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Abstract

Due to the extreme toxicity of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/F), the remediation of PCDD/F aquifer source zones is greatly needed; however, it is very difficult due to their persistence and recalcitrance. The potential degradability of PCDD/F bound to a real matrix was studied in five systems: iron in a high oxidation state (ferrate), zero-valent iron nanoparticles (nZVI), palladium nanopowder (Pd), a combination of nZVI and Pd, and persulfate (PSF). The results were expressed by comparing the total toxicity of treated and untreated samples. This was done by weighting the concentrations of congeners (determined using a standardized GC/HRMS technique) by their defined toxicity equivalent factors (TEF). The results indicated that only PSF was able to significantly degrade PCDD/F. Toxicity in the system decreased by 65% after PSF treatment. Thus, we conclude that PSF may be a potential solution for in-situ remediation of soil and groundwater at PCDD/F contaminated sites.
DOI: 10.1515/eces-2016-0034 ECOL CHEM ENG S. 2016;23(3):473-482
Pavel HRABÁK
1
, Martina HOMOLKOVÁ
1*
, Stanisław WACŁAWEK
1
and Miroslav ČERNÍK
1
CHEMICAL DEGRADATION OF PCDD/F
IN CONTAMINATED SEDIMENT
CHEMICZNA DEGRADACJA PCCD/F
W ZANIECZYSZCZONYM SEDYMENCIE
Abstract: Due to the extreme toxicity of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/F), the
remediation of PCDD/F aquifer source zones is greatly needed; however, it is very difficult due to their persistence
and recalcitrance. The potential degradability of PCDD/F bound to a real matrix was studied in five systems: iron
in a high oxidation state (ferrate), zero-valent iron nanoparticles (nZVI), palladium nanopowder (Pd),
a combination of nZVI and Pd, and persulfate (PSF). The results were expressed by comparing the total toxicity of
treated and untreated samples. This was done by weighting the concentrations of congeners (determined using
a standardized GC/HRMS technique) by their defined toxicity equivalent factors (TEF). The results indicated that
only PSF was able to significantly degrade PCDD/F. Toxicity in the system decreased by 65% after PSF
treatment. Thus, we conclude that PSF may be a potential solution for in-situ remediation of soil and groundwater
at PCDD/F contaminated sites.
Keywords: PCDD/F, ferrate, nZVI, Pd, persulfate, degradation
Introduction
Polychlorinated dibenzo-p-dioxins (PCDD) and polychlorinated dibenzofurans (PCDF)
are without doubt the highest priority groups of pollutants. They belong to the first groups
of pollutants (called the Dirty Dozen) to be inscribed under the Stockholm Convention on
Persistent Organic Pollutants (POPs) in 2001. The aim of this convention is to protect
human health and the environment from harmful and widely distributed chemicals by
requiring its parties to eliminate or reduce the release of POPs into the environment [1].
Contrary to all other POPs, PCDD/F were never intentionally produced as
organochlorinated pesticides as they are exclusively impurities/by-products with a varying
origin. PCDD/F are highly toxic for human health and wildlife, remain intact in the
environment for long periods of time, are widely distributed throughout the environment,
and bioaccumulate in fatty tissues of humans and animals. Their toxic effect is mediated
1
Faculty of Mechatronics, Informatics and Interdisciplinary Studies & the Institute for Nanomaterials, Advanced
Technologies and Innovation, Technical University of Liberec, Studentská 1402/2 Liberec, 46117, Czech
Republic, phone +420 485 353 848, fax +420 485 353 696
*
Corresponding author: martina.homolkova@tul.cz
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through the interaction with an intracellular protein, the aryl hydrocarbon receptor (AHR)
[2], which occurs in most vertebrate tissues and affects a number of other regulatory
proteins. The toxicity of PCDD/F depends on the number and position of the chlorine
atoms in their molecule. Congeners with chlorines in the 2, 3, 7, and 8 positions have the
highest affinity to the AH receptor and are therefore significantly harmful. Seven dioxins
and ten furans have chlorines in these relevant positions and are considered toxic by the
WHO-TEQ scheme (World Health Organization Toxic Equivalent) [2]. The most toxic
dioxin is reported to be 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), which is the strongest
known human carcinogen according to the International Agency for Research on Cancer
[3]. On the contrary, PCDD/F containing between one and three chlorine atoms are not
considered to be toxicologically serious, whereas other organic molecules, for example
coplanar PCB or polychlorinated naphthalenes, possess dioxin-like toxicity [4, 5].
The WHO-TEQ scheme was adopted internationally as the most appropriate way of
estimating the potential health risks of mixtures of PCDD/F as there are 75 PCDD and
135 PCDF possible congeners. The total TEQ value expresses the total sample toxicity as if
only TCDD congener would be present. Each of the seven dioxin and ten furan toxic
congeners is given a toxicity ranking called the toxic equivalency factor (TEF) from 0 to 1,
where the reference congener is TCDD which by definition has a TEF = 1. Their
concentration is then weighted by their TEF, which gives a congener contribution to the
sample TEQ. Alternatively to calculating the specific congener contributions after
GC/HRMS determination, a screening method based on cell-line with sensitized AHR
could be used [4].
The remediation of PCDD/F contaminated soil is generally very difficult.
Post-excavation soil cleaning methods mostly employ physical or chemical methods like
thermal treatment [6, 7], surfactant washing [8, 9] or base-catalysed decomposition [10] of
PCDD/F.
In this paper, we studied the potential degradation of PCDD/F bound to a real soil
matrix by applying five different oxidants and reductants with a potential for in-situ
remediation. Two extreme oxidation states of iron were tested: Fe
0
nanoparticles
(zero-valent iron nanoparticles, nZVI) and Fe
+6
(ferrate, Fe(VI)). Ferrate is a very strong
oxidant whose superior performance for environmental remediation has been demonstrated
in various recent researches [11-13]. On the other hand, ZVI in the form of nanoparticles is
a strong reductant with a large specific surface and has been utilized for groundwater
remediation and wastewater treatment [14, 15]. The second metal having a potential
dechlorination capability was the catalytic, noble metal palladium in the form of
a nanopowder. A combination of Pd and nZVI was also studied as it has been reported that
such a combination improves the degradation rates of chlorinated compounds [16, 17]
including PCDD/F [18, 19]. Finally, heat-activated PSF was tested as sulfate and hydroxyl
radical generator. SO
4•-
and OH
are one of the strongest known oxidants used for in situ
chemical oxidation in the remediation of soil and groundwater [20].
Materials and methods
Chemicals
PCDD/F was used in the form of an industrial sandy soil certified reference material
(BCR 529) [21] obtained from Sigma Aldrich. Information on the presence of the certified
concentrations of PCDD/F is given in Table 1. The certified values were not available for
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all of the congeners presented in the material; however, the concentrations of the other
congeners were determined through analysis and were in good agreement with the data
obtained by Antunes et al [22]. The toxicity equivalent factors (TEF) [23] used for dioxins
are also given in Table 1.
Table 1
Composition of the certified reference material [21] and the TEF values [23]
PCDD/F (#) Certified value
[µg/kg] Uncertainty
[µg/kg] TEF
2,3,7,8-TCDD (D1) 4.5 0.6 1
1,2,3,7,8-PeCDD (D2) 0.44 0.05 0.5
1,2,3,4,7,8-HxCDD (D3) 1.22 0.21 0.1
1,2,3,6,7,8-HxCDD (D4) 5.4 0.9 0.1
1,2,3,7,8,9-HxCDD (D5) 3.0 0.4 0.1
1,2,3,4,6,7,8-HpCDD (D6) - - 0.01
OCDD (D7) - - 0.001
2,3,7,8-TCDF (F1) 0.078 0.013 0.1
1,2,3,7,8-PeCDF (F2) 0.145 0.028 0.05
2,3,4,7,8-PeCDF (F3) 0.36 0.07 0.5
1,2,3,4,7,8-HxCDF (F4) 3.4 0.5 0.1
1,2,3,6,7,8-HxCDF (F5) 1.09 0.15 0.1
2,3,4,6,7,8-HxCDF (F6) 0.37 0.05 0.1
1,2,3,7,8,9-HxCDF (F7) 0.022 0.010 0.1
1,2,3,4,6,7,8-HpCDF (F8) - - 0.01
1,2,3,4,7,8,9-HpCDF (F9) - - 0.01
OCDF (F10) - - 0.001
Potassium ferrate was provided by the company LAC. The content of Fe was
determined by elemental analysis as being 25.5% Fe. Room temperature
57
Fe Mossbauer
spectroscopy determined the iron oxidation states as follows: 5% Fe(V), 7% Fe(VI) and
88% of Fe(III). This implies that the ferrate powder contained 5.5% K
3
FeO
4
and
6.5% K
2
FeO
4
.
Standard NANOFER 25P nZVI (NANO IRON, s.r.o., Olomouc, Czech Republic) was
used in the form of a dry powder preserved in an inert nitrogen atmosphere. The particles
were without surface modification and had an average size of 50 nm, average surface area
of 20-25 m
2
/g and a narrow size distribution of 20-100 nm. The content of iron was high,
ranging between 80 and 90 wt. %. An aqueous suspension of Fe
0
was prepared from the
powder at a ratio of 1:4 nZVI:water, which yielded a suspension with an nZVI content of
200 g Fe
0
/dm
3
.
Palladium nanopowder (< 25 nm) with purity 99.9% was obtained from Aldrich.
Sodium persulfate (PSF) of p.a. quality was obtained from Penta.
Methods
A total of 1.0 g of the certified BCR-329 material was placed into each reactor
containing 522.5 cm
3
of demineralized water and stirred vigorously for 30 minutes. After
that, the appropriate reactant (Fe(VI), nZVI, Pd, Pd+nZVI and PSF) was added. The
reaction times differed in accordance to the reactant used. The dosed amounts of the
individual chemicals together with durations of reactions are summarized in Table 2. The
reaction of PCDD/F with Fe(VI) and nZVI was performed in triplicate and the reaction
with Pd, Pd+nZVI and PSF in duplicate. The base samples consisting of water and PCDD/F
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only were repeated nine times in total with reaction times ranging from 3 to 60 days, thus
covering all of the different reaction times used in this study. PSF was activated by heat,
namely at 50°C, during the whole reaction time.
Table 2
Dosed amounts and the reaction times
Reaction time
*
Fe(VI) nZVI Pd PSF
Base 3-60 days - - - -
Fe(VI) 3 days 1.0 g - - -
nZVI 60 days - 5.0 g - -
Pd 22 days - - 0.1 g -
Pd+nZVI 22 days - 5.0 g 0.1 g -
PSF 7 days - - - 10.0 g
*
reaction times were chosen on the previous experience with reagents reactivity - no remaining reducing/oxidizing
effect is supposed to persist in reactors at the end of the reaction time
Analytical methods
The samples were processed in a commercial laboratory (ALS) by the standard
extraction and cleaning procedure for PCDD/F, including the addition of the appropriate
13
C
12
labelled internal standards according to EN 1948-2 [24]. The separation, identification
and determination of PCDD/F in the extracts containing the standards for determining the
recoveries were performed using GC/HRMS according to EN 1948-3 [25]. The seventeen
congeners listed in Table 1 were determined.
Results and discussion
For clarity and simplification, all of the results were expressed as toxicity equivalency
values (TEQ), which is a summary parameter evaluating the congener concentration
weighted by its TEF.
The composition of the base samples was determined and the results were expressed as
TEQ of each PCDD/F congener in each base sample as shown in Figure 1. Furthermore, the
TEQ contribution of each average PCDD/F congener to the overall toxicity of the average
base sample is shown in Figure 2. The total TEQ of the average base was determined
as 11.138 ng/g.
It is apparent from Figure 2 that almost two thirds (specifically 6.8 ng/g, which
corresponds to 61.1%) of the overall TEQ resulted from the D1 congener. The other
relatively high contributions (but significantly lower in comparison to D1) were 7.4% and
6.0% for D4 and D6, respectively. The lowest TEQ was exhibited by F1, F2 and F9.
PCDD/F samples were treated by iron in its two extreme oxidation states, Fe
0
(nZVI)
and Fe
+6
(Fe(VI), ferrate), by palladium nanopowder (Pd), by a combination of Pd with
nZVI and by PSF. The overall results of this study are summarized in Figure 3 where the
columns represent summary TEQ values of all of the congeners. With the exception of the
PSF treated samples, no significant degradation of the sum of PCDD/F was observed for
any of the reactants. A distinct decrease in the overall PCDD/F toxicity and thus overall
PCDD/F content was caused solely by PSF. This decrease was from 11.1 to 3.9 ng/g, which
corresponded to 65%.
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Fig. 1. TEQ of individual congeners in base samples
Fig. 2. Contribution of individual congeners to the overall toxicity of the base
Contrary to the PSF treated sample and to our presumption, the TEQ in ferrate treated
samples increased. This could be explained by the ferrate oxidation of the real matrix
containing PCDD/F, which could help/contribute to the release of PCDD/F bound to the
matrix and thus a higher extraction yield could have been caused. However, the increase in
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TEQ may also have been caused solely by experiment error, as the difference between the
base and ferrate treated samples is within the range of standard deviation. The relatively
high standard deviation ranges in the case of the ferrate and nZVI treated samples could be
explained by difficult dosing of these two particular chemicals due to their inhomogeneity.
In the case of ferrate, the inhomogeneity lies in the solid sample itself which was dosed;
whereas nZVI was dosed in the form of an aqueous suspension, which is known to solve
the problem of nZVI sedimentation and/or aggregation [26]. Neither nZVI (despite the
highly reactive pyrophoric form used), nor Pd, nor even their combination, caused any
significant degradation. As mentioned above, according to Kim et al [18], the combination
of nZVI and Pd rapidly dechlorinates PCDD. However, in their study bimetallic palladized
nanosized ZVI (Pd/nFe) was used. In contrast, only a simple mixture of nZVI and
nanosized Pd was used in our experiment. This fact may explain our negative result, as such
a contact between the two surfaces was not achieved in our study.
Fig. 3. Summary of the whole study expressed in TEQ values (mean ± standard deviation)
The behavior of the individual congeners in the PSF treated samples and their
contribution to the overall decline in TEQ are shown in Figure 4. The rate of decline
differed for each PCDD/F congener; however, it is apparent that there was a decrease in
each of them. No increase in the concentration of any of the congeners was observed. The
most significant contribution to the overall decrease was exhibited by congeners D1, D2
and D4. When taking into account the relative values, the highest relative decline was
observed for D2, F1 and F2, which decreased by 97.1, 91.4 and 85.3%, respectively;
whereas the lowest observed decline was 28.5, 47.0 and 47.5% for F8, D6 and D7,
respectively. One can conclude that high reactivity of PSF towards PCDD/F congeners can
be due to the high reaction rate between both sulfate and hydroxyl radicals and the electron
rich bonds in aromatic rings [27, 28].
As there was a different rate of decline of each PCDD/F congener after PSF treatment,
their relative contribution to the overall toxicity of the sample changed (Fig. 5) compared to
the base sample (Fig. 2). The highest contribution, more than one half, was still
conclusively caused by D1, but the others did not lag so far behind this time. The highest
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contributions to the total TEQ of PSF treated samples were 53.8, 9.5 and 9.0% for D1, D4
and D6, respectively.
Fig. 4. Decline of individual congeners in the PSF treated samples (mean ± standard deviation)
Fig. 5. Contribution of individual congeners to the overall toxicity of PSF treated samples
Only a few studies are comparable with our system. Kim et al [29] described
approximately 15% TCDD degradation in a heat-activated persulfate system. In contrast to
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the real soil matrix that we report here, Kim et al [29] dosed TCDD as being solvent-
dissolved and started the reaction after complete acetone evaporation.
The behavior of individual congeners and their contribution to the overall PCDD/F
TEQ increase in Fe(VI) treated samples is shown in Figure 6. It can be assumed that the
overall behavior was caused mostly by D1 and partly by D4. Other congeners with
increasing concentrations were D3, D5, D7, F2, F6 and F10. On the other hand, there are
also congeners with decreasing concentrations. The highest relative decrease was observed
in the case of F9 and F5 with 23.7 and 20.0%, respectively.
Fig. 6. Behavior of individual congeners in the Fe(VI) treated samples (mean ± standard deviation)
Conclusions
In this paper the potential degradation of PCDD/F bound to a real matrix was studied
by five different oxidants and reductants commonly used for in-situ remediation, ie Fe(VI),
nZVI, Pd, Pd+nZVI and PSF. We conclude that only the treatment by sulfate and hydroxyl
radicals formed in the heat-activated PSF system exhibited a significant decrease in the
PCDD/F concentrations. This decrease was 65% when comparing the total toxicity of the
base and the treated samples. Thus, PSF activated at 50°C may be used for the remediation
of aquifers contaminated by these priority pollutants. Future research should be devoted to
studying wider range of activation temperatures, whereby the lower ones are of much
technological interest. Other PSF activation procedures (electroactivation, alkaline
activation or hydrogen peroxide activation as examples) have also a potential to create
strongly mineralising conditions applicable for PCDD/F degradation.
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Acknowledgements
The work was supported by the project OPR&DI of the Centre for Nanomaterials,
Advanced Technologies and Innovation (CZ.1.05/2.1.00/01.0005), the National Programme
for Sustainability I (LO1201) and by the Ministry of Education, Youth and Sports of the
Czech Republic through the SGS project 21066/115.
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... Several researchers have reported that the application of persulfate along with activating methods such as heat, UV, Fe (0/II), etc. showed an effective performance for the treatment of soil contaminant, and the advantages of using persulfate, such as a long half-life (600 days at 25°C), and high oxidation power (SO 4 %− /SO 4 2− , E 0 = 2.44 V), have been prevalently studied [4][5][6][7][8][9][10][11][12][13][14]. Although many studies of persulfatebased treatment were reported, there are very few studies of the persulfate oxidation for soil PCDD/Fs treatment [15,16]. Due to the serious toxicity of PCDD/Fs, the regulatory standards (Table S1) of all countries are designated as scale of pg·g soil −1 , and this extremely low level of standards cause the technical and cost problems in the precise analysis, which precludes PCDD/Fs from being comprehensively studied [2,17]. ...
... Hence, there are very few studies of soil PCDD/Fs treatment using persulfate. The work of Kim et al. [15] and Hrabák et al. [16] are the ones most relevant to the soil treatment using persulfate. The degradation of single PCDD/F species on glass beads, to simulate soil particles, using thermally activated persulfate was conducted by Kim and his co-workers. ...
... As the temperature becomes higher, the PCDD/Fs degradation strayed from a pseudo first-order reaction. It was previously reported that the degradation of PCDD/Fs via S 2 O 8 2− activated by thermal energy follows a pseudo first-order reaction, and the aspect of a PCDD/Fs degradation reaction would be changed after a certain amount of intermediates were formed [15,16]. S 2 O 8 2− activation by heat [34,35] and Fe 2+ [29,36] have been studied by several researchers, and they have reported that the activation by Fe 2+ is faster than by heat. ...
Article
The uses of Fe²⁺ and thermal energy as S2O8²⁻ activating methods for the treatment of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) contaminated soil using S2O8²⁻ were simultaneously studied for the first time. PCDD/Fs degradation was conducted using S2O8²⁻ with and without the Fe²⁺ addition at 25 °C, 40 °C, and 60 °C, and the process of S2O8²⁻ without Fe²⁺ showed the best performance, 99.0% removal efficiency of 17 PCDD/Fs in 72 h. The SO4⁻ based process is effective for the degradation of PCDD/Fs. The presence of Fe²⁺ greatly influenced the soil pH development during the process, but the pH change showed an insignificant effect on PCDD/Fs degradation by the SO4⁻ based process. The performances of several options implied that the direct interactions of Fe²⁺, heat, and S2O8²⁻ on PCDD/Fs are very few, and interestingly, the combination of Fe²⁺ and thermal energy did not always show a clear advantage over the individual use of Fe²⁺ or thermal energy. The behaviours of PCDD/Fs in S2O8²⁻ based process is consistent regardless of an activating method. The lower-chlorinated PCDD/Fs were easier to be degraded than higher ones, and in most cases, more PCDFs were degraded than PCDDs in the case of same chlorine numbers.
... Peroxydisulfate (PDS, persulfate) is one of the most commonly used precursors of sulfate radicals for ISCO (in-situ chemical oxidation). It is also relatively cheap compared to other oxidants used in ISCO and possesses unique properties that may help suppress POPs resistant to other AOP treatments [5]. ...
Article
Peroxydisulfate (PDS) is a commonly used oxidant for in-situ chemical oxidation. There is still a lack of reliable methods for PDS determination, especially in the presence of other strong oxidants or other anions. Therefore, a new method was developed based on the evolution of a stable oxidation product from Acid Blue 40 (AB40) dye. The procedure was assessed in terms of its effectiveness for PDS determination in complex matrices, e.g., containing other oxidants. It was proven that the AB40 molecule selectively reacts with the sulfate radical, generated from PDS by heat activation, whereas it is inert towards other oxidants such as hydrogen peroxide, peroxymonosulfate ion or calcium peroxide. Mass spectrometry analysis, combined with theoretical investigations (density functional theory), confirmed the mechanism of this reaction and the product responsible for the color generation. The effect of AB40 concentration, activation temperature, presence of common anions, pH and other parameters were evaluated and a suitable analytical procedure for the PDS detection has been proposed. The limits of detection and quantification were determined to be 2 µM and 2.5 µM, respectively, which makes this method one of the most sensitive in the scientific literature for PDS determination. It is believed that this method may be very easily (colorimetry), quickly (30 min) and effectively used for groundwater and wastewater that possess complicated matrices.
... They have a higher oxidation-reduction potential than Mn(VII)/Mn(IV), Cr(VI)/Cr(III) ( Table 2) or commonly used oxidants (e.g. ozone, hydrogen peroxide, chlorine, perchlorate, hypochlorite) and can be therefore applied for remediation of drinking and wastewater [38,39]. Ferrates can be photoreduced to Fe(V) to produce an even stronger oxidant than Fe(VI) [40]. ...
Article
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Polycyclic aromatic hydrocarbons (PAHs) are a common part of the environment where they come from burning fossil fuels (through an incomplete combustion process). From a toxicological point of view, PAHs are considered to be carcinogens with a mutagenic and teratogenic effect. On the other hand, ferrates are generally believed to be the ideal chemical agent for water treatment due to their strong oxidation potential. Herein, the efficiency of degradation of PAHs (with the special emphasis on B[a]P) by ferrates under laboratory conditions was studied. The formation of degradation products was also considered. For this, two types of ferrates were used and both of them efficiently degraded B[a]P. When comparing ferrates that were bought from a Czech and USA company, no significant changes in terms of B[a]P degradability were observed. It was determined that the degradation efficiency of PAHs by ferrates was dependent on their molecular weight. Two and three cyclic PAHs have been completely degraded within 30 minutes, whereas five (and more) cyclic PAHs, only partially. The results obtained with ferrates were compared to the ones obtained with a classical oxidizing agent - KMnO4. In a qualitative test to detect degradation products of PAHs, two were identified, namely fluoren-9-one derived from fluorene and acentaphthylene, formed from acenaphthene.
... Recently, the use of ferrates VI as a water treatment to oxidise organic pollutants (laboratory experiments) has been well documented. This strong oxidant reacts on a wide range of agents as pharmaceuticals, pesticides, phenols, cyanide, heavy metals, microorganisms, natural organic matter (Bielski et al. 1994;Filip et al. 2011;Gan et al. 2015;Hrabak et al. 2016;Jiang et al. 2006;Johnson and Sharma 1999;Liu et al. 2019;Manoli et al. 2019;Peings et al. 2017Peings et al. , 2015Rai et al. 2018;Sharma 2013Sharma , 2008Yngard et al. 2008) and aromatic structures like BTEX (Lacina and Goold 2015;Pepino Minetti et al. 2017), water lixiviates from bitumen and PAHs (Guan et al. 2014). It releases O 2 , HO − and ends as Fe (OH) 3, which has flocculent properties and is nontoxic towards the environment. ...
Article
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In situ chemical oxidations are known to remediate PAH contaminations in groundwater and soils. In this study, batch-scale oxidations aim to compare the PAC (polycyclic aromatic compound) degradation of three oxidation processes traditionally applied for soil treatment: permanganate, heat-activated persulfate (60 °C) and Fenton-like activated by magnetite, to results obtained with ferrates (FeVI). Widely studied for water treatments, ferrates are efficient on a wide range of pollutants with the advantage of producing nontoxic ferric sludge after reaction. However, fewer works focus on their action on soil, especially on semi-industrial grade ferrates (compatible with field application). Oxidations were carried out on sand spiked with dense non-aqueous phase liquid (DNAPL) sampled in the groundwater of a former coking plant. Conventional 16 US-EPA PAHs and polar PACs were monitored, especially potential oxygenated by-products that can be more harmful than parent-PAHs. After seven reaction days, only the Fenton-like showed limited degradation. Highest efficiencies were obtained for heat-activated persulfate with no O-PAC ketones formed. Permanganate gave important degradation, but ketones were generated in large amount. The tested ferrates not only gave slightly lower yields due to their auto-decomposition but also induced O-PAC ketone production, suggesting a reactional pathway dominated by oxidoreductive electron transfer, rather than a radical one.
... As a common remediation technology, ISCO can effectively degrade most organic pollutants or decrease their toxicity by adding chemical agents directly into contaminated soil or groundwater [13,14]. Oxidants used in ISCO include potassium permanganate, Fenton's reagent and ozone [15,16], and persulfate [17][18][19][20]. The persulfate ion (S 2 O 8 2− ) has a standard redox potential of 2.01 V (Equation (1)), which is close to that of ozone (2.07 V) and higher than that of permanganate (1.68 V) and hydrogen peroxide (1.70 V) [21]. ...
Article
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In situ injection of Fe(II)-activated persulfate was carried out to oxidize chlorinated hydrocarbons and benzene, toluene, ethylbenzene, and xylene (BTEX) in groundwater in a contaminated site in North China Plain. To confirm the degradation of contaminants, an oxidant mixture of persulfate, ferrous sulfate, and citric acid was mixed with the main contaminants including 1,2,3-trichloropropane (TCP) and benzene before field demonstration. Then the mixed oxidant solution of 6 m3 was injected into an aquifer with two different depths of 8 and 15 m to oxidize a high concentration of TCP, other kinds of chlorinated hydrocarbons, and BTEX. In laboratory tests, the removal efficiency of TCP reached 61.4% in 24 h without other contaminants but the removal rate was decreased by the presence of benzene. Organic matter also reduced the TCP degradation rate and the removal efficiency was only 8.3% in 24 h. In the field test, as the solution was injected, the oxidation reaction occurred immediately, accompanied by a sharp increase of oxidation–reduction potential (ORP) and a decrease in pH. Though the concentration of pollutants increased due to the dissolution of non-aqueous phase liquid (NAPL) at the initial stage, BTEX could still be effectively degraded in subsequent time by persulfate in both aquifers, and their removal efficiency approached 100%. However, chlorinated hydrocarbon was relatively difficult to degrade, especially TCP, which had a relatively higher initial concentration, only had a removal efficiency of 30%–45% at different aquifers and monitoring wells. These finding are important for the development of injection technology for chlorinated hydrocarbon and BTEX contaminated site remediation.
... Cai et al. [58] proved that the bimetallic Fe-Co/GAC catalyst may be utilized to heterogeneously activate SPS oxidation for Acid Orange 7 degradation, which has also been proven in other studies. Also, very toxic persistent organic pollutants (POPs) can be decontaminated with persulfates [59]. ...
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Although the use of ferrate (VI), an emerging green oxidant, has been widely investigated to remove organic pollutants in water, its ability to remediate contaminated soils has been scarcely evaluated. Here, we explore the use of ferrate (VI) to degrade a polychlorinated persistent compound, the pentachlorophenol (PCP), in aqueous solution and in an aged contaminated soil under batch, water-saturated and water-unsaturated flow conditions. The first results showed the prominent efficiency of ferrate (VI) over conventional oxidants (e.g. H2O2 and persulfate) in both matrices and at different oxidant doses. In aqueous solution, more than 80% of PCP was degraded by ferrate (VI) while complete removal was observed in soil under batch conditions. In column experiments, PCP removal by ferrate (VI) remained efficient but dependent on the flow rate and water saturation. Maximum PCP removal (95%) in columns was observed under water saturated conditions when ferrate (VI) (0.2 g g⁻¹ of soil) was injected at a low flow rate (i.e. 0.025 mL min⁻¹). This study has strong implications in the development of new sustainable processes based on ferrate (VI) for the remediation of different environmental compartments.
Chapter
Basic chemistry and water treatment of broad range of oxidants and related radical species are covered in this chapter. A general introduction to oxidants and radicals is followed by detailed sections on chlorine species, advanced oxidation processes, persulfates, and non-consensual radical mechanisms. Further, detailed information on oxidant applicability and activation, oxidant-specific recalcitrant pollutants and commonly formed by-products is provided. To assess the suitability of the specific oxidants for real water conditions, matrix components interferences are discussed. Considerable attention is paid to chemistry of innovative oxidants (persulfates) and to the controversial aspects of superoxide radical anion reactivity with carbon tetrachloride.
Chapter
For several years now, many substances that are known for saving the lives of billions of people, have paradoxically appeared as a new group of very dangerous contaminants. These compounds (for example, pharmaceuticals, pesticides, their metabolites, etc.) often have chronic and acute dangerous effects on humankind and other living beings. The presence of these pollutants is being documented and novel systems are being developed for their treatment every day. In this chapter, we review the literature from approximately the past 10 years, illustrating the decontamination of these chemicals by advanced oxidation processes (AOPs). A range of methods including novel catalytic systems for hydroxyl radical production as well as computation methods for prediction of CEC removal rate constants and their transformations are discussed. Furthermore, many (bio)transformation (by)products possess different (lower/higher) toxicological fingerprints, which can now also be assessed by advanced modelling. Moreover, many of these AOPs are limited commercially by their high capital and operating costs. All of these issues are addressed in this book chapter.
Article
Lindane (γ-hexachlorocyclohexane) and its isomers (HCH) are some of the most common and most easily detected organochlorine pesticides in the environment. The widespread distribution of lindane is due to its use as an insecticide, accompanied by its persistence and bioaccumulation, whereas HCH were disposed of as waste in unmanaged landfills. Unfortunately, certain HCH (especially the most reactive ones: γ- and α-HCH) are harmful to the central nervous system and to reproductive and endocrine systems, therefore development of suitable remediation methods is needed to remove them from contaminated soil and water. This paper provides a short history of the use of lindane and a description of the properties of HCH, as well as their determination methods. The main focus of the paper, however, is a review of oxidative and reductive treatment methods. Although these methods of HCH remediation are popular, there are no review papers summarising their principles, history, advantages and disadvantages. Furthermore, recent advances in the chemical treatment of HCH are discussed and risks concerning these processes are given.
Article
Catalytic reductive dechlorination of monochlorobenzene(MCB) was carried out in the palladium/iron system. With low Pd loading (0.005%), 45% dechlorination efficiency was achieved within 5 h. Pd as catalyst accelerated the reductive dechlorination reaction. Dechlorination mechanism and kinetics were discussed. The reaction took place on the bimetal surface in a pseudo-first-order reaction, with the rate constant being 0.0071 min(-1) ( K-SA = 8.0 x 10(-3) L/(m(2.)h). The reduction product for MCB was benzene.
Article
Ferrate(VI) ion has the formula FeO42−, and possesses unique properties, vs. strong oxidising potential and simultaneous generation of ferric coagulating species. For this reason, a number of studies have been carried out to investigate the preparation, characterisation and application of ferrate(VI) for water and wastewater treatment. These studies revealed that ferrate(VI) can disinfect microorganisms, partially degrade and/or oxidise organic and inorganic impurities, and remove suspended/colloidal particulate materials in a single dosing and mixing unit process. Most recently, research groups globally have reported using ferrate(VI) to treat emerging micropollutants in water purification processes. Work has not only been limited to fundamental studies but has been driven by the ideas of putting the application of ferrate(VI) into practice; the advantages of the application of ferrate(VI) over existing water and wastewater treatment methods should be shown as should other benefits to the water industry of its use. This paper thus reviews advances in the preparation and use of ferrate(VI), discusses the potential full scale application of ferrate(VI) in water purification and recommends required future research in order to implement ferrate(VI) in practice. © 2013 Society of Chemical Industry
Article
In this paper, flotation in acidic conditions and alkaline leaching soil washing processes were compared to decontaminate four soils with variable contamination with metals, pentachlorophenol (PCP), and polychlorodibenzo dioxins and furans (PCDD/F). The measured concentrations of the four soils prior treatment were between 50 and 250 mg/kg for As, 35 and 220mg/kg for Cr, 80 and 350mg/kg for Cu, and 2.5 and 30mg/kg for PCP. PCDD/F concentrations reached 1394, 1375, 3730, and 6289ng/kg for F1, S1, S2, and S3 soils, respectively. The tests were carried out with masses of 100g of soil (fraction 0-2 mm) in a 2 L beaker or in a 1 L flotation cell. Soil flotation in sulphuric acid for 1 h at 60 degreeC with three flotation cycles using the surfactant cocamidopropyl betaine (BW) at 1% allows the solubilization of metals and PCP with average removal yields of 85%, 51%, 90%, and 62% for As, Cr, Cu, and PCP, respectively. The alkaline leaching for 2 h at 80 degreeC solubilizes As, Cr, Cu, and PCP with average removal yields of 60%, 32%, 77%, and 87%, respectively. Tests on PCDD/F solubilization with different surfactants were carried out in combination with the alkaline leaching process. PCDD/F removal yields of 25%, 72%, 70%, and 74% for F1, S1, S2, and S3 soils, respectively, were obtained using the optimized conditions.
Article
Recent industrial and urban activities have led to elevated concentrations of a wide range of contaminants in groundwater and wastewater, which affect the health of millions of people worldwide. In recent years, the use of zero-valent iron (ZVI) for the treatment of toxic contaminants in groundwater and wastewater has received wide attention and encouraging treatment efficiencies have been documented. This paper gives an overview of the recent advances of ZVI and progress obtained during the groundwater remediation and wastewater treatment utilizing ZVI (including nanoscale zero-valent iron (nZVI)) for the removal of: (a) chlorinated organic compounds, (b) nitroaromatic compounds, (c) arsenic, (d) heavy metals, (e) nitrate, (f) dyes, and (g) phenol. Reaction mechanisms and removal efficiencies were studied and evaluated. It was found that ZVI materials with wide availability have appreciable removal efficiency for several types of contaminants. Concerning ZVI for future research, some suggestions are proposed and conclusions have been drawn.
Article
Rate coefficients published in the literature on hydroxyl radical reactions with pesticides and related compounds are discussed together with the experimental methods and the basic reaction mechanisms. Recommendations are made for the most probable values. Most of the molecules whose rate coefficients are discussed have aromatic ring: their rate coefficients are in the range of 2×109–1×1010 mol–1 dm3 s–1. The rate coefficients show some variation with the electron withdrawing–donating nature of the substituent on the ring. The rate coefficients for triazine pesticides (simazine, atrazine, prometon) are all around 2.5×109 mol–1 dm3 s–1. The values do not show variation with the substituent on the s-triazine ring. The rate coefficients for the non-aromatic molecules which have C=C double bonds or several C–H bonds may also be above 1×109 mol–1 dm3 s–1. However, the values for molecules without C=C double bonds or several C–H bonds are in the 1×107–1×109 mol–1 dm3 s–1 range.
Article
Persulfate is the newest oxidant that is being used for in situ chemical oxidation (ISCO) in the remediation of soil and groundwater. In this review, the fundamental reactions and governing factors of persulfate relevant to ISCO are discussed. The latest experiences for ISCO with persulfate are presented, with a focus on the different activation methods, the amenable contaminants, and the reactions of persulfate with porous media, based primarily on a critical review of the peer-reviewed scientific literature and to a lesser extent on non-reviewed professional journals and conference proceedings. The last sections are devoted to identifying the best practices based on current experience and suggesting the direction of future research.