrogen peroxide and dispersion with sodium hexametaphosphate (Mathieu and Pieltain, 2003). The soil pH was determined using pH meter (Hanna) with a soil deionized water ratio of 1/5 w/v after 1 h stirring. The moisture content was determined by drying at 105 C up to constant weight. Organic matter and organic carbon were determined respectively by calcinations at 550 C for 4 h and by digestion with potassium dichromate in acidic media and titration according to Anne's method (Mathieu and Pieltain, 2003). Total iron was determined by flame atomic absorption spectrophotometer (Agilent 240 Z AA) after calcination followed by aqua regal (4:1 v/v concentrated hydrochloric acid to concentrated nitric acid) digestion according to Mc Grath and Cunliffe (1985). All measures of the above parameters were done in triplicate and the average of the three independent measures was reported. Quantification of oil pollution levels was performed from the determination of total petroleum hydrocarbons (TPHs) by the gravimetric method. 1 g of contaminated soil sample was mixed and crushed with anhydrous sodium sulfate according to a mass ratio of 4/5 and extracted with dichloromethane (DCM) by sonication for 15 min. After centrifugation, the extract was removed and the process repeated twice, the first with 12 mL and the second with 6 mL of DCM; total extract was concentrated at 40 C (rotary evaporation) and then weighed. The TPHs content was revised to dry weight. The variation of the reproducibility of TPHs measure was determined by duplicating sampling and the average result was reported. 2.4. Soil microcosm experiments Experiment essays were carried out on a microcosm scale in solid phase reactor at lightless and ambient temperature during 48 h. 150 g of contaminated soil samples to be treated were introduced in 250 ml Erlenmeyer and placed on an orbital vibrating shaker at 150rd/min. These samples were previously sterilized with 0.2% mercury chloride (Nam et al. 2001) and sprinkled with deionized water to ensure a moisture content of 25%. Removal of soil TPHs was carried out by FL oxidation without adjustment of pH, the hydrogen peroxide being catalyzed by endogenous iron and by both endogenous and micro zero valent iron. In a first part, each reactor received different quantities of hydrogen peroxide according to H2O2/Fe molar ratios ranging from 1/1 to 20/1 to reveal hydrogen peroxide influence on TPHs removal. In a second part, each reactor received the same amount of hydrogen peroxide, the content being fixed at 4.5 mol H2O2/kg of dry soil, and different quantities of iron powder according to various molar ratios of H2O2/Fe going from 15/1 to 15/8 in reference to both endogenous and exogenous iron. A third series of experiments focused on the influence of ethylene diamine tetraacetic acid
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addition according to different H2O2/Fe/EDTA molars ratios by considering optimal quantities of hydrogen peroxide and total iron. For all the experiments, FL oxidation was initiated with the introduction of H2O2 and its mixing with soil and all other additives. The TPHs content, the pH and the moisture content were periodically monitored for 48 h. The latter was maintained between 25 and 30%. The oxidation reaction was stopped by addition of sodium sulphite (Valderrama et al., 2009) to monitor the residual TPHs from the treated soil. 2.5. Process optimization analysis Factorial experiment design was used to determine main effects of H2O2, total iron and EDTA contents, as well as interaction effects between them to optimize and predict Fenton-like process. The experiments were arranged according to a factorial design with three factors on two distinct levels (23). Table 1, presents the limits of variation of the independent variables. The low, centre and high levels of each independent factor were designed as 1, 0, þ1 level respectively. 3. Results and discussion
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and Cassidy, 2014).
Fe0 þ H2 O2 /Fe2þ þ 2OH Fe2þ þ H2 02 /Fe3þ þ OH þ HO
(1a)
(1b)
This increase was less significant with iron addition. Beyond 1.2 mol/kg dry soil of iron (H2O2/Fe ¼ 15/4), the recorded values of pH were lower (˂7) than the natural pH (Fig. 1b). This diminution could be associated to hydrogen peroxide stabilization (Jung et al., 2013; Vicente et al., 2011). In the case of EDTA (Fig. 1c), the increase in pH was moderate, probably due to the generation of hydrogen peroxide in the medium and hydroxide ions resulting from the reaction of EDTA with iron (Zhou et al., 2009). Sherwood and Cassidy (2014) recorded similar values of pH regardless of the presence of EDTA. Goi et al. (2006); Usman et al. (2012a) and Sherwood and Cassidy (2014) did not observe soil pH changes during FL oxidation pretreatment while Vicente et al. (2011) observed a decrease in soil pH (˂7) initially ranging between 7 and 8.2. Soil acidification would be mainly allotted to a modification of the surface charge or the redox potential of mineral surface by the precipitation of cations (Vicente et al., 2011).
3.1. Soil characteristics 3.3. And total iron/EDTA (1c) The main results of the soil characterization are reported in Table 2. The soil particle size analysis (Table 2) revealed a loam texture with 15% of clay, 35.75% of silt and 49.25% of sand. Permeability measurement highlighted a permeable soil in favor of best transfer between the different phase and good oxygenation. Soil pH was in the range for the development of microbial population and the growth of hydrocarbons degrader microorganisms (Gray et al., 2000) in the event of biological treatment. Organic matter and TPHs contents were respectively of 6.0% and 3.0%. The total iron content of 16.8 g/kg is significant regarding to Fenton oxidation. 3.2. Fenton-like oxidation treatment 3.2.1. pH Addition of FL reagents and EDTA affected little the initial pH (Fig. 1). In general, FL reaction was accompanied by increases in pH in a field of 7.2e7.9. The increase in pH with hydrogen peroxide addition (Fig. 1a) could be allotted to the hydroxide ion release according to reactions.(1) (Bergendhal and Thies, 2004; Sherwood
Table 1 Factors and coded levels for the experiment design. Independent Variables (mol./kg dried soil)
Factors
H2O2 Iron EDTA
X1 X2 X3
Coded level 1
0
þ1
0.30 0.30 0.30
3.15 1.35 1.35
6.00 2.40 2.40
3.3.1. Total petroleum hydrocarbons FL treatment efficiency depends on soil matrix (Kulik et al., 2006; Sun and Yan, 2008), and age and extent contamination, and consequently requires the determination of optimum conditions for efficient application. Hydrogen peroxide (H2O2) influence on TPHs removal without iron addition was studied for different contents ranging from 0.3 to 6.0 mol H2O2/kg dry soil. The results of residual TPHs (Fig. 2a) highlighted the catalytic potential of endogenous iron with oxidation yields of soil petroleum hydrocarbons between 7.3 and 29.0% after 48 h of treatment. Indeed, several studies showed that iron minerals naturally present in soil exhibit different catalytic activities depending on the surface charge of iron or its oxidation state under pH conditions ranging from 4 to 9 (Kwan and Volker, 2003). Yeh et al. (2003) reported 78% of sorbed TCE reduction by 3% of H2O2 in the case of aquiferous sand containing 2.01 g of extractable iron/kg sand. Soil TPHs removal increased with H2O2 amount up to 29%, for then decrease beyond an H2O2 content of 4.5 mol/kg dry soil. Similar tendencies were reported in the literature (Flotron et al., 2005; Goi et al., 2006; Watts et al., 2002). Excess of H2O2 reduced TPHs oxidation effectiveness and inhibited FL process for H2O2/Fe molar ratio of 20/1. This inhibition could be the result of a significant consumption and/or scavenging of OH radicals by H2O2 excess (Yap et al., 2011) and the formation of less reactive HO2 radicals as presented by reactions (2) and (3) (Watts et al., 2002).
HO þ H2 O2 /H2 O þ HO2
(2)
HO þ HO2 /H2 O þ 02
Table 2 Soil chemical characteristics. pH
7.21 ± 0.11
Texture
Loam
Humidity (%) Organic Matter (%) Organic Carbon (%) BET Surface Area (m2.g-1) TPHs (g.kg-1) Total Iron (Fe) (%)
2.46 ± 0.06 5.97 ± 0.16 2.08 ± 0.01 24.42 ± 0.12 30.51 ± 0.46 1.68 ± 0.10
Clay (%) Loam (%) Sand (%) d60 (mm) Cu (D60/D10) Permeability (m.s-1)
15.00 ± 0.11 35.75 ± 0.25 49.25 ± 0.50 160 10.66 5.56 10-5
(3)
Furthermore, too high doses of H2O2 generate the decomposition of the latter and limit the production of OH radicals and other
radical or non-radical species such as HO2 ; O2 and HO 2 , (Xu et al., 2011). According to Walling (1975), an excess of H2O2 could compete with organic substances with respect to OH radicals, thus reducing their efficiency and the oxidation of pollutants. The optimal amount of H2O2 for an effective oxidation varies
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Fig. 1. pH variations according to the H2O2 dose (1a), total iron dose (1b).
according to organic compounds reactivity with respect OH radical. Many studies refer to an optimal molar ratio H2O2/Fe of 10/1 between hydrogen peroxide and iron (Goi and Trapido, 2004; Kulik et al., 2006; Sun and Yan, 2008; Valderrama et al., 2009; Usman et al., 2012a). The maximum removal rate of TPHS of 29% was
obtained for H2O2/Fe molar ratio of 15/1 corresponding to H2O2 content of 4.5 mol/kg dry soil. This result was in good agreement with those of further related studies which provide optimal values of H2O2/Fe molar ratios between 5/1e25/1 (Jorfi et al., 2013). Valderrama et al. (2009) recorded a diminution in total PAHS removal rate of 80% when H2O2/Fe2þ molar ratio increases from 10/ 1 to 40/1. Xu et al. (2011) observed a maximum elimination of TPHS of 23% and 24% for 42/1 and 210/1 M ratios respectively. Lu et al. (2010b) obtained a maximum removal efficiency of total dichloromethane-extractable organics with H2O2/Fe3þ molar ratio of 300/1, the H2O2 dose being fixed at 0.49 mol/kg dry soil. Usman et al. (2012b) reported that the application of magnetite as a catalyst to activate hydrogen peroxide provided high efficiency (80%) of crude oil contaminated soil remediation for H2O2/Fe molar ratio of 10/1. Under optimized conditions, Watts et al. (2002) achieved 85% of benzo[a]pyrene mineralization using 15 M H2O2 catalyzed by endogenous iron and reported for FL treatment, that the optimized H2O2 contents were normally higher than 5 M. Goi and Trapido (2004) reported that oxidation of PAHscontaminated soil with high H2O2 contents was effective even for aged polluted soil and resulted in efficiencies between 40 and 86%. Finally, highly hydrophobic compounds generally require high H2O2 doses while less soluble compounds can be degraded with relatively weak doses (Villa et al., 2008). Although Yap et al. (2011) reported that FL reaction with iron oxides gives high degradation efficiency at near neutral pH between 7.0 and 8.0 and that the oxidation of sorbed contaminants was possible with high doses of H2O2 (Watts et al., 2002; Quan et al., 2003), the TPHs oxidation efficiency in our case did not exceed 29%. In view of relatively weak efficiencies (29%) obtained with endogenous iron, the TPHs removal from the studied soil requires more significant amounts of iron to be determined. For that purpose, the zero valent iron (ZVI) powder was used and H2O2 content of 4.5 mol/kg dry soil was considered as the optimum value for the further essays. In general, the increase in iron content improved the oxidation rate of organic pollutants due to the increase in the number of active sites to catalyze H2O2 and the production of more OH radicals (Yap et al., 2011). The addition of iron (Fig. 2b) generated a light increase in TPHs removal efficiency to reach a maximum of 39.3 ± 3.8% for H2O2/Fe molar ratio of 15/4, by considering total iron, for then decrease. It should be noted that for H2O2/Fe molar ratios greater than 15/ 4, red deposits, probably iron hydroxides, were observed and could be responsible for the inhibition of FL oxidation. Benatia et al. (2009) and Henz et al. (2002) observed the same phenomenon with iron based catalyst for pH > 5. Furthermore, excess of iron also causes unproductive consumption of hydroxyl radicals (Lu et al., 2010a) and undesirable side reactions which increase the scavenging of OH radicals (Yap et al., 2011). The addition of iron improved TPHs removal efficiency by only 37.4% compared with endogenous iron alone. This improvement, not significant, could be allotted to performances of micro-zerovalent iron (mZVI) used. It could also be awarded to the sorption of Fe species on organic compounds in the soil, which was more significant as the pH gets higher (Catrouillet et al., 2014). This makes iron species less available for the Fenton reaction activation. In addition, pollution aging and organic matter are all factors that can limit the availability of contaminants to Fenton's reagents, and promote the sequestration of OH radicals as shown by previous work of Sun and Yan (2008). In order to improve performances of FL oxidation process and to promote hydroxyl radicals formation or other oxidants and
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381
40 [Fe]=0.3mol/kg dry soil 35
0H
24H
48H
TPHs (g/kg dry soil)
30 25 20 15 10 5 0 01:01
05:01
10:01
11:01 12:01 13:01 (H 2O2/Fe)molar ratio
14:01
15:01
20:01
40 [H 2O2]=4.5mol/kg dry soil 35
0H
24H
48H
TPHs (g/kg drY soil)
30 25 20 15 10 5 0 15:01
15:02
15:03 15:04 (H 2O2/Fe)molar ratio
15:06
15:08
Fig. 2. a Temporal TPHs evolution according to H2O2 level variations. b: Temporal TPHs evolution according to iron level variations. c: Temporal TPHs evolution according to EDTA level variations.
consequently the TPHs soil removal, we have used ethylene diamine tetraacetic acid (EDTA) according to different H2O2/Fe/ EDTA molar ratios. Results (Fig. 2c) showed that EDTA led to significant increase in TPHs removal, independently of iron addition and thus, the performance of FL oxidation. EDTA addition contributed to an increase of 80.8% (without Fe addition) and 83.6% (with Fe addition) for respective H2O2/Fe/EDTA molar ratios of 15/1/4 and 15/4/4 in comparison with these last ones of 15/1/0 and 15/4/0. The highest TPHs removal efficiencies of 72.2% were observed for H2O2/ Fe/EDTA molar ratios of 15/4/4 and 15/4/8 and highlight an optimal Fe/EDTA molar ratio of 1/1 to be implemented. This last ratio corroborates the results of further works in the field of soil remediation by FL oxidation and is especially recommended for hydrophobic organic contaminants (Xue et al., 2009; Lu et al., 2010a).
The increase in soil TPHs removal efficiency with EDTA addition could be awarded to changes in the surface charge or the oxidation state of iron leading to an improvement of catalytic potential of this last and/or to iron complexes formation in favor of catalyst availability (Vicente et al., 2011). This increase could also result from the generation of H2O2 in the medium according to Zhou et al. (2009) and/or a reduction of its assimilation. Indeed, EDTA greatly decreased H2O2 uptake, probably due to the competition between chelating agent and H2O2 for surface sites on endogenous iron according to Jia et al. (2018). Decrease in H2O2 decomposition rates was also observed with EDTA use at neutral pH (Xue et al., 2009). Jia et al. (2018) reported that addition of EDTA enhanced TCE degradation in sand columns with high content of magnetite (7.0%) and inhibited it with small content of magnetite (0.5%). Lu et al. (2010a) obtained the best results of 38.3% for H2O2/Fe3þ molar
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40 [H 2O2]/[Fe]/[EDTA]
35
15/4/00
15/4/04
24 Times (hours)
27
15/4/08
15/1/04
TPHs (g/kg dry soil)
30 25 20 15 10 5 0 0
3
48
Fig. 2. (continued).
3.4. Factorial design The experimental tests were organized and carried out according to an experiment matrix, written in coded variables as shown in Table 3 to model the TPHS removal (response Y) in the previously established study domain. For a statistical significance evaluation of the effects and interactions, 3 centre points were carried out. TPHS removal efficiencies by FL oxidation, were adjusted with a polynomial model of the 1st order connecting the response Y to variables Xi¼1,2,3 given by equation (4). The model coefficients were determined using JMP 8.0 statistical analysis software.
Table 3 Experimental results of 23 full factorial design. Experimental number
Point type
X1
X2
X3
Response Y(%)
01 02 03 04 05 06 07 08 09 10 11
Factorial Factorial Factorial Factorial Factoria Factorial Factorial Factorial Centre Centre Centre
1 þ1 1 þ1 1 þ1 1 þ1 0 0 0
1 1 þ1 þ1 1 1 þ1 þ1 0 0 0
1 1 1 1 þ1 þ1 þ1 þ1 0 0 0
18.80 80.01 35.10 70.10 36.10 79.21 31.76 75.11 50.98 50.13 50.45
Y ¼ 51:62 þ 24:10X1 1:49X2 þ 1:01X3 1:98X1 X2 þ 0:02X1 X3 3:12X2 X3 þ 4:54X1 X2 X3 (4) Where variables Xi¼1,2,3 are the coded values of the contents of hydrogen peroxide (H2O2) (3.15 þ 2.85X1 (mole/kg dry soil)), total iron (Fe) (1.35 þ 1.05X2 (mole/kg dry soil)) and ethylene diamine tetraacetic acid (EDTA) (1.35 þ 1.05X3 (mole/kg dry soil)) respectively. 3.4.1. Regression models and statistical testing The plot of experimental versus predicted responses (Fig. 3) showed square correlation coefficients R2 and adjusted R2 respectively equal to 0.999 and 0.996. Only 0.4% of the total variance could not be explained by the used model. The high values of these two coefficients and their
90 80
Experimental Response
ratio of 200/1, a slurry pH of 7, the H2O2 dose and EDTA/Fe molar ratio being fixed at 0.49 mol/kg dry soil and 1/1 respectively. Viisimaa et al. (2013) highlighted that EDTA addition not only chelates and mobilizes the metals from soil but also substantially increases the soil contaminant availability, thus improving contaminants oxidation. The microcosmal scale (unsaturated soil) test results revealed, in addition to the effectiveness and the feasibility of the FL oxidation process in the case of an old soil pollution, that Fenton reagents and EDTA influence the oxidation effectiveness of soil TPHS with synergistic and antagonistic effects in the study domain from where the relevance to optimize the process.
70 60 50 40 30 20 10 10
20
30
40 50 60 Estimated Response R2=0.9961
70
80
Fig. 3. Comparison of the estimated and experimental response.
90
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significant concordance ensure a very good descriptive quality of the model. The regression coefficients significance in equation (4) was verified by the Student t-test application. An effect will be considered if the associated absolute t-value is greater than t-critic equal to 3.182 (Student table) for 95% confidence level. Another method is to consider the probability value (p-value) of each model term closer to zero and which must be less than or equal to the threshold p of 0.05. These tests, from the review of tvalues and p-values (Table 4) highlighted 3 non significant coefficients (a2, a3 and a13) for Y response. These results were also confirmed by the Pareto Chart test (Fig. 4), which shows each effects and interactions estimated by decreasing order of importance, where the vertical line defines 95% of the confidence interval. It arises from the different significance tests, that only the variable X1 and the interactions X1X2, X2X3, and X1X2X3 affect significantly the soil TPHS removal efficiency (response Y). As a result, the model was adjusted by considering only the influential linear and interaction effects (equation (5)).
Y ¼ 51:62 þ 24:1OX1 1:98X1 X2 3:12X2 X3 þ 4:54X1 X2 X3 (5) To check the significance of the model variables retained, a Fisher test was established. Analysis of variance (ANOVA) showed a fairly high mean square of regression compared to the main square of residues (Table 5) and consequently a Fisher value (F ¼ 111.19) mush higher than the critical one (F0.05; 7; 3 ¼ 8.89). This means a good adequacy of model regression to experimental data at a 95% confidence level. 3.4.2. Average effects of the factors and interactions Analysis of the adjusted model given in equation (5) indicated that the amount of H2O2 (X1) is the key factor affecting the soil TPHS removal efficiency (response Y) since its coefficient is the higher modulus. In addition, its positive sign means that TPHs removal efficiency increases significantly with H2O2 content. These results corroborate the experimental results obtained in the first stage while varying H2O2 dose only. Conversely, iron content (X2) was found statistically insignificant for the response Y probably due to the capacity of endogenous iron (0.3 mol/kg dry soil) to catalyze H2O2 and to generate maximum removal of soil TPHs for H2O2 content of 6.0 mol/kg dry soil. These results corroborate works of Kwan and Volker (2003), Goi et al. (2006), Kulik et al. (2006), Xue et al. (2009), Yap et al. (2011), Jung et al. (2013), which evidenced that iron oxides naturally present in soil can catalyze H2O2 and promote organic contaminants oxidation under pH in the field of neutrality. Effects of iron (X2) and EDTA (X3) contents were not directly influential but were through interactions effects at the 95% confidence level as shown in Fig. 5. The plots of interaction effects
Table 4 The model coefficients analysis of the Y response. Coefficients a0 a1 a2 a3 a a a a a
12 13 23 123
values 51.622 24.096 1.493 1.008 1.983 0.018 3.116 4.543
Standard deviation 0.403944 0.473666 0.473666 0.473666 0.473666 0.473666 0.473666 0.473666
Values which respond to significant tests.
t-value a
127.80 50.87a 3.15 2.13 4.19a 0.04 6.58a 9.59a
p-value <0.0001a <0.0001a 0.0511 0.1231 0.0248a 0.9709 0.0071a 0.00241a
383
Terms H2O2 H2O2*ZVI*EDTA H2O2*ZVI EDTA ZVI*EDTA H2O2*EDTA ZVI Fig. 4. Pareto Chart for standardized effects.
evidenced interaction existence between two factors, when the two lines of levels 1 and þ1 are not parallel. The parallel lines indicate the absence of interaction between factors. Important interaction effects between H2O2-Fe (X1X2), Fe-EDTA (X2X3) and H2O2-Fe-EDTA (X1X2X3) were observed. The negative sign of the interaction effect coefficient (1.98) between H2O2 and iron means that TPHS elimination efficiency decreases with H2O2 dose increase for high level of Fe content. Although a high amount of H2O2 is a remarkable source of OH radical production, excess iron could trap and/or react with OH radicals leading to unproductive consumption of the latter and consequently inhibit TPHS oxidation. The interaction effect coefficient between iron and EDTA is also negative, and thus TPHS elimination efficiency increases with EDTA dose when total iron amount is weak. The positive sign of interaction effect coefficient between H2O2, iron and EDTA reveals that the response Y decreases with weak concentrations of these three elements. Indeed, the best removal efficiencies of soil TPHs (70.1e80.0%) were predict for H2O2/Fe/EDTA molar ratios of 20/8/1, 20/8/8, 20/1/8 and 20/1/1 in good agreement with experimental results. These latter corroborate on the one hand, the interaction influence of catalyst and chelating agent as well as of oxidant, catalyst and chelating agent. On the other hand, they evidenced that small amount of EDTA was sufficient to promote TPHs oxidation with high oxidant content (6 mol/kg dry soil) while in the absence of EDTA, an inhibitory effect was observed. By increasing H2O2 content from 4.5 to 6.0 mol/kg dry soil, the TPHs removal decreased from 29.0 to 21.0%. These results corroborated the significant effect of EDTA in the improvement of FL oxidation effectiveness at near neutral pH. Indeed, EDTA can induce and promote the extraction of bound iron (Vicente et al., 2011) and increase catalyst amount but also contaminants availability to Fenton reagents (Viisina et al., 2013) l. in the soi. In the same way, response surfaces were constructed to estimate TPHS removal efficiencies after 48 h of treatment according to significant variable and interactions. Fig. 6a, the surface plot of Y response versus H2O2 and Fe levels for EDTA content fixed at level zero, illustrated and evidenced the important interaction effect of H2O2-Fe (X1 X2). An increase in H2O2 amount and a reduction in that of iron significantly promoted FL oxidation effectiveness and consequently TPHS removal. The variations of EDTA and total iron contents for H2O2 content fixed at level zero (Fig. 6b) promoted the TPHS removal with less pronounced interaction effect of variables tested.
3.4.3. Optimization of the model and desirability The desirability function is generally used to optimize multiperformance indicators of a given process. The individual
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Table 5 Analysis of variance (ANOVA). Source of variation
Degrees of freedom
Sum of squares
Mean square
F-value
Model Residues
7 3 10
4427.3384 17.0642 4444.4025
632.477 5.688
111.1938
Y Y
90 70 50 30 10
1 -1
-1
-1
-1 1
ZVI
-1
EDTA
-0,5 0 0,5 1
0,5 1
-1 -0,5 0
-1
-0,5 0 0,5 1
-1 1
EDTA
-1 1
1
ZVI
90 70 50 30 10
H2O2
1
H2O2
90 70 50 30 10
Y
Total
Fig. 5. Interaction effects plot on TPHS degradation efficiency.
desirability function (d) values are between 0 and 1 and reflect the satisfaction degree taken by a performance indicator (response Y). The d value of 0 is assigned when the factors lead to an unacceptable response (Y < Ymin) and that of 1 when the response presents the desired maximum performance (Y > Ymax) for the considered factors, the individual desirability value (d) is determined as given in equation (6).
d¼
Y Ymin Ymax Ymin
S
^‰¤Y a ^‰¤ Ymax Ymin a
(6)
Where Ymin and Ymax are respectively the minimum and maximum values of the response and s is the factor modifying the importance of an increase in the response Y for the considered individual desirability (Colombo et al., 2013; Xie et al., 2016). The search for the optimal operating conditions leading to the optimization of TPHS elimination, from previously established model, was achieved using the response profiler (Fig. 7) whose desirability value close to 1 corresponds to maximum values of soil TPHS removal efficiencies. More the desirability function tends towards 1; the response represents a maximum performance for the considered factors. Desirability function increases significantly with H2O2 content increase. The optimal removal efficiency of TPHS after 48 h of treatment was of 79% corresponding to a maximum desirability of 0.85 and was obtained for the following conditions of 6.0, 0.3, 0.3 mol/kg dry soil of H2O2, endogenous iron and EDTA respectively corresponding to H2O2/endogenous Fe/EDTA molar ratio of 20/1/1. The optimized H2O2 dose was in good agreement with the predicted higher H2O2 levels in further works Watts et al. (2002); Goi and Trapido (2004) An increase in the amount of H2O2 promotes the increase of OH radicals and consequently the output of petroleum hydrocarbons elimination. Pardo et al. (2014) noted that the increase in H2O2 amount of simple to double improves TPHS removal efficiency in the case of polluted soil by mixture of biodiesel and diesel. Mater et al. (2007) and Villa et al. (2008) also observed an improvement of organic compounds degradation effectiveness for high concentrations in H2O2.
Fig. 6. a Surface plot of effects of H2O2 and total iron doses on TPHS removal efficiency. b Surface plot of effects of total iron and EDTA doses on TPHS removal efficiency.
H. Ouriache et al. / Chemosphere 232 (2019) 377e386
385
TPH (%)
79,25557 ±7,459526
90 70 50 30
1
-1
-1
H2O2
ZVI
EDTA
1
0,75
0,5
0,25
1 0
0,5
0
-0,5
1 -1
0,5
0
-0,5
1 -1
0,5
0
-0,5
0 0,25 0,5 0,75 1 -1
Desirability 0,851126
10
Desirability
Fig. 7. Optimum FL process factors by desirability functions for maximum TPHs removal.
4. Conclusion The pretreatment of a soil prone to an old pollution by petroleum hydrocarbons, by FL oxidation without modification of pH, was studied. The experimentations results related to the influence of H2O2 and iron showed poor yield of TPHs degradation (29.0 ÷ 39.3%), probably because of soil matrix characteristics, age of the pollution but also the weak mass transfer in solid phase reactor. The addition of a chelating agent, the EDTA improved considerably the oxidation of TPHs up to 72.2% for a ratio (H2O2/ total iron/EDTA)molar of 15/4/4 after 48 h of treatment. The use of the factorial design on two levels, has allowed the determination and the optimization of the potentially influential factors and interactions and to provide a model of prediction of the FL oxidation process in the established study domain. Endogenous iron was sufficient to catalyze H2O2 and to support TPHS oxidation up to 79.3 ± 7.5% for a molar ratio H2O2/endogenous iron/EDTA of 20/1/1. The desirability function highlighted that the maximum elimination efficiency was expected with a desirability of 0.85 under optimized condition. References Benatia, C.T., Costa, A.C.S., Tavares, C.R.G., 2009. Characterization of solids originating from the Fenton's process. J. Hazard Mater. 163, 1246e1253. Bergendhal, J.A., Thies, T.P., 2004. Fenton's oxidation of MTBE with zero-valent iron. Water Res. 38, 327e334. Catrouillet, C., Davranche, M., Dia, A., Coz, M.B.-L., Marsac, R., Pourret, O., Gruau, G., 2014. Geochemical modeling of Fe(II) binding to humic and fulvic acids. Chem. Geol. 372, 109e118. Cheng, M., Zeng, G., Huang, D., Lai, C., Xu, P., Zhang, C., Liu, Y., 2016a. Hydroxyl radicals based advanced oxidation processes (AOPs) for remediation of soils contamined with organic compound : a review. Chem. Eng. J. 284, 582e598. Cheng, M., Zeng, G., Huang, D., Lai, C., Xu, P., Zhang, C., Liu, Y., Wan, J., Gong, X., Zhu, Y., 2016b. Degradation of atrazine by a novel Fenton-like process and assessement the influence on the treated soil. J. Hazard Mater. 312, 184e191. Colombo, R., Ferreira, T.C.R., Alves, S.A., Carneiro, R.L., Lanza, M.R.V., 2013. Application of the response surface and desirability design to the Lambadacyhalothrin degradation using photo-Fenton reaction. J. Environ. Manag. 118, 32e39. Ferrarese, E., Andreottola, G., Opera, I.A., 2008. Remediation of PAH-contaminated sediments by chemical oxidation. J. Hazard Mater. 152, 128e139. Flotron, V., Delteil, C., Padellec, Y., Camel, V., 2005. Removal of sorbed polycyclic aromatic hydrocarbons from soil, sludge and sediment samples using the Fenton's reagent process. Chemosphere 59, 1427e1437. Gan, S., Yap, C.L., Ng, H.K., Venny, 2013. Investigation of the impacts of ethyl lactate based Fenton treatment on soil quality for polycyclic aromatic hydrocarbons (PAHS)-contaminated soils. J. Hazard Mater. 262, 691e700. Goi, A., Trapido, M., 2004. Degradation of polycyclic aromatic hydrocarbons in soil: the Fenton reagent versus ozonation. Environ. Technol. 25, 155e164. Goi, A., Kulik, N., Trapido, M., 2006. Combined chemical and biological treatment of
oil contaminated soil. Chemosphere 63, 1754e1763. Gray, M.R., Banerjee, D.K., Dudas, M.J., Pickard, M.A., 2000. Protocols to enhance biodegradation of hydrocarbon contaminants in soil. Ann. Finance 4, 249e257. Henz, M., Harremoes, P., La Cour Jansen, J., Arvin, E., 2002. Waste Water Treatment: Biological and Chemical Processes, third ed. Springer-Verlag, Berlin Heidelberg, Germany, p. P331. Huang, D., Hu, C., Zeng, G., Cheng, M., Xu, P., Gong, X., Wang, R., Xue, W., 2017. Combination of Fenton processes and biotreatment for wastewater treatment and soil remediation. Sci. Total Environ. 574, 1599e1610. Jia, D., Sun, S.P., Wu, Z., Wang, N., Jin, Y., Dong, W., Chen, X.D., Ke, Q., 2018. TCE degradation in groundwater by chelators-asisted Fenton-like reaction of magnetite: sand columns demonstration. J. Hazard Mater. 346, 124e132. Jorfi, S., Rezaee, A., Moheb-ali, G.A., Jaafarzadeh, N.A., 2013. Pyrene removal from contaminated soils by modified Fenton oxidation using iron nano particles. J. Environ. Sci. Health. Eng. 11, 17. Jung, Y., Park, J., Ko, S., Kim, Y., 2013. Stabilization of hydrogen peroxide using phthalic acids in the Fenton and Fenton-like oxidation. Chemosphere 90, 812e819. Kulik, N., Goi, A., Trapido, M., Tuhkanen, T., 2006. Degradation of polycyclic aromatic hydrocarbons by combined chemical pre-oxidation and bioremediation in creosote contaminated soil. J. Environ. Manag. 78, 382e391. Kwan, W.P., Volker, B.M., 2003. Rates of hydroxyl radical generation and organic compound oxidation in mineral-catalyzed Fenton-like systems. Environ. Sci. Technol. 37, 1150e1158. Lu, M., Zhang, Z., Qiao, W., Guan, Y., Xiao, M., Peng, C., 2010a. Removal of residual contaminants in petroleum-contaminated soil by Fenton-like oxidation. J. Hazard Mater. 179, 604e611. Lu, M., Zhang, Z., Qiao, W., Wei, X., Guan, Y., Maa, Q., Guan, Y., 2010b. Remediation of petroleum-contaminated soil after composting by sequential treatment with Fenton-like oxidation and biodegradation. Bioresour. Technol. 101, 2106e2113. Mater, L., Rosa, E.V.C., Berto, J., Correa, A.X.R., Schwingel, P.R., Radetski, C.M., 2007. A simple methodology to evaluate influence of H2O2 and Fe2þ concentrations on the mineralization and biodegradability of organic compounds in water and soil contaminated with Crude petroleum. J. Hazard Mater. 149, 379e386. thodes choisies. Mathieu, C., Pieltain, F., 2003. In: Analyse chimique des sols e Me Tec et Doc - Lavoisier, Paris, p. 388p. Matta, R., Hanna, K., Chiron, S., 2007. Fenton-like oxidation of 2,4,6-trinitotoluene using different iron minerals. Sci. Total Environ. 385, 242e251. Mc Grath, S.P., Cunliffe, C.H., 1985. A simplified method for the extraction of the metals Fe, Zn, Cu, Ni, Cd, Pb, Cr, Co and Mn from soils and sewage sludges. J. Sci. Food Agric. 36 (9), 794e798. Nam, K., Rodriguez, W., Kukor, J.J., 2001. Enhanced degradation of polycyclic aromatic hydrocarbons by biodegradation combined with a modified Fenton reaction. Chemosphere 45, 11e20. Pardo, F., Rosas, J.M., Santos, A., Ramero, A., 2014. Remediation of a biodiesel blendcontaminated soil by using a modified Fenton process. Environ. Sci. Pollut. Res. 21, 198e207. Quan, H.N., Teel, A.L., Watts, R.J., 2003. Effect of contaminant hydrophobicity on hydrogen peroxide dosage requirements in the Fenton-like treatment of soils. J. Hazard Mater. 102, 277e289. Romero, A., Santos, A., Cordero, T., Rodriguez-Mirasol, J., Rosas, J.M., Vicente, F., 2011. Soil remediation by Fenton-like process : phenol removal and soil organic matter modification. Chem. Eng. J. 170, 36e43. Seibig, S., Van Eldik, R., 1997. Kinetics of [FeII(edta)] oxidation by molecular oxygen revisited. New evidence for a multistep mechanism. Inorg. Chem. 36 (18), 4115e4120. Sherwood, M.K., Cassidy, D.P., 2014. Modified Fenton oxidation of diesel fuel in arctic soils rich in organic matter and iron. Chemosphere 113, 56e61.
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Silva-Castro, G.A., Rodelas, B., Perucha, C., Laguna, J., 2013. Bioremediation of dieselpolluted soil using biostimulation as post-treatment after oxidation with Fenton-like reagents: assays in a pilot plant. Sci. Total Environ. 445e446, 347e355. Sirguey, C., Silva, P.T.S., Schwartz, C., Simonnot, M.O., 2008. Impact of chemical oxidation on soil quality. Chemosphere 72, 282e289. Sun, H., Yan, Q., 2008. Influence of pyrene combination state in soils on its treatment efficiency by Fenton oxidation. J. Environ. Manag. 88, 556e563. Usman, M., Faure, P., Ruby, C., Hanna, K., 2012a. Remediation of PAH-contaminated soils by magnetite catalyzed Fenton-like oxidation. Appl. Catal., B 117e118, 10e17. Usman, M., Faure, P., Hanna, K., Abdelmoula, M., Ruby, C., 2012b. Application of magnetite catalyzed chemical oxidation (Fenton-like and persulfate) for the remediation of oil hydrocarbon contamination. Fuel 96, 270e276. Valderrama, C., Alessandri, R., Aunola, T., Cortina, J.L., Gamisans, X., Tuhkanen, T., 2009. Oxidation by Fenton's reagent combined with biological treatment applied to a creosote-comtaminated soil. J. Hazard Mater. 166, 594e602. Venny, Gan, S., Ng, H.K., 2012. Modified Fenton oxidation of polycyclic aromatic hydrocarbon (PAH)-contaminated soils and the potential of bioremediation as post-treatment. Sci. Total Environ. 419, 240e249. Vicente, F., Rosas, J.M., Santos, A., Romero, A., 2011. Improvement soil remediation by using stabilizers and chelating agents in a Fenton-like process. Chem. Eng. J. 172, 689e697. Viisina, M., Karpenko, O., Novikov, V., Trapido, M., Goi, A., 2013. Influence of biosurfactant on combined chemicalebiological treatment of PCB-contaminated
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Treatment of petroleum hydrocarbons contaminated soil by Fenton like oxidation H. Ouriache a, J. Arrar a, *, A. Namane a, F. Bentahar b a Laboratoire des Sciences et Techniques de l’Environnement (LSTE), Ecole Nationale Polytechnique, Avenue Hassen Badi, BP 182 El Harrach, 16110, Algiers, Algeria b Laboratoire des Ph enom enes de Transfert, Facult e de G enie M ecanique et G enie des Proc ed es, Universit e des Sciences et de la Technologie Houari Boumediene, BP 32 El Alia Bab Ezzaouar, 16111, Algiers, Algeria
h i g h l i g h t s FL oxidation without pH modification for aged petroleum hydrocarbons contaminated soil. Parametric study and Statistically designed experiment on FL oxidation performances. H202, key factor affecting TPHS removal efficiency with important interaction effects H2O2-Fe, Fe-EDTA and H2O2-Fe-EDTA. Endogenous iron exhibits high catalytic potential to activate H2O2 in presence of EDTA.
a r t i c l e i n f o
a b s t r a c t
Article history: Received 30 January 2019 Received in revised form 5 May 2019 Accepted 7 May 2019 Available online 10 May 2019
Experimental tests were carried out in solid phase reactors on a microcosm scale, to removal old petroleum pollution by Fenton like oxidation process. In order to optimize the process, parametric study and statistically designed experiment have been undertaken by considering the amount influence of hydrogen peroxide (H2O2), endogenous and zero-valent iron (Fe) and ethylene diamine tetraacetic acid (EDTA) as chelating agent. The measurement of residual total petroleum hydrocarbons for different H2O2/Fe molar ratios and pH in the vicinity of neutrality highlighted oxidation rates ranging between 29.0 and 39.3%. The Fenton like (FL) oxidation was optimal for H2O2/Fe molar ratio of 15/4. The use EDTA led to result up 72.2% for H2O2/ total Fe/EDTA molar ratio of 15/4/4 after 48 h of treatment. The statistical analysis of data by factorial design, has allowed the modeling of Fenton like process performances in the operating domain. It showed that hydrogen peroxide amount, interaction effects of oxidant-catalyst, catalyst-chelating agent, and oxidant-catalyst-chelating agent, were the influential parameters. Moreover, these results suggest that endogenous iron could be used as a source of iron in the presence of the chelating agent to activate FL oxidation. A better accuracy (80.0%) was obtained by statistical analysis for H2O2/endogenous Fe/EDTA molar ratio of 20/1/1. © 2019 Elsevier Ltd. All rights reserved.
Handling Editor: X. Cao Keywords: Fenton-like Soil remediation Petroleum hydrocarbons EDTA Oxidation
1. Introduction The pollution of soils in Algeria constitutes major problem in view of the number of contaminated sites for years even decade, potential hazards that threaten environment and human health and the need to treat and/or restore them. Petroleum oils and their derivatives, resulting from oil industry activities, accidental discharges, leakages from underground storage tanks and ruptures of
* Corresponding author. E-mail address: [email protected] (J. Arrar). https://doi.org/10.1016/j.chemosphere.2019.05.060 0045-6535/© 2019 Elsevier Ltd. All rights reserved.
pipelines, are the main source of pollution. 1.1. Different treatment techniques can be applied … Bioremediation is considered as an environmental and economic approach for the treatment However, the presence of recalcitrant and/or toxic substances (Kulik et al., 2006), the constraints of deadlines (Kulik et al., 2006) and residual levels of pollutants (Usman et al., 2012b) require fast and effective treatments such as combining chemical oxidation with bioremediation. Indeed, advanced oxidation processes are a good alternative for
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the remediation of soils subject to old contamination with toxic and persistent organic pollutants (Cheng et al., 2016a; Huang et al., 2017) and have the advantages to be rapid and relatively efficient (Goi et al., 2006; Ferrarese et al., 2008). These processes can be used until disappearance of toxicity and/or generation of more biodegradable and/or harmless by-products (Kulik et al., 2006; Mater et al., 2007; Silva-Castro et al., 2013; Valderrama et al., 2009; Venny et al., 2012). Among these processes, Fenton treatments are ones of the best options (Yap et al., 2011), because of their high potential to treat contaminated soils their simplicity to be implemented (Ferrarese et al., 2008; Venny et al., 2012). They use the high reactivity of the hydroxyl radical (OH ) generated by the Fenton reaction and able to oxidize almost all organic contaminant types (Cheng et al. 2016b; Gan et al., 2013; Lu et al., 2010b). However, Its application is limited by the optimum pH very acidic (3) to inhibit iron precipitation (Sirguey et al., 2008) and its negative impacts on soil fate. In addition, Zhou et al. (2009) showed that continuous iron addition was necessary to achieve complete degradation of target contaminants. To overcome these drawback, Fenton like (FL) oxidation has been developed using catalysts such as, mineral iron oxides (ferrihydrite (Fe2(OH)6), hematite (Fe2O3) or goethite (a-FeOOH)) (Ferrarese et al., 2008) or zero-valent iron, for an effective degradation of organic contaminants in the range of neutral pH (Usman et al., 2012b). Matta et al. (2007) and Xue et al. (2009) noticed that mineral oxides of Fe(II), such as magnetite (mixture of Fe(II) and Fe(III), are more effective catalyst compared to mineral Fe(III) oxides such as hematite, goethite and ferrihydrite. The application of magnetite as a catalyst to activate hydrogen peroxide resulted in crude oil removal efficiencies of up to 80%, while soluble Fe2þ species generated weak efficiencies of 10e15% (Usman et al., 2012b). The addition of chelating agents, such as catechol, gallic acid, oxalic acid, ethylene diamine tetracetic acid, is generally recommended to enhance the FL treatment efficiency and to prevent iron precipitation at natural soil pH (Xu et al., 2011; Venny et al., 2012 Romero et al., 2011). According to Seibig and Van Eldik (1997) and Viisimaa et al. (2013), chelating agents promote the formation of hydroxyl radicals or other oxidants and the production of dioxygene and possibly hydrogen peroxide.). This work deals with the soil removal of petroleum hydrocarbons in the case of an old pollution by FL oxidation without pH modification and the determination of the optimal conditions. The effects of hydrogen peroxide (H2O2), endogenous and zero valent iron (Fe), and ethylene diamine tetracetic acid (EDTA) are studied. The application of an experimental design was used to assess and optimize the potentially influential parameters on the removal of petroleum hydrocarbons soil and the modeling of FL process in the case of the studied soil.
2. Material and methods 2.1. Reagents All chemical reagents and solvents used were of analytical grade and used as received without purification. Deionized water (GFL inmbH D-30938 Burgwedel, 2008) was used for all prepared solutions. The powder of iron was purchased from Chemopharma with purity of 98.5%. It was characterized as micro-valent iron with an average of particle size of 37 mm (Mastersizer2000, Malvern Instruments) and Brunauer-Emmet Teller (BET) surface area of 6.78 ± 0.03 m2/g (Micrometrics ASAP, 2010V5.02H).
2.2. Soil Studied soil was sampled from a polluted site by petroleum hydrocarbons since the 1990s and located at 36 11026, 01 North, 3 11008, 0 East in Dar El Beida, the east of Algiers. The soil samples were collected, according to standard method, up to 20 cm a depth; air dried at room temperature, sieved at 0.8 mm, and homogenized according to the quartering method (twice redone). The pretreated soil was then stored at 4 C in the dark until use. 2.3. Soil characterization The main physic-chemical parameters of soil were analyzed according to standard methods. Particle size distribution was determined by sieving and sedimentation after destruction of the organic matter with hydrogen peroxide and dispersion with sodium hexametaphosphate (Mathieu and Pieltain, 2003). The soil pH was determined using pH meter (Hanna) with a soil deionized water ratio of 1/5 w/v after 1 h stirring. The moisture content was determined by drying at 105 C up to constant weight. Organic matter and organic carbon were determined respectively by calcinations at 550 C for 4 h and by digestion with potassium dichromate in acidic media and titration according to Anne's method (Mathieu and Pieltain, 2003). Total iron was determined by flame atomic absorption spectrophotometer (Agilent 240 Z AA) after calcination followed by aqua regal (4:1 v/v concentrated hydrochloric acid to concentrated nitric acid) digestion according to Mc Grath and Cunliffe (1985). All measures of the above parameters were done in triplicate and the average of the three independent measures was reported. Quantification of oil pollution levels was performed from the determination of total petroleum hydrocarbons (TPHs) by the gravimetric method. 1 g of contaminated soil sample was mixed and crushed with anhydrous sodium sulfate according to a mass ratio of 4/5 and extracted with dichloromethane (DCM) by sonication for 15 min. After centrifugation, the extract was removed and the process repeated twice, the first with 12 mL and the second with 6 mL of DCM; total extract was concentrated at 40 C (rotary evaporation) and then weighed. The TPHs content was revised to dry weight. The variation of the reproducibility of TPHs measure was determined by duplicating sampling and the average result was reported. 2.4. Soil microcosm experiments Experiment essays were carried out on a microcosm scale in solid phase reactor at lightless and ambient temperature during 48 h. 150 g of contaminated soil samples to be treated were introduced in 250 ml Erlenmeyer and placed on an orbital vibrating shaker at 150rd/min. These samples were previously sterilized with 0.2% mercury chloride (Nam et al. 2001) and sprinkled with deionized water to ensure a moisture content of 25%. Removal of soil TPHs was carried out by FL oxidation without adjustment of pH, the hydrogen peroxide being catalyzed by endogenous iron and by both endogenous and micro zero valent iron. In a first part, each reactor received different quantities of hydrogen peroxide according to H2O2/Fe molar ratios ranging from 1/1 to 20/1 to reveal hydrogen peroxide influence on TPHs removal. In a second part, each reactor received the same amount of hydrogen peroxide, the content being fixed at 4.5 mol H2O2/kg of dry soil, and different quantities of iron powder according to various molar ratios of H2O2/Fe going from 15/1 to 15/8 in reference to both endogenous and exogenous iron. A third series of experiments focused on the influence of ethylene diamine tetraacetic acid
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addition according to different H2O2/Fe/EDTA molars ratios by considering optimal quantities of hydrogen peroxide and total iron. For all the experiments, FL oxidation was initiated with the introduction of H2O2 and its mixing with soil and all other additives. The TPHs content, the pH and the moisture content were periodically monitored for 48 h. The latter was maintained between 25 and 30%. The oxidation reaction was stopped by addition of sodium sulphite (Valderrama et al., 2009) to monitor the residual TPHs from the treated soil. 2.5. Process optimization analysis Factorial experiment design was used to determine main effects of H2O2, total iron and EDTA contents, as well as interaction effects between them to optimize and predict Fenton-like process. The experiments were arranged according to a factorial design with three factors on two distinct levels (23). Table 1, presents the limits of variation of the independent variables. The low, centre and high levels of each independent factor were designed as 1, 0, þ1 level respectively. 3. Results and discussion
379
and Cassidy, 2014).
Fe0 þ H2 O2 /Fe2þ þ 2OH Fe2þ þ H2 02 /Fe3þ þ OH þ HO
(1a)
(1b)
This increase was less significant with iron addition. Beyond 1.2 mol/kg dry soil of iron (H2O2/Fe ¼ 15/4), the recorded values of pH were lower (˂7) than the natural pH (Fig. 1b). This diminution could be associated to hydrogen peroxide stabilization (Jung et al., 2013; Vicente et al., 2011). In the case of EDTA (Fig. 1c), the increase in pH was moderate, probably due to the generation of hydrogen peroxide in the medium and hydroxide ions resulting from the reaction of EDTA with iron (Zhou et al., 2009). Sherwood and Cassidy (2014) recorded similar values of pH regardless of the presence of EDTA. Goi et al. (2006); Usman et al. (2012a) and Sherwood and Cassidy (2014) did not observe soil pH changes during FL oxidation pretreatment while Vicente et al. (2011) observed a decrease in soil pH (˂7) initially ranging between 7 and 8.2. Soil acidification would be mainly allotted to a modification of the surface charge or the redox potential of mineral surface by the precipitation of cations (Vicente et al., 2011).
3.1. Soil characteristics 3.3. And total iron/EDTA (1c) The main results of the soil characterization are reported in Table 2. The soil particle size analysis (Table 2) revealed a loam texture with 15% of clay, 35.75% of silt and 49.25% of sand. Permeability measurement highlighted a permeable soil in favor of best transfer between the different phase and good oxygenation. Soil pH was in the range for the development of microbial population and the growth of hydrocarbons degrader microorganisms (Gray et al., 2000) in the event of biological treatment. Organic matter and TPHs contents were respectively of 6.0% and 3.0%. The total iron content of 16.8 g/kg is significant regarding to Fenton oxidation. 3.2. Fenton-like oxidation treatment 3.2.1. pH Addition of FL reagents and EDTA affected little the initial pH (Fig. 1). In general, FL reaction was accompanied by increases in pH in a field of 7.2e7.9. The increase in pH with hydrogen peroxide addition (Fig. 1a) could be allotted to the hydroxide ion release according to reactions.(1) (Bergendhal and Thies, 2004; Sherwood
Table 1 Factors and coded levels for the experiment design. Independent Variables (mol./kg dried soil)
Factors
H2O2 Iron EDTA
X1 X2 X3
Coded level 1
0
þ1
0.30 0.30 0.30
3.15 1.35 1.35
6.00 2.40 2.40
3.3.1. Total petroleum hydrocarbons FL treatment efficiency depends on soil matrix (Kulik et al., 2006; Sun and Yan, 2008), and age and extent contamination, and consequently requires the determination of optimum conditions for efficient application. Hydrogen peroxide (H2O2) influence on TPHs removal without iron addition was studied for different contents ranging from 0.3 to 6.0 mol H2O2/kg dry soil. The results of residual TPHs (Fig. 2a) highlighted the catalytic potential of endogenous iron with oxidation yields of soil petroleum hydrocarbons between 7.3 and 29.0% after 48 h of treatment. Indeed, several studies showed that iron minerals naturally present in soil exhibit different catalytic activities depending on the surface charge of iron or its oxidation state under pH conditions ranging from 4 to 9 (Kwan and Volker, 2003). Yeh et al. (2003) reported 78% of sorbed TCE reduction by 3% of H2O2 in the case of aquiferous sand containing 2.01 g of extractable iron/kg sand. Soil TPHs removal increased with H2O2 amount up to 29%, for then decrease beyond an H2O2 content of 4.5 mol/kg dry soil. Similar tendencies were reported in the literature (Flotron et al., 2005; Goi et al., 2006; Watts et al., 2002). Excess of H2O2 reduced TPHs oxidation effectiveness and inhibited FL process for H2O2/Fe molar ratio of 20/1. This inhibition could be the result of a significant consumption and/or scavenging of OH radicals by H2O2 excess (Yap et al., 2011) and the formation of less reactive HO2 radicals as presented by reactions (2) and (3) (Watts et al., 2002).
HO þ H2 O2 /H2 O þ HO2
(2)
HO þ HO2 /H2 O þ 02
Table 2 Soil chemical characteristics. pH
7.21 ± 0.11
Texture
Loam
Humidity (%) Organic Matter (%) Organic Carbon (%) BET Surface Area (m2.g-1) TPHs (g.kg-1) Total Iron (Fe) (%)
2.46 ± 0.06 5.97 ± 0.16 2.08 ± 0.01 24.42 ± 0.12 30.51 ± 0.46 1.68 ± 0.10
Clay (%) Loam (%) Sand (%) d60 (mm) Cu (D60/D10) Permeability (m.s-1)
15.00 ± 0.11 35.75 ± 0.25 49.25 ± 0.50 160 10.66 5.56 10-5
(3)
Furthermore, too high doses of H2O2 generate the decomposition of the latter and limit the production of OH radicals and other
radical or non-radical species such as HO2 ; O2 and HO 2 , (Xu et al., 2011). According to Walling (1975), an excess of H2O2 could compete with organic substances with respect to OH radicals, thus reducing their efficiency and the oxidation of pollutants. The optimal amount of H2O2 for an effective oxidation varies
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Fig. 1. pH variations according to the H2O2 dose (1a), total iron dose (1b).
according to organic compounds reactivity with respect OH radical. Many studies refer to an optimal molar ratio H2O2/Fe of 10/1 between hydrogen peroxide and iron (Goi and Trapido, 2004; Kulik et al., 2006; Sun and Yan, 2008; Valderrama et al., 2009; Usman et al., 2012a). The maximum removal rate of TPHS of 29% was
obtained for H2O2/Fe molar ratio of 15/1 corresponding to H2O2 content of 4.5 mol/kg dry soil. This result was in good agreement with those of further related studies which provide optimal values of H2O2/Fe molar ratios between 5/1e25/1 (Jorfi et al., 2013). Valderrama et al. (2009) recorded a diminution in total PAHS removal rate of 80% when H2O2/Fe2þ molar ratio increases from 10/ 1 to 40/1. Xu et al. (2011) observed a maximum elimination of TPHS of 23% and 24% for 42/1 and 210/1 M ratios respectively. Lu et al. (2010b) obtained a maximum removal efficiency of total dichloromethane-extractable organics with H2O2/Fe3þ molar ratio of 300/1, the H2O2 dose being fixed at 0.49 mol/kg dry soil. Usman et al. (2012b) reported that the application of magnetite as a catalyst to activate hydrogen peroxide provided high efficiency (80%) of crude oil contaminated soil remediation for H2O2/Fe molar ratio of 10/1. Under optimized conditions, Watts et al. (2002) achieved 85% of benzo[a]pyrene mineralization using 15 M H2O2 catalyzed by endogenous iron and reported for FL treatment, that the optimized H2O2 contents were normally higher than 5 M. Goi and Trapido (2004) reported that oxidation of PAHscontaminated soil with high H2O2 contents was effective even for aged polluted soil and resulted in efficiencies between 40 and 86%. Finally, highly hydrophobic compounds generally require high H2O2 doses while less soluble compounds can be degraded with relatively weak doses (Villa et al., 2008). Although Yap et al. (2011) reported that FL reaction with iron oxides gives high degradation efficiency at near neutral pH between 7.0 and 8.0 and that the oxidation of sorbed contaminants was possible with high doses of H2O2 (Watts et al., 2002; Quan et al., 2003), the TPHs oxidation efficiency in our case did not exceed 29%. In view of relatively weak efficiencies (29%) obtained with endogenous iron, the TPHs removal from the studied soil requires more significant amounts of iron to be determined. For that purpose, the zero valent iron (ZVI) powder was used and H2O2 content of 4.5 mol/kg dry soil was considered as the optimum value for the further essays. In general, the increase in iron content improved the oxidation rate of organic pollutants due to the increase in the number of active sites to catalyze H2O2 and the production of more OH radicals (Yap et al., 2011). The addition of iron (Fig. 2b) generated a light increase in TPHs removal efficiency to reach a maximum of 39.3 ± 3.8% for H2O2/Fe molar ratio of 15/4, by considering total iron, for then decrease. It should be noted that for H2O2/Fe molar ratios greater than 15/ 4, red deposits, probably iron hydroxides, were observed and could be responsible for the inhibition of FL oxidation. Benatia et al. (2009) and Henz et al. (2002) observed the same phenomenon with iron based catalyst for pH > 5. Furthermore, excess of iron also causes unproductive consumption of hydroxyl radicals (Lu et al., 2010a) and undesirable side reactions which increase the scavenging of OH radicals (Yap et al., 2011). The addition of iron improved TPHs removal efficiency by only 37.4% compared with endogenous iron alone. This improvement, not significant, could be allotted to performances of micro-zerovalent iron (mZVI) used. It could also be awarded to the sorption of Fe species on organic compounds in the soil, which was more significant as the pH gets higher (Catrouillet et al., 2014). This makes iron species less available for the Fenton reaction activation. In addition, pollution aging and organic matter are all factors that can limit the availability of contaminants to Fenton's reagents, and promote the sequestration of OH radicals as shown by previous work of Sun and Yan (2008). In order to improve performances of FL oxidation process and to promote hydroxyl radicals formation or other oxidants and
H. Ouriache et al. / Chemosphere 232 (2019) 377e386
381
40 [Fe]=0.3mol/kg dry soil 35
0H
24H
48H
TPHs (g/kg dry soil)
30 25 20 15 10 5 0 01:01
05:01
10:01
11:01 12:01 13:01 (H 2O2/Fe)molar ratio
14:01
15:01
20:01
40 [H 2O2]=4.5mol/kg dry soil 35
0H
24H
48H
TPHs (g/kg drY soil)
30 25 20 15 10 5 0 15:01
15:02
15:03 15:04 (H 2O2/Fe)molar ratio
15:06
15:08
Fig. 2. a Temporal TPHs evolution according to H2O2 level variations. b: Temporal TPHs evolution according to iron level variations. c: Temporal TPHs evolution according to EDTA level variations.
consequently the TPHs soil removal, we have used ethylene diamine tetraacetic acid (EDTA) according to different H2O2/Fe/ EDTA molar ratios. Results (Fig. 2c) showed that EDTA led to significant increase in TPHs removal, independently of iron addition and thus, the performance of FL oxidation. EDTA addition contributed to an increase of 80.8% (without Fe addition) and 83.6% (with Fe addition) for respective H2O2/Fe/EDTA molar ratios of 15/1/4 and 15/4/4 in comparison with these last ones of 15/1/0 and 15/4/0. The highest TPHs removal efficiencies of 72.2% were observed for H2O2/ Fe/EDTA molar ratios of 15/4/4 and 15/4/8 and highlight an optimal Fe/EDTA molar ratio of 1/1 to be implemented. This last ratio corroborates the results of further works in the field of soil remediation by FL oxidation and is especially recommended for hydrophobic organic contaminants (Xue et al., 2009; Lu et al., 2010a).
The increase in soil TPHs removal efficiency with EDTA addition could be awarded to changes in the surface charge or the oxidation state of iron leading to an improvement of catalytic potential of this last and/or to iron complexes formation in favor of catalyst availability (Vicente et al., 2011). This increase could also result from the generation of H2O2 in the medium according to Zhou et al. (2009) and/or a reduction of its assimilation. Indeed, EDTA greatly decreased H2O2 uptake, probably due to the competition between chelating agent and H2O2 for surface sites on endogenous iron according to Jia et al. (2018). Decrease in H2O2 decomposition rates was also observed with EDTA use at neutral pH (Xue et al., 2009). Jia et al. (2018) reported that addition of EDTA enhanced TCE degradation in sand columns with high content of magnetite (7.0%) and inhibited it with small content of magnetite (0.5%). Lu et al. (2010a) obtained the best results of 38.3% for H2O2/Fe3þ molar
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40 [H 2O2]/[Fe]/[EDTA]
35
15/4/00
15/4/04
24 Times (hours)
27
15/4/08
15/1/04
TPHs (g/kg dry soil)
30 25 20 15 10 5 0 0
3
48
Fig. 2. (continued).
3.4. Factorial design The experimental tests were organized and carried out according to an experiment matrix, written in coded variables as shown in Table 3 to model the TPHS removal (response Y) in the previously established study domain. For a statistical significance evaluation of the effects and interactions, 3 centre points were carried out. TPHS removal efficiencies by FL oxidation, were adjusted with a polynomial model of the 1st order connecting the response Y to variables Xi¼1,2,3 given by equation (4). The model coefficients were determined using JMP 8.0 statistical analysis software.
Table 3 Experimental results of 23 full factorial design. Experimental number
Point type
X1
X2
X3
Response Y(%)
01 02 03 04 05 06 07 08 09 10 11
Factorial Factorial Factorial Factorial Factoria Factorial Factorial Factorial Centre Centre Centre
1 þ1 1 þ1 1 þ1 1 þ1 0 0 0
1 1 þ1 þ1 1 1 þ1 þ1 0 0 0
1 1 1 1 þ1 þ1 þ1 þ1 0 0 0
18.80 80.01 35.10 70.10 36.10 79.21 31.76 75.11 50.98 50.13 50.45
Y ¼ 51:62 þ 24:10X1 1:49X2 þ 1:01X3 1:98X1 X2 þ 0:02X1 X3 3:12X2 X3 þ 4:54X1 X2 X3 (4) Where variables Xi¼1,2,3 are the coded values of the contents of hydrogen peroxide (H2O2) (3.15 þ 2.85X1 (mole/kg dry soil)), total iron (Fe) (1.35 þ 1.05X2 (mole/kg dry soil)) and ethylene diamine tetraacetic acid (EDTA) (1.35 þ 1.05X3 (mole/kg dry soil)) respectively. 3.4.1. Regression models and statistical testing The plot of experimental versus predicted responses (Fig. 3) showed square correlation coefficients R2 and adjusted R2 respectively equal to 0.999 and 0.996. Only 0.4% of the total variance could not be explained by the used model. The high values of these two coefficients and their
90 80
Experimental Response
ratio of 200/1, a slurry pH of 7, the H2O2 dose and EDTA/Fe molar ratio being fixed at 0.49 mol/kg dry soil and 1/1 respectively. Viisimaa et al. (2013) highlighted that EDTA addition not only chelates and mobilizes the metals from soil but also substantially increases the soil contaminant availability, thus improving contaminants oxidation. The microcosmal scale (unsaturated soil) test results revealed, in addition to the effectiveness and the feasibility of the FL oxidation process in the case of an old soil pollution, that Fenton reagents and EDTA influence the oxidation effectiveness of soil TPHS with synergistic and antagonistic effects in the study domain from where the relevance to optimize the process.
70 60 50 40 30 20 10 10
20
30
40 50 60 Estimated Response R2=0.9961
70
80
Fig. 3. Comparison of the estimated and experimental response.
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significant concordance ensure a very good descriptive quality of the model. The regression coefficients significance in equation (4) was verified by the Student t-test application. An effect will be considered if the associated absolute t-value is greater than t-critic equal to 3.182 (Student table) for 95% confidence level. Another method is to consider the probability value (p-value) of each model term closer to zero and which must be less than or equal to the threshold p of 0.05. These tests, from the review of tvalues and p-values (Table 4) highlighted 3 non significant coefficients (a2, a3 and a13) for Y response. These results were also confirmed by the Pareto Chart test (Fig. 4), which shows each effects and interactions estimated by decreasing order of importance, where the vertical line defines 95% of the confidence interval. It arises from the different significance tests, that only the variable X1 and the interactions X1X2, X2X3, and X1X2X3 affect significantly the soil TPHS removal efficiency (response Y). As a result, the model was adjusted by considering only the influential linear and interaction effects (equation (5)).
Y ¼ 51:62 þ 24:1OX1 1:98X1 X2 3:12X2 X3 þ 4:54X1 X2 X3 (5) To check the significance of the model variables retained, a Fisher test was established. Analysis of variance (ANOVA) showed a fairly high mean square of regression compared to the main square of residues (Table 5) and consequently a Fisher value (F ¼ 111.19) mush higher than the critical one (F0.05; 7; 3 ¼ 8.89). This means a good adequacy of model regression to experimental data at a 95% confidence level. 3.4.2. Average effects of the factors and interactions Analysis of the adjusted model given in equation (5) indicated that the amount of H2O2 (X1) is the key factor affecting the soil TPHS removal efficiency (response Y) since its coefficient is the higher modulus. In addition, its positive sign means that TPHs removal efficiency increases significantly with H2O2 content. These results corroborate the experimental results obtained in the first stage while varying H2O2 dose only. Conversely, iron content (X2) was found statistically insignificant for the response Y probably due to the capacity of endogenous iron (0.3 mol/kg dry soil) to catalyze H2O2 and to generate maximum removal of soil TPHs for H2O2 content of 6.0 mol/kg dry soil. These results corroborate works of Kwan and Volker (2003), Goi et al. (2006), Kulik et al. (2006), Xue et al. (2009), Yap et al. (2011), Jung et al. (2013), which evidenced that iron oxides naturally present in soil can catalyze H2O2 and promote organic contaminants oxidation under pH in the field of neutrality. Effects of iron (X2) and EDTA (X3) contents were not directly influential but were through interactions effects at the 95% confidence level as shown in Fig. 5. The plots of interaction effects
Table 4 The model coefficients analysis of the Y response. Coefficients a0 a1 a2 a3 a a a a a
12 13 23 123
values 51.622 24.096 1.493 1.008 1.983 0.018 3.116 4.543
Standard deviation 0.403944 0.473666 0.473666 0.473666 0.473666 0.473666 0.473666 0.473666
Values which respond to significant tests.
t-value a
127.80 50.87a 3.15 2.13 4.19a 0.04 6.58a 9.59a
p-value <0.0001a <0.0001a 0.0511 0.1231 0.0248a 0.9709 0.0071a 0.00241a
383
Terms H2O2 H2O2*ZVI*EDTA H2O2*ZVI EDTA ZVI*EDTA H2O2*EDTA ZVI Fig. 4. Pareto Chart for standardized effects.
evidenced interaction existence between two factors, when the two lines of levels 1 and þ1 are not parallel. The parallel lines indicate the absence of interaction between factors. Important interaction effects between H2O2-Fe (X1X2), Fe-EDTA (X2X3) and H2O2-Fe-EDTA (X1X2X3) were observed. The negative sign of the interaction effect coefficient (1.98) between H2O2 and iron means that TPHS elimination efficiency decreases with H2O2 dose increase for high level of Fe content. Although a high amount of H2O2 is a remarkable source of OH radical production, excess iron could trap and/or react with OH radicals leading to unproductive consumption of the latter and consequently inhibit TPHS oxidation. The interaction effect coefficient between iron and EDTA is also negative, and thus TPHS elimination efficiency increases with EDTA dose when total iron amount is weak. The positive sign of interaction effect coefficient between H2O2, iron and EDTA reveals that the response Y decreases with weak concentrations of these three elements. Indeed, the best removal efficiencies of soil TPHs (70.1e80.0%) were predict for H2O2/Fe/EDTA molar ratios of 20/8/1, 20/8/8, 20/1/8 and 20/1/1 in good agreement with experimental results. These latter corroborate on the one hand, the interaction influence of catalyst and chelating agent as well as of oxidant, catalyst and chelating agent. On the other hand, they evidenced that small amount of EDTA was sufficient to promote TPHs oxidation with high oxidant content (6 mol/kg dry soil) while in the absence of EDTA, an inhibitory effect was observed. By increasing H2O2 content from 4.5 to 6.0 mol/kg dry soil, the TPHs removal decreased from 29.0 to 21.0%. These results corroborated the significant effect of EDTA in the improvement of FL oxidation effectiveness at near neutral pH. Indeed, EDTA can induce and promote the extraction of bound iron (Vicente et al., 2011) and increase catalyst amount but also contaminants availability to Fenton reagents (Viisina et al., 2013) l. in the soi. In the same way, response surfaces were constructed to estimate TPHS removal efficiencies after 48 h of treatment according to significant variable and interactions. Fig. 6a, the surface plot of Y response versus H2O2 and Fe levels for EDTA content fixed at level zero, illustrated and evidenced the important interaction effect of H2O2-Fe (X1 X2). An increase in H2O2 amount and a reduction in that of iron significantly promoted FL oxidation effectiveness and consequently TPHS removal. The variations of EDTA and total iron contents for H2O2 content fixed at level zero (Fig. 6b) promoted the TPHS removal with less pronounced interaction effect of variables tested.
3.4.3. Optimization of the model and desirability The desirability function is generally used to optimize multiperformance indicators of a given process. The individual
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Table 5 Analysis of variance (ANOVA). Source of variation
Degrees of freedom
Sum of squares
Mean square
F-value
Model Residues
7 3 10
4427.3384 17.0642 4444.4025
632.477 5.688
111.1938
Y Y
90 70 50 30 10
1 -1
-1
-1
-1 1
ZVI
-1
EDTA
-0,5 0 0,5 1
0,5 1
-1 -0,5 0
-1
-0,5 0 0,5 1
-1 1
EDTA
-1 1
1
ZVI
90 70 50 30 10
H2O2
1
H2O2
90 70 50 30 10
Y
Total
Fig. 5. Interaction effects plot on TPHS degradation efficiency.
desirability function (d) values are between 0 and 1 and reflect the satisfaction degree taken by a performance indicator (response Y). The d value of 0 is assigned when the factors lead to an unacceptable response (Y < Ymin) and that of 1 when the response presents the desired maximum performance (Y > Ymax) for the considered factors, the individual desirability value (d) is determined as given in equation (6).
d¼
Y Ymin Ymax Ymin
S
^‰¤Y a ^‰¤ Ymax Ymin a
(6)
Where Ymin and Ymax are respectively the minimum and maximum values of the response and s is the factor modifying the importance of an increase in the response Y for the considered individual desirability (Colombo et al., 2013; Xie et al., 2016). The search for the optimal operating conditions leading to the optimization of TPHS elimination, from previously established model, was achieved using the response profiler (Fig. 7) whose desirability value close to 1 corresponds to maximum values of soil TPHS removal efficiencies. More the desirability function tends towards 1; the response represents a maximum performance for the considered factors. Desirability function increases significantly with H2O2 content increase. The optimal removal efficiency of TPHS after 48 h of treatment was of 79% corresponding to a maximum desirability of 0.85 and was obtained for the following conditions of 6.0, 0.3, 0.3 mol/kg dry soil of H2O2, endogenous iron and EDTA respectively corresponding to H2O2/endogenous Fe/EDTA molar ratio of 20/1/1. The optimized H2O2 dose was in good agreement with the predicted higher H2O2 levels in further works Watts et al. (2002); Goi and Trapido (2004) An increase in the amount of H2O2 promotes the increase of OH radicals and consequently the output of petroleum hydrocarbons elimination. Pardo et al. (2014) noted that the increase in H2O2 amount of simple to double improves TPHS removal efficiency in the case of polluted soil by mixture of biodiesel and diesel. Mater et al. (2007) and Villa et al. (2008) also observed an improvement of organic compounds degradation effectiveness for high concentrations in H2O2.
Fig. 6. a Surface plot of effects of H2O2 and total iron doses on TPHS removal efficiency. b Surface plot of effects of total iron and EDTA doses on TPHS removal efficiency.
H. Ouriache et al. / Chemosphere 232 (2019) 377e386
385
TPH (%)
79,25557 ±7,459526
90 70 50 30
1
-1
-1
H2O2
ZVI
EDTA
1
0,75
0,5
0,25
1 0
0,5
0
-0,5
1 -1
0,5
0
-0,5
1 -1
0,5
0
-0,5
0 0,25 0,5 0,75 1 -1
Desirability 0,851126
10
Desirability
Fig. 7. Optimum FL process factors by desirability functions for maximum TPHs removal.
4. Conclusion The pretreatment of a soil prone to an old pollution by petroleum hydrocarbons, by FL oxidation without modification of pH, was studied. The experimentations results related to the influence of H2O2 and iron showed poor yield of TPHs degradation (29.0 ÷ 39.3%), probably because of soil matrix characteristics, age of the pollution but also the weak mass transfer in solid phase reactor. The addition of a chelating agent, the EDTA improved considerably the oxidation of TPHs up to 72.2% for a ratio (H2O2/ total iron/EDTA)molar of 15/4/4 after 48 h of treatment. The use of the factorial design on two levels, has allowed the determination and the optimization of the potentially influential factors and interactions and to provide a model of prediction of the FL oxidation process in the established study domain. Endogenous iron was sufficient to catalyze H2O2 and to support TPHS oxidation up to 79.3 ± 7.5% for a molar ratio H2O2/endogenous iron/EDTA of 20/1/1. The desirability function highlighted that the maximum elimination efficiency was expected with a desirability of 0.85 under optimized condition. References Benatia, C.T., Costa, A.C.S., Tavares, C.R.G., 2009. Characterization of solids originating from the Fenton's process. J. Hazard Mater. 163, 1246e1253. Bergendhal, J.A., Thies, T.P., 2004. Fenton's oxidation of MTBE with zero-valent iron. Water Res. 38, 327e334. Catrouillet, C., Davranche, M., Dia, A., Coz, M.B.-L., Marsac, R., Pourret, O., Gruau, G., 2014. Geochemical modeling of Fe(II) binding to humic and fulvic acids. Chem. Geol. 372, 109e118. Cheng, M., Zeng, G., Huang, D., Lai, C., Xu, P., Zhang, C., Liu, Y., 2016a. Hydroxyl radicals based advanced oxidation processes (AOPs) for remediation of soils contamined with organic compound : a review. Chem. Eng. J. 284, 582e598. Cheng, M., Zeng, G., Huang, D., Lai, C., Xu, P., Zhang, C., Liu, Y., Wan, J., Gong, X., Zhu, Y., 2016b. Degradation of atrazine by a novel Fenton-like process and assessement the influence on the treated soil. J. Hazard Mater. 312, 184e191. Colombo, R., Ferreira, T.C.R., Alves, S.A., Carneiro, R.L., Lanza, M.R.V., 2013. Application of the response surface and desirability design to the Lambadacyhalothrin degradation using photo-Fenton reaction. J. Environ. Manag. 118, 32e39. Ferrarese, E., Andreottola, G., Opera, I.A., 2008. Remediation of PAH-contaminated sediments by chemical oxidation. J. Hazard Mater. 152, 128e139. Flotron, V., Delteil, C., Padellec, Y., Camel, V., 2005. Removal of sorbed polycyclic aromatic hydrocarbons from soil, sludge and sediment samples using the Fenton's reagent process. Chemosphere 59, 1427e1437. Gan, S., Yap, C.L., Ng, H.K., Venny, 2013. Investigation of the impacts of ethyl lactate based Fenton treatment on soil quality for polycyclic aromatic hydrocarbons (PAHS)-contaminated soils. J. Hazard Mater. 262, 691e700. Goi, A., Trapido, M., 2004. Degradation of polycyclic aromatic hydrocarbons in soil: the Fenton reagent versus ozonation. Environ. Technol. 25, 155e164. Goi, A., Kulik, N., Trapido, M., 2006. Combined chemical and biological treatment of
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