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DDT-Contaminated Soil Treatment with Persulfate and Hydrogen Peroxide Utilizing Different Activation Aids and the Chemicals Combination with Biosurfactant

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The efficacy of DDT-contaminated soil treatment with hydrogen peroxide and persulfate utilizing different activation aids and the chemicals combination with biosurfactant was evaluated. The addition of a supplementary activator was able to improve the degradation of total DDT with both the hydrogen peroxide and persulfate oxidation processes indicating a lack of available activator. Ferrous iron added gradually was effectively utilized in the oxidation system with gradual addition of hydrogen peroxide, while chelated metal iron addition promoted the oxidation with more stable persulfate. The treatment with solid carriers of hydrogen peroxide, either calcium peroxide or magnesium peroxide, can be an effective alternative to the liquid one resulting in a higher degradation level of the contaminant. Strong alkalization with elevated dosages of NaOH sustained the persulfate oxidation of DDT. The addition of biosurfactant, rhamnolipid-alginate complex obtained by biosynthesis of strain Pseudomonas sp. PS-17, and EDTA improved the degradation of DDT by both persulfate and hydrogen peroxide oxidation processes indicating that the combined application of chemical oxidants and biosurfactant at natural soil pH has prospects as an effective option for contaminated soil remediation.
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ISSN 1203-8407 © 2012 Science & Technology Network, Inc. J. Adv. Oxid. Technol. Vol. 15, No. 1, 2012 41
DDT-Contaminated Soil Treatment with Persulfate and Hydrogen
Peroxide Utilizing Different Activation Aids and the Chemicals
Combination with Biosurfactant
Anna Goi*, 1, Marika Viisimaa1, and Oleksandr Karpenko2
1Department of Chemical Engineering, Tallinn University of Technology, Ehitajate tee5, Tallinn 19086, Estonia
2Department of Technology of Biologically Active Substances, Pharmacy and Biotechnology, Lviv Polytechnic
National University, Banery 12, Lviv 79013, Ukraine
Abstract:
The efficacy of DDT-contaminated soil treatment with hydrogen peroxide and persulfate utilizing different
activation aids and the chemicals combination with biosurfactant was evaluated. The addition of a supplementary
activator was able to improve the degradation of total DDT with both the hydrogen peroxide and persulfate
oxidation processes indicating a lack of available activator. Ferrous iron added gradually was effectively utilized
in the oxidation system with gradual addition of hydrogen peroxide, while chelated metal iron addition promoted
the oxidation with more stable persulfate. The treatment with solid carriers of hydrogen peroxide, either calcium
peroxide or magnesium peroxide, can be an effective alternative to the liquid one resulting in a higher degradation
level of the contaminant. Strong alkalization with elevated dosages of NaOH sustained the persulfate oxidation
of DDT. The addition of biosurfactant, rhamnolipid-alginate complex obtained by biosynthesis of strain
Pseudomonas sp. PS-17, and EDTA improved the degradation of DDT by both persulfate and hydrogen peroxide
oxidation processes indicating that the combined application of chemical oxidants and biosurfactant at natural
soil pH has prospects as an effective option for contaminated soil remediation.
Keywords: soil decontamination; biosurfactant; chelated iron; hydrogen peroxide solid carrier; base activated
persulfate
Introduction
DDT (2,2-bis(p-chlorophenyl)-1,1,1-trichloroethane)
is the key compound in the group of the organochlorine
pesticides, which proved to have detrimental environ-
mental effect and concern as persistent toxic pollutant.
DDE (2,2-bis(p-chlorophenyl)-1,1-dichloroethylene)
and DDD (2,2-bis(p-chlorophenyl)-1,1-dichloroethane)
exist as impurities in technical-grade DDT formulations
and form as a result of the abiotic transformation,
aerobic biotic degradation and photochemical de-
composition of DDT (1). The combined concentration
of DDT and its metabolites in a sample is generally
denoted as total DDT (2). In spite of the reduction in
the production and use accompanied by bans and
other restrictions, DDT remains widely dispersed in
the environment. It happens due to long-range atmo-
spheric transport processes, sea currents and local “hot
spots”. Moreover, DDT low solubility and bioavaila-
bility resist the application of many conventional
treatment methods for its degradation.
Chemical oxidation is an innovative technology of
degrading an extensive variety of hazardous compounds
*Corresponding author; E-mail address: Anna.Goi@ttu.ee
for the treatment of soil at waste disposal and spill
sites. Among the chemicals, hydrogen peroxide is one
of the most extensively used for the treatment of
contaminated soil (3). Another promising approach
could be combined application of biosurfactants and
chemical oxidants. There are several studies (4-6),
where synthetic surfactants of Triton X group were
used in order to enhance the degradation of DDT and
its metabolites (DDD, DDE) in water and soil by the
treatment methods mostly utilizing zero-valent iron. In
spite of the surfactants ability to improve substantial
the DDT solubility, some of synthetic surfactants (or
their degradation by-products) could become potential
contaminants in surface and groundwater. The applica-
tion of biosurfactants that are biologically produced
by bacteria or yeast from various substrates including
sugars, oil alkanes and wastes (7) can be even more
effective due to their apparent advantages over the
extensively used synthetic surfactants including high
specificity, biodegradability and biocompatibility (8).
Previously, it has been found (9) that the addition
of biosurfactant and acetone could enhance DDT,
DDD and DDE release to bulk solution facilitating the
dechlorination of the contaminants in soil slurry with
magnesium/palladium system. Thus, biosurfactants
42 J. Adv. Oxid. Technol. Vol. 15, No. 1, 2012
may also potentially act as stimulators of the chemical
oxidation processes, increasing contaminants avai-
lability to oxidizing agents as the oxidation processes
mainly occur (10) in liquid phase.
DDT-contaminated soil washing with non-ionic
synthetic surfactant Triton X-100 with the following
separation of the liquid phase and its treatment by the
photo-Fenton was found (11) to be effective for the
soil decontamination. However, reports evaluating the
potential of the combined application of chemical
oxidants and biosurfactants that due to their bio-
degradability, low toxicity and high efficiency in
various conditions can substitute their synthetic
counterparts in the environmental applications have
not been published to date. Moreover, if simultaneous
application of biosurfactants and chemical oxidants
without solid-liquid separation will be effective, then
such a process modification would provide the treat-
ment cost reduction and the increase of the subsurface
treatment efficacy.
Proper selection of the remedial chemical and the
activation aid is also of a great importance for the
effective oxidation of contaminants in soil. Few studies
(12, 13) have evaluated the potential of the activated
hydrogen peroxide oxidation process applied for DDT-
contaminated soil remediation. They demonstrated the
efficacy of DDT-contaminated soil treatment with the
hydrogen peroxide oxidation process activated by
supplementary ferrous iron. However, the requirement
for acidic conditions needed to keep iron soluble limits
the utility of ferrous iron to activate the hydrogen
peroxide oxidation for contaminated soil remediation
at natural soil pH that lies usually in the range of 4-8
(14). A chelation of natural metal ions of soil can
promote the chemical oxidation of contaminants in a
wider pH range. Thus, the potential and efficacy of the
hydrogen peroxide oxidation process activated by a
chelated iron in DDT-contaminated soil treatment
should be evaluated.
In addition, there are no published studies on
DDT-contaminated soil treatment with solid carries of
hydrogen peroxide such as calcium and magnesium
peroxides. The treatment process utilizes liquid carrier
of hydrogen peroxide has several disadvantages such
as violent exothermic reaction and a rapid consumption
of the oxidant. These disadvantages were also
emphasized in the study of Villa et al. (13) on the
hydrogen peroxide treatment of DDT-contaminated
soil. The application of the solid carriers of hydrogen
peroxide that have a benefit of slow hydrogen peroxide
release (15) achieved during their contact with percola-
tion water of soil can solve the mentioned drawbacks.
Persulfate, another newest chemical oxidant recently
received attention due to its increased stability in the
subsurface (16) should also be considered as an
alternative to hydrogen peroxide for DDT-contaminated
soil treatment.
Therefore, the main goals of the present study were
1) to evaluate and compare the individual chemical
(persulfate, liquid carrier of hydrogen peroxide and
solid carriers of hydrogen peroxide - calcium peroxide
and magnesium peroxide) impact on DDT-contam-
inated soil treatment; 2) to test different activation aids
(supplemental application of non-chelated/chelated
ferrous and ferric iron, chelation of natural transition
metals of soil, base activation of persulfate, combined
application of persulfate and hydrogen peroxide,
application of acidic pH conditions to sustain the
persulfate and hydrogen peroxide activation processes)
as the application of that depends not only on the
remedial chemical used, but also on the target
contaminant; and 3) to resolve the benefits of the
combined treatment with biosurfactant, rhamnolipid-
alginate complex obtained by biosynthesis of strain
Pseudomonas sp. PS-17, and the chemicals.
Experimental and Methods
Soil Sample Preparation and Characterization
Natural topsoil (0-20 cm) was dried over-night at
30 °C in a circulating air-dryingoven before the spiking
and sieved through a 30 mm sieve using a Retsch (AS
200) digital sieve shaker. Several characteristics of the
soil are presented in Table 1. Ferrous iron and ion-
exchangeable Fe(II) fractions were extracted according
to the procedure presented by Tessier et al. (17). Total
extractable iron of the soil was extracted according to
Heron et al. (18). Iron in the extracts was measured
photometrically at 492 nm with phenanthroline method
(19). Soil pH was measured according to EPA method
9045C (20) using a digital pH meter (CG-840, Schott)
equipped with a Mettler Toledo InLaB 412 electrode.
Organic carbon of the soil was determined by sulfo-
chromic oxidation (21). The identification of soil
texture was based on the principles established by ISO
14688-1,2 (22, 23) using a laser scattering particle size
distribution analyzer (LA-950, Horiba). The texture of
the soil was identified as the sandy silt.
Soil Contaminant
Dry soil was spiked with a commercial preparation
of organochloride pesticide DDT (1 g of product
contained 0.273 g of total DDT: 0.187, 0.058 and
0.028 g of DDT, DDD and DDE, respectively) by
adding contaminant-acetone solution. Acetone, pur-
chased from Rathburn, was evaporated to dryness
under a continuous mixing to ensure the contaminant
J. Adv. Oxid. Technol. Vol. 15, No. 1, 2012 43
Table 1. Several characteristics of the untreated soil.
Parameter, unit Value
(mean ± standard deviation)
pH 5.88
Ferrous iron fraction (g kg-1 of soil) 1.9 ± 0.5
Total extractable iron (g kg-1 of soil) 12.1 ± 0.9
Ion-exchangeable Fe(II) fraction (mg kg-1 of soil) 2.0 ± 0.3
Organic carbon (mg kg-1 of soil) 460 30
Sand (%) 45.5
Silt (%) 52
Clay (%) 2.5
distribution homogeneity and, hence, a better reproduc-
ibility in repeated experiments. The contamination
was aged for 120 d. Combine concentration of DDT
and its metabolites (DDD and DDE), denoted as total
DDT concentration, was found to be 1.719 ± 0.288 g
kg-1 of soil. The initial concentrations of DDT, DDD
and DDE, verified by the analysis of eleven replicates,
were 1.159 ± 0.207, 0.423 ± 0.103, 0.137 ± 0.059 g kg-1
of dry soil, respectively. Contaminants recovery was
87 ± 14%.
Soil Treatment
Biosurfactant solution (pH of 7) was added in
different concentrations to the soil (solid/liquid ratio of
1/2, w/v) 24 h prior the chemicals addition. No mixing
was applied within the following 24 h. The bio-
surfactant was rhamnolipid-alginate complex obtained
(24, 25) by biosynthesis of strain Pseudomonas sp.
PS-17 (the collection of microorganisms of the
Department of Physicochemistry of Combustive
Minerals of L.M. Litvinenko Institute of Physical-
Organic and Coal Chemistry of the National Academy
of Sciences of Ukraine). The complex was isolated
from cultural liquid via acidic precipitation in form of
50% concentrate.
Sodium peroxodisulfate (Na2S2O8, min 99%),
purchased from Riedel-de Haën, calcium peroxide
(CaO2and Ca(OH)2mixture, powder, 200 mesh (0.075
mm), commercially available product) and magnesium
peroxide (MgO2and MgO mixture, powder, 100 mesh
(0.152 mm) with 50% min through 200 mesh (0.075
mm), commercially available product), purchased from
Aldrich, and hydrogen peroxide (35%), purchased from
Sigma-Aldrich, were used as the remedial chemicals.
The measured (15) contents of CaO2in calcium
peroxide and MgO2in magnesium peroxide products
were 76.4 ± 0.1% (with 17.0 0.1% w/w of available
oxygen) and 11.6 ± 0.1% (with 3.3 0.1% w/w of
available oxygen), respectively.
The FeSO4·7H2O and Fe2(SO4)3·2H2O salts,
purchased from Sigma-Aldrich, were used as sup-
plementary activator sources. Ferrous iron chelated
with EDTA for the activation of the hydrogen peroxide
or persulfate oxidation of DDT in soil was also tested.
A stock solution of Fe(II)-EDTA with chelate/Fe2+
weight ratio of 1/5 was prepared by first dissolving of
EDTA with EDTA disodium salt/EDTA tetrasodium
salt weight ratio of 2/1 and then of ferrous sulfate. The
appropriate volume of the stock solution was added to
the slurry achieving the desired dose. For the chelating
of natural activators present in soil, EDTA (EDTA
disodium salt/EDTA tetrasodium salt weight ratio of
2/1) solution (stock solution with the concentration of
EDTA 0.1 g L-1) utilizing the same dose as in the
experiments with Fe2+-EDTA complex was added 30
min prior the application of the oxidizing chemicals.
The examination of pH effect was carried out by
adjusting of soil slurry pH with H2SO4or NaOH.
The chemical treatment of DDT-contaminated soil
in slurry was carried out with different soil/chemical
weight ratios (w/w) in a batch mode. The standard
procedure was that slurry of 10 g soil with 30 mL
liquid (biosurfactant solution and/or bi-distilled water
and solutions of the chemicals) was treated in the
cylindrical glass reactor with a 0.2-L of volume under
a vigorous (300 rpm) magnetic-stirring during 24 h. In
the experiments on the metal ion activated persulfate
or hydrogen peroxide oxidation of DDT, activator
(ferrous iron, ferric iron or chelated ferrous iron)
solution was first added all at once or gradually (2
additions: 0, 4 h) and then the reaction was initiated
by single or gradual (2 additions: 0, 4 h) addition of
the chemicals solution.
In the experiments on the treatment of 60%-watered
soil with calcium and magnesium peroxides, 10 g of
moist (with 60% of double-distilled, autoclaved water)
soil were mixed with the calcium peroxide or
magnesium peroxide technical products (powder) and
then treated without the pH pre-adjustment and stirring
44 J. Adv. Oxid. Technol. Vol. 15, No. 1, 2012
in the cylindrical glass reactor with a 0.2-L of volume
for 24 h.
The flasks were sealed with a laboratory film
(Parafilm) to reduce volatilization losses. All experi-
ments were carried out in duplicates at 20 1C.
Results are presented with ± standard deviation of the
mean.
Chemical Analysis
After the treatment, the solid phase was settled for
30 min and the supernatant was separated and filtrated
(paper filter, Filtrak 160). The solid phase was dried
with anhydrous Na2SO4, obtained from Lach-Ner.
Dried soil with the filter was soaked in 10 mL of n-
hexane/acetone (1/1, v/v) and placed for the extraction
to a laboratory reciprocal shaker (358S, Elpan)
overnight. Then, a vortex (IKA, Genius3) extraction
procedure three times (30 mL of n-hexane/acetone of
1/1 v/v each time) per 2 min was used. Joined extracts
were evaporated dry and the residue was dissolved in
1 mL of acetone and 1 mL of n-hexane with internal
standard. The internal standard was hexadecane dis-
solved in n-hexane with the concentration of 0.2 g L-1.
Similar extraction procedure was applied for the initial
untreated soil. The liquid phase separated after the soil
treatment was vortex extracted with two portions of n-
hexane/acetone (1/1, v/v) for 2 min. Joined extracts
were mixed (1/1, v/v) with the internal standard.
The measurement of total DDT (DDT and its
metabolites - DDD, DDE) was carried out using a
FocusGC, Finnigan GC-FID (Thermo Electron
Corporation). 2 L were injected splitless in a cross-
bond 100% dimethylpolysiloxane capillary column
RTX-1 (30 m x 320 m id x 0.25 m film thickness).
The injector temperature was set to 230 C. The GC
temperature program started at 40 ºC, the initial
temperature was held for 1 min then increased by 10
ºC min-1 to 270 ºC, and held for 3 min. The detector
temperature was 330 C. The velocity of carrier gas
(nitrogen) was 1 mL min-1. External standard was
prepared by dissolving DDT, DDD, DDE standards
(99% purity, Supelco) in a mixture (1/1, v/v) of n-
hexane and acetone. The detection limit of the method
was 20.6 mg DDE, 23.6 mg DDD and 26.2 mg DDT
L-1 of solvent that corresponds to 4.1 mg DDE, 4.7 mg
DDD and 5.2 mg DDT kg-1 of dry soil. Contaminants
concentration in soil was calculated per dry weight.
The GC-FID analyses of un-spiked soil did not show
any content of contaminants.
Residual hydrogen peroxide in the supernatant
treated by titanium sulfate with pertitanic acid forma-
tion was measured photometrically at 410 nm (26).
Residual persulfate was detected photometrically
(Heλios UV-vis spectrophotometer, Thermo Electron
Corporation) at 446 nm as o-dianisidine-peroxydi-
sulfate complex (27). pH after the treatment was
measured using a digital pH meter (CG-840, Schott)
equipped with a Mettler Toledo InLaB 412 electrode.
Residual ferrous iron concentration in the
supernatant was measured photometrically (Heλios
UV-vis spectrophotometer, Thermo Electron Corpora-
tion) at 492 nm by means of 1,10-phenanthrolinium
chloride (19).
Results and Discussion
Persulfate and/or Hydrogen Peroxide Oxidation
of DDT
The results of the present study showed (Figure 1)
that total DDT (DDT, DDD, DDE mixture) in soil
could degrade to some level (33 ± 2% of total DDT
residual) with the addition of hydrogen peroxide only
indicating a possible ability of soil natural minerals or
transition metals chelated by natural soil chelating
agents, (such as organic acids, amino acids and
hydroxamate siderophores of soil) either applied or
produced by plants or microorganisms, to activate the
hydrogen peroxide oxidation of DDT at natural (Table
1) soil pH. A potential of naturally occurring minerals
and transition metals of soil to activate the hydrogen
peroxide oxidation was indicated in several studies
(28-31) and the reaction mechanism in mineral-
catalyzed Fenton system was proposed (32).
DDT could also degrade with the addition of
persulfate only (Figure 1). It is known (33) that the
persulfate decomposition is extremely sensitive even
to the traces of metal ions. In spite of in the study of
Ahmad et al. (34) was found that soil minerals did not
promote the generation of oxidants and reductants
during the persulfate decomposition, the degradation
of contaminants in soil by persulfate addition alone
was also observed in theother studies (35).
The degradation of total DDT in soil with either
hydrogen peroxide or persulfate was uncompleted and
independent of the chemicals dosages used, resulting
in the same level of DDT removal (Figure 1). After a
24-h treatment with persulfate the DDT removal was
slightly (by 5%) higher than that with hydrogen
peroxide applying similar dosages of the chemicals
(Figure 1). While hydrogen peroxide was completely
decomposed during a 24-h treatment independent of
the dosage used, the persulfate was found to be more
stable. 37, 67, 75 and 79% of the initially applied
persulfate remained after a 24-h treatment of soil with
the weight ratios of soil/persulfate of 1/0.00012,
1/0.0012, 1/0.0024 and 1/0.0037, respectively.
Consumption ofpersulfate, calculated in g of persulfate
J. Adv. Oxid. Technol. Vol. 15, No. 1, 2012 45
0
10
20
30
40
50
60
70
80
90
100
1/0.00012
1/0.0006
1/0.0012
1/0.0024
1/0.0037
1/0.0006/0.0006
1/0.0012/0.0012
1/0.0024/0.0024
soil/hydrogen peroxide or persulfat e, g/g soil/hydrogen
peroxide/persulfate, g/g/g
Removal, %
hydrogen peroxide
persulfate
Table 2. pH after a 24-h treatment with persulfate and hydrogen peroxide.
Soil/chemical/Fe2+, w/w/w pH after the treatment with
persulfate pH after the treatment
with hydrogen peroxide
1/0.0006/0 5.62 6.45
1/0.0012/0 5.54 6.70
1/0.0024/0 5.25 6.80
1/0.0037/0 5.18 6.89
1/0.0012/0.00012 5.25 6.19
1/0.0012/0.00024 4.74 5.25
1/(0.0006 + 0.0006)/(0.00012 + 0.00012) 5.45 5.42
1/0.0006/0, initial pH of 3.5 4.13 3.79
1/0.0012/0, initial pH of 3.5 4.31 4.25
1/0.0024/0, initial pH of 3.5 4.58 4.27
Figure 1. Total DDT removal (% of initial, mean standard
deviation) after a 24-h treatment of soil at natural soil pH with
hydrogen peroxide and/or persulfate at different weight ratios of
soil/chemical.
decomposed per g of DDT degraded, increased with
the ratios of soil/persulfate applied. For example, 0.12,
0.63, 0.90 and 1.1 g of S2O82- were consumed per g of
DDT degraded within 24 h of the treatment at soil/
persulfate ratios of 1/0.00012, 1/0.0012, 1/0.0024 and
1/0.0037, respectively. The loss of the chemicals
without the degradation of the contaminant could be
explained by the competing reactions (3, 33, 36) such
as non-productive chemicals decomposition without the
generation of oxidants, reaction with the soil organic
matter and reduced minerals, etc. Thus, the increased
consumption of persulfate and hydrogen peroxide at
equal level of DDT removal makes no sense in
application of elevated loads of the chemicals.
The changes in the soil pH were not substantial
during the treatment with persulfate (Table 2). Even
the application of the highest dosage of persulfate
(soil/persulfate of 1/0.0037, g/g) resulted in only slight
pH drop from initial 5.88 to 5.18 within 24 h of the
treatment. It was emphasized in the study of Liang et
al. (37) on the persulfate treatment of trichloroethylene-
contaminated soil that soil buffering capacity usually
appeared sufficient to offer resistance to pH changes
during the persulfate decomposition. In contrast to the
persulfate treatment, a substantial increase in the pH
with the increasing of the hydrogen peroxide dosage
was observed (Table 2).
The treatment of soil with a dual chemicals system
utilizing both hydrogen peroxide and persulfate resulted
in a higher total DDT degradation level compared to
that obtained by the treatment with a single chemical
application (Figure 1). It was hypothesized (38) that the
combined usage of hydrogen peroxide and persulfate
may provide a multi-radical attack mechanism, yielding
a higher efficacy in destroying contaminants, or allow-
ing recalcitrant compounds to be more readily degraded.
A possible reaction mechanism was presented in the
study of Tsao and Wilmarth (39). It was suggested
that hydroxyl radicals can initiate sulfate radicals
formation, while sulfate radicals can stimulate produc-
tion of hydroxyl radicals (Eqs. 1-5).
S2O82- 2SO4-(1)
SO4-+ H2OH++ SO42- + OH(2)
OH+ H2O2H2O + HO2(3)
HO2+ S2O82- O2+ HSO4-+ SO42- (4)
HO2+ H2O2O2+ H2O + OH(5)
A two-fold increase of H2O2/S2O82-/soil weight
ratio from 0.0006/0.0006/1 to 0.0012/0.0012/1 slightly
(by 9%) improved the degradation of total DDT. No
effect of higher H2O2/S2O82-/soil = 0.0024/0.0024/1
weight ratio application on the DDT degradation was
observed. Near-complete (99%) decomposition of
hydrogen peroxide was achieved within a 24-h treat-
ment at all the ratios of chemicals applied. In addition,
91% (0.12 g of persulfate consumed per g of DDT
degraded) and 93% (0.17 g of persulfate consumed
per g of DDT degraded) of initially applied persulfate
46 J. Adv. Oxid. Technol. Vol. 15, No. 1, 2012
0
10
20
30
40
50
60
70
80
90
100
1/0.00016, slurry 1/0.00016, 60%
H2O 1/0.0006, slurry 1/0.0006, 60%
H2O
soil/chemical, g/g
Removal, %
calcium peroxide
magnesium peroxide
were decomposed within a 24-h treatment at the H2O2/
S2O82-/soil ratios of 0.0012/0.0012/1 and 0.0024/
0.0024/1, respectively. Thus, lower ratios of H2O2/
S2O82-/soil should be applied in order to avoid compet-
ing reactions (36) of hydrogen peroxide and persulfate
with oxidizing agents instead of target contaminant.
Some decrease in the pH after a 24-h treatment with
the increase of both, hydrogen peroxide and persulfate
dosages was observed. The pH values of 5.28, 5.18
and 4.96 were obtained after a 24-h treatment at the
soil/H2O2/S2O82- ratios of 1/0.0006/0.0006, 1/0.0012/
0.0012 and 1/0.0024/0.0024, respectively.
The application of hydrogen peroxide solid carriers,
either calcium peroxide or magnesium peroxide, known
as the sources of hydrogen peroxide produced during
their decomposition in contact with water (15, 40, 41)
resulted in higher DDT removal level comparing with
that achieved by the usage of the liquid carrier of
hydrogen peroxide. As can be seen in Figures 1 and 2,
the application of similar dosages of hydrogen peroxide
and calcium peroxide (soil/chemical of 1/0.0006, g/g)
for the soil treatment in slurry resulted in 35% and
83% of total DDT removal, respectively. It is known
(41) that the main advantage of the solid carrier of
hydrogen peroxide over the liquid one is the ability to
release H2O2slowly that reduces its non-productive
decomposition usually observed (32) during a non-
supplemented direct hydrogen peroxide application.
Thus, the hydrogen peroxide solid carriers (calcium
and magnesium peroxides) can be used as effective
alternatives to the liquid one for DDT-contaminated
soil treatment.
However, the degradation of total DDT was close
(Figure 2) at equal dosages of calcium peroxide and
magnesium peroxide (technical product) independent
of the active compound, CaO2and MgO2, content.
Moreover, similar to the treatment with hydrogen
peroxide or persulfate, the increase in the calcium
peroxide and magnesium peroxide dosages (the weight
ratio of soil/chemical decreased from 1/0.00016 to
1/0.0006) did not enhance the degradation resulting in
the same level of contaminant removal. The difference
in the pH, that found (15, 41) to have influence on the
treatment efficacy with solid carriers of hydrogen
peroxide, was insignificant after a 24-h treatment with
similar dosages of the chemicals. The pH values were
6.8 and 6.9 after a 24-h slurry treatment at the soil/
chemical ratio of 1/0.00016 with magnesium peroxide
and calcium peroxide, respectively. The increase of
the soil/chemical ratio to 1/0.0006 resulted in the pH
of 7.4 and 7.2 for the soil treated with calciumperoxide
and magnesium peroxide, respectively. Thus, slight
variations in the pH created (40) by the difference in
Figure 2. Total DDT removal (% of initial, mean standard
deviation) after a 24-h treatment of soil at natural soil pH in slurry
and of 60%-watered soil with calcium peroxide or magnesium
peroxide at different weight ratios of soil/chemical.
concentrations of both Ca(OH)2or Mg(OH)2released
and CaO2or MgO2loaded, did not influence the
efficacy of the treatment of DDT-contaminated soil.
However, a mode of the treatment (the treatment of
soil in slurry under a vigorous magnetic stirring or the
treatment of once pre-mixed 60%-watered soil)
considerably affected the treatment efficacy. A 24-h
treatment of soil in slurry with the hydrogen peroxide
solid carriers resulted in a higher degradation level of
DDT than that obtained by the treatment of 60%-
watered soil. This difference was probably achieved
by better desorption of the contaminant and/or natural
activator to the bulk solution and increased dissolution
rate of calcium and magnesium peroxides under
vigorous mixing conditions in slurry. The influence of
the hydrogen peroxide solid carrier dissolution rate on
contaminants degradation was also observed in the
studies of Goi et al. (15) and Xu et al. (42).
Hydrogen Peroxide and Persulfate Oxidation of
DDT Utilizing Supplementary Iron and/or
EDTA
Higher degradation level of total DDT was achieved
with addition of supplementary ferrous iron than that
obtained by persulfate or hydrogen peroxide addition
alone (Figures 3 and 4) suggesting a lack of available
activator, but not the oxidant. For example, a DDT
degradation level obtained by the treatment with non-
supplemented persulfate application (soil/S2O82- of
1/0.0006) was by 11% lower than that obtained by the
treatment with the persulfate oxidation activated by
supplementary ferrous iron (S2O82-/Fe2+ of 1/0.1)
(Figure 3). It should be noted that the consumption of
non-supplemented persulfate within 24 h of the treat-
ment was nearly twice as high as that of persulfate
activated by supplementary ferrous iron (Figure 5).
J. Adv. Oxid. Technol. Vol. 15, No. 1, 2012 47
0
10
20
30
40
50
60
70
80
90
100
1/0.1 1/0.1 1/0.02 1/0.1/0.02
S2O82- S2O82-/Fe2+ S2O82-/Fe3+ S2O82-/EDTA S2O82-
/Fe2+/EDTA
Weight ratio of chemicals added, g/g
Removal, %
soil/persulfate = 1/0.0006
soil/persulfate = 1/0.0024
0
10
20
30
40
50
60
70
80
90
100
1/0.1
1/0.2
1/0.1+0.1
0.5+0.5/0.2
0.5+0.5/0.1+0.1
1/0.1
1/0.2
1/0.02
1/0.04
1/0.1/0.02
1/0.2/0.04
H2O2 H2O2/Fe2+ H2O2/Fe3+ H2O2/EDTA H2O2/Fe2+/EDTA
Weight ratio of chemicals added, g/g
Removal, %
Figure 3. Total DDT removal (% of initial, mean standard
deviation) by a 24-h treatment of soil at natural soil pH with
persulfate applying ferrous iron, ferric iron, EDTA chelated ferrous
iron and EDTA only.
However, a double increase in supplementary ferrous
iron dosage (the ratio of persulfate/ferrous iron changed
from 1/0.1 to 1/0.2) not only reduced the degradation
of the contaminant, but also resulted in a complete
consumption of persulfate. Although gradual addition
of both persulfate and the activator during the treat-
ment with persulfate/ferrous iron of 1/0.2 allowed
reducing consumption of persulfate to 69% the degrada-
tion of DDT was not increased (Figure 5). Thus, an
excess in ferrous iron concentration can diminish
contaminant degradation efficacy during the persulfate
oxidation process. Similar observations were performed
by Liang et al. (43) in the study on trichloroethylene
degradation by persulfate in water, where the increase
in ferrous iron concentration resulted both in decreased
oxidation rate of the contaminant and increased
consumption of persulfate. A possible reason for that
can be an iron excess that can provide conditions for
increased quenching of oxidizing agents (sulfate and
hydroxyl radicals, e.g.). Residual dissolved ferrous
iron found in the bulk solution after a 24-h persulfate
treatment comprised of 0.5-3% of the initial load.
A two-fold increase in ferrous iron dosage (the
ratio of H2O2/Fe2+ changed from 1/0.1 to 1/0.2) with
hydrogen peroxide load remained invariable (soil/
hydrogen peroxide of 1/0.0012), favored the degrada-
tion of DDT with the activated hydrogen peroxide
oxidation process (Figure 4). A gradual addition of
both, hydrogen peroxide and ferrous iron resulted in
some (of 9%) improvement in the DDT degradation
level. The treatment with a gradual addition of hydrogen
peroxide or ferrous iron only was less effective than
that performed with the chemicals added in a single
manner or with gradual addition of both indicating
excess of either hydrogen peroxide or the activator. It
is known (36) that the degradation could be limited by
Figure 4. Total DDT removal (% of initial, mean standard
deviation) by a 24-h treatment of soil at natural soil pH with
hydrogen peroxide (soil/hydrogen peroxide of 1/0.0012, g/g)
applying ferrous iron, ferric iron, EDTA chelated ferrous iron and
EDTA only.
the quenching of OHwith hydrogen peroxide and
hydroperoxyl radicals in the presence of hydrogen
peroxide excess. Moreover, hydroxyl radical produc-
tion is also dependent on Fe2+/contaminant ratio that
determines the hydroxyl radical/contaminant ratio in
an initialrapid degradation phase (14).
While concentration of a residual dissolved ferrous
iron measured in the bulk solution after a 24-h treat-
ment with hydrogen peroxide and supplemental ferrous
iron comprised of 0.5-5% of the initial load value, a
residual hydrogen peroxide was not found. The pH
values measured after a 24-h treatment with either
hydrogen peroxide or persulfate (Table 2) were some-
what lower in the experiments with the addition of
supplementary ferrous iron than that obtained after the
treatment with the oxidizing chemical only.
Although Watts and Dilly (28) suggested that ferric
iron can be a more effective activator of the hydrogen
peroxide oxidation process due to its decreased demand
on hydrogen peroxide than the ferrous iron, the
addition of supplementary ferric iron did not improve
the DDT degradation by either the hydrogen peroxide
or persulfate oxidation process (Figs. 3 and 4). The
variations in dosages of the chemical (the case of
persulfate, Figure 3) or in dosages of ferric iron (the
case of hydrogen peroxide, Figure 4) did not affect
the degradation of DDT. Nevertheless, complete
decomposition of either persulfateor hydrogen peroxide
within a 24-h treatment was obtained indicating non-
productive consumption of the chemicals. Thus, the
application of ferric iron as an activator of the
persulfate or the hydrogen peroxide oxidation processes
was found to be useless in thepresent study.
While iron minerals can activate the hydrogen
peroxide oxidation of contaminants, they were found
(28-31) to be lees reactive than soluble iron. However,
it is known (36) that the iron efficiency as the
48 J. Adv. Oxid. Technol. Vol. 15, No. 1, 2012
38%
40%
47%
38%
69%
100%
43%
67%
0
10
20
30
40
50
60
70
80
90
100
1/0 1/0.1 1/0.2 0.5+0.5/0.1+0.1
persulfate/Fe2+,g/g
DDT removal or persulfatem
consumption,%
DDTdegradation
persulfate consumption
activator is also diminished with the decreasing of the
pH due to the reduction of iron solubility. Metal ions
chelation is known (14) to promote the chemical
oxidation of contaminants at natural soil pH. The
primary advantage of the metal ions complexes (44) is
the potential for effective generation of hydroxyl
radicals at near-neutral pH. Either chelated metal ion
complex can be supplementary added or transition
metals of soil can be chelated by a complexing agent
added. It was hypothesized (37) that chelator-extracted
native soil metals can be gradually released and served
as the activators for the persulfate oxidation of contam-
inant. In the study of Wu et al. (45) was also found
that EDTA can first chelate and then dissolute metals
considerably increasing total organic carbon content
in soil bulk solution without a substantial influence on
the pH. Dissolution mechanism of iron from iron
minerals can be classified according to the solutant
type and the reaction that takes place prior to dissolu-
tion. Three dissolution mechanisms were distinguished
(46): protonation, complexation, and reduction. The
potential mechanism of dissolution by complexation
was presented (47) on example of iron dissolved from
goethite by complex formation with salicylic acid.
The addition of a complexing agent EDTA for the
chelation of native transition metals of the soil substan-
tially improved the degradation of total DDT with the
hydrogen peroxide oxidation process (Figure 4) and
slightly influenced the degradation by persulfate (Figure
3). However, the increase in the ratio of soil/chemical
(in case of persulfate, Figure 3) or chemical/EDTA (in
case of hydrogen peroxide, Figure 4) did not result in
any considerable improvement in the degradation. A
lack of natural activator could possible diminish the
removal by both the persulfate and hydrogen peroxide
oxidation processes.
Complete consumption of persulfate was achieved
within 24 h of the treatment with supplementary
EDTA addition and the ratio of soil/persulfate =
1/0.0006. This is twice as high as persulfate consump-
tion (52%) obtained within 24 h of the treatment with
non-supplemented persulfate at same ratio of soil/
persulfate. Slightly higher persulfate consumption of
83% compared to that of 75% obtained in non-
accompanied system was achieved after a 24-h
persulfate treatment with supplementary EDTA addition
and the ratio of soil/persulfate of 1/0.0024. This increase
in persulfate consumption can be explained by an
enhanced release of total organic carbon to the bulk
solution that also was observed in the study of Wu et
al. (45) on the chelating of the soil metal ions by
EDTA. Thus, the increased background oxidant demand
could probably reduce the oxidation efficiency at
Figure 5. Total DDT removal (% of initial) and persulfate
consumption (% of initial) by a 24-h treatment of soil at natural
soil pH with persulfate (soil/persulfate of 1/0.0012, g/g) applying
supplementary ferrous iron.
higher dosages of chemicals applied. Although Liang
et al. (37) have also found that chelated native iron (or
other metal ions) was less effective than supplemental
chelated iron at enhancing of the persulfate oxidation
of contaminant; it can be to some extent useful (48)
for practical application.
While the persulfate oxidation of total DDT
activated by supplementary EDTA-chelated ferrous
iron was more effective than that by EDTA-native
transition metals complex or by supplementary soluble
ferrous iron activation aid, the hydrogen peroxide
oxidation activated by all the mentioned aids resulted
in equal total DDT degradation levels. In addition, the
persulfate treatment at a four-fold increase (from
0.0006/1 to 0.0024/1) of persulfate/soil weight ratio
and at invariable persulfate/metal ion activator
(supplementary unchelated ferrous iron, ferric iron,
chelated ferrous iron and chelated native iron or other
metal ions) ratio did not result in a higher DDT
degradation level (Figure 3).
Thus, possibly due to a lower stability of hydrogen
peroxide in the subsurface soluble ferrous iron added
gradually can be better utilized in the oxidation system
with gradual addition of hydrogen peroxide, while the
application of complexed metal activator can promote
the oxidation by more stable persulfate.
Complete consumption of persulfate was achieved
in the experiments with the application of the chelated
ferrous iron. Residual hydrogen peroxide was not
found in any of the experiments on metal activation of
the hydrogen peroxide oxidation. Opposite to the study
of Wu et al. (45) whereno any effectof EDTA addition
on the pH was observed, the pH increased after the
persulfate and hydrogen peroxide treatment in the
present study. For example, the application of a 24-h
persulfate treatment with the soil/S2O82-/EDTA ratios
J. Adv. Oxid. Technol. Vol. 15, No. 1, 2012 49
0
10
20
30
40
50
60
70
80
90
100
1/0.0006
1/0.0006 pH 3.5
1/0.0006 pH 9
1/0.0006 pH > 11
1/0.0012
1/0.0012 pH 3.5
1/0.0012 pH > 11
1/0.0024
1/0.0024 pH 3.5
1/0.0024 pH > 11
1/0.0006
1/0.0006 pH 3.5
1/0.0012
1/0.0012 pH 3.5
1/0.0024
1/0.0024 pH 3.5
so il/pers ulfate, g/g so il/hyd rogen pero xide, g /g
Removal, %
of 1/0.0006/0.000012 and 1/0.0024/0.000048 resulted
in the pH values of 6.53 and 6.44, respectively. The
pH values of 6.75 and 6.77 were obtained after the
hydrogen peroxide treatment with the soil/H2O2/EDTA
ratios of 1/0.0012/0.000024 and 1/0.0012/0.000048,
respectively. These values are higher than the values
obtained during the treatment with a single persulfate
application and close to that observed after the treat-
ment with a non-accompanied hydrogen peroxide
(Table 2).
Alkaline Activation of the Persulfate Oxidation
and the Influence of pH on the Hydrogen
Peroxide Oxidation
While strong alkaline conditions favored the oxida-
tion with persulfate, acidification to pH of 3.5 enhanced
the degradation of total DDT with the hydrogen
peroxide oxidation process (Figure 6).
For achieving basic pH needed for the activation
of persulfate NaOH, suggested (16) as a better choice
than KOH due to the precipitation of formed K2S2O8
[49], was added. A possible mechanism for base
activation of persulfate was recently proposed by
Furman et al. (50). An increase in the pH to a value of
9.0 could slightly (by 4%) improve the degradation of
the contaminant. Due to a strong buffering capacity of
the soil, the pH decreased during a 24-h treatment from
initial 9.0 to 7.6. The adjustment of the pH higher than
11, performed by the addition of NaOH at the weight
ratio of soil/NaOH = 1/0.01 (g/g), resulted in a higher
total DDT degradation level compared with that
achieved by the treatment at natural soil pH (Figure
6). However, the increase in the dosage of persulfate
(soil/persulfate weight ratio changed from 1/0.0006 to
1/0.0024) and decrease in the dosage of NaOH
(persulfate/NaOH molar ratio changed from 1/80 to
1/20) could diminish the degradation level of the
contaminant from 70 to 58%, respectively. Thus, for
the effective oxidation of contaminants in soil by base
activated persulfate, it is important to optimize not
only the ratio of soil/persulfate, but also the ratio of
persulfate/NaOH. Thus, elevated dosages of NaOH
that take into account the initial soil pH and its
buffering capacity should be applied in order to sustain
the base activated persulfate oxidation of contaminant.
Strong alkaline conditions (pH higher than 10) were
also recommended in other studies (16, 34, 38) on the
base activated persulfate oxidation. Complete consump-
tion of persulfate was achieved within 24 h of the
treatment in alkaline conditions at all the ratios of
soil/persulfate applied in the present study.
Slight improvement (from 4% at lower ratio of
soil/S2O82- = 1/0.0006 to 8% at higher ratio of soil/
Figure 6. Total DDT removal (% of initial, mean standard
deviation) by a 24-h treatment of soil with persulfate or hydrogen
peroxide at different initial values of pH and weight ratios of
soil/chemical.
S2O82- = 1/0.0024) in the degradation of total DDT
was also achieved by the persulfate treatment with a
pre-adjustment of the pH to a value of 3.5. It is known
(13, 35) that acidic conditions sustain the solubility of
natural soil metal mobilized during the strong chemicals
oxidation conditions involving them as the activators
of the oxidation process. As the system was not
buffered, the pH during the treatment somewhat
increased (Table 2) with the increasing of the persulfate
dosage.
The influence of the pH on the effectiveness of the
hydrogen peroxide oxidation was also investigated. As
a rule, acidic pH conditions of 2.0-4.0 favored the
oxidation of organic compounds, as it is known that
the decomposition rate of hydrogen peroxide reaches
the maximum in this pH range (51). This phenomenon
is attributed to the progressive hydrolysis of the ferric
iron, which provides a relatively large catalytically
active surface for contact with H2O2(52). The ferrous
iron ion accelerator will yield more hydroxyl radicals
in H2O2decomposition. Similar to the treatment with
persulfate, the pH during the hydrogen peroxide treat-
ment somewhat increased with the increasing of the
hydrogen peroxide dosage (Table 2). This slightly
reduced the degradation level of the contaminant
(Figure 6), as the productive utilization of hydrogen
peroxide may decrease (51) with the increasing of pH.
Complete consumption of either persulfate or
hydrogen peroxide was observed after a 24-h treatment
at the acidic pH conditions. However, comparing the
persulfate and the hydrogen peroxide oxidation systems,
a higher removal of total DDT was observed (Figure
6) during the treatment with the application of the
base activated persulfate utilizing similar dosages of
the chemicals.
50 J. Adv. Oxid. Technol. Vol. 15, No. 1, 2012
0
10
20
30
40
50
60
70
80
90
100
0 0.25 0.50 0.50 +
EDTA 0.75 1.0
Biosurfactant dose, g kg-1 of soil
Removal, %
hydrogen peroxide
persulfate
Coupling of Biosurfactant with the Persulfate
and the Hydrogen Peroxide Oxidation Systems
The addition of biosurfactant, rhamnolipid-alginate
complex obtained by biosynthesis of strain Pseudo-
monas sp. PS-17, improved the following degradation
of total DDT with both persulfate and hydrogen
peroxide (Figure 7). This improvement was probably
achieved by the contaminant enhanced desorption to
the liquid phase making it available to the oxidizing
agents. It was previously found (53) that the applied
biosurfactant could stimulate the biodegradation of
coal tar waste obtained from former gas work and
petroleum residue obtained from atmospheric distilla-
tion of light petroleum by increasing the coal tar
components bioavailability.
The chemical oxidation of the contaminant was
found to be dependent on the biosurfactant dosage
(Figure 7). Lower dosage (0.25 g kg-1 of soil) of the
biosurfactant did not show any improvement in the
degradation level of total DDT comparing with that
achieved by the treatment with hydrogen peroxide
applied alone. The doubling of the biosurfactant
dosage from 0.25 to 0.5 g kg-1 substantially (by 20%)
increased the degradation level. A further increase in
the biosurfactant dosage did not influence the efficacy
of the hydrogen peroxide oxidation process. The
efficacy of the persulfate oxidation was less dependent
on the biosurfacatant dosage comparing with that of
the hydrogen peroxide process. Although the lowest
biosurfactant dosage substantially improved the
persulfate oxidation of total DDT, further dosage
increase did not show any substantial improvement in
the efficacy. Moreover, some reduction in the degrada-
tion level was observed at the highest biosurfactant
dosage application. Thus, the optimal dosage of bio-
surfactant differed for the combined treatment utilized
hydrogen peroxide and for that utilized persulfate.
While residual hydrogen peroxide was not found
in any of the experiments on the hydrogen peroxide
treatment, the consumption of persulfate was strongly
increased along with dosage of the biosurfactant used.
Complete consumption of persulfate was achieved
within 24 h of the treatment utilizing the highest (1 g
kg-1 of soil) dosage of biosurfactant. In this case the
chemical could react with biosurfactant increasing the
unproductive decomposition of first along with the
dosage increase of last. In addition, a wide-range of
naturally occurring reactants other than the target
contaminant could also be desorbed to bulk solution
imposing the increased consumption of the chemical.
Solubility and availability of the transition metals
activators could be among the limiting factors in the
activation of persulfate and hydrogen peroxide by
Figure 7. Total DDT removal (% of initial, mean standard
deviation) by a 24-h treatment of soil at natural soil pH with
biosurfactant of different doses and persulfate or hydrogen
peroxide at weight ratio of soil/chemical of 1/0.0012. In the
experiment with supplementary EDTA the weigh ratio of
soil/EDTA of 1/0.000024 was used.
natural soil metals. There are several studies where
biosurfactants in addition to chelating agents were
effectively used for enhancing metal removal from
soil (54, 55). This gives a presumption for the addition
of biosurfactant and chelating agent to soil prior the
addition of the chemicals in order to sustain the
activation by chelated natural transition metals of soil.
As can be seen in Figure 7, the addition of the bio-
surfactant (0.5 g kg-1 of soil), EDTA, and the remedial
chemicals could improve thedegradation of the contam-
inant. Thus, the combined application of biosurfactant
for increasing of availability and solubility of both
contaminant and transition metals of soil, the chelating
agent for sustaining metal activity at natural soil pH
conditions and the chemicals (persulfate and hydrogen
peroxide) for the oxidation of contaminants can be an
effective option for contaminated soil remediation.
Conclusions
The application of optimized dosages of the
chemicals with the properly selected activator aid was
found to be important for the effective treatment of
contaminated soil with persulfate and hydrogen
peroxide.
Total DDT (DDT, DDD, DDE mixture) in soil
could degrade with the addition of persulfate or
hydrogen peroxide only indicating the potential ability
of transition metal ions and minerals of these metals
presented in soil to activate the oxidation at natural
soil pH (pH of 5.8). However, the degradation of total
DDT in soil was uncompleted and independent of the
chemicals dosage used.
Higher degradation of total DDT compared to that
obtained by persulfate or hydrogen peroxide addition
alone was achieved with the addition of supplementary
J. Adv. Oxid. Technol. Vol. 15, No. 1, 2012 51
metal activator suggesting a lack of available activator.
The use of ferric iron for activation of the persulfate
and the hydrogen peroxide oxidation processes did not
improve the degradation. While the activation of
persulfate by supplementary EDTA-chelated ferrous
iron was more effective than by EDTA-native transition
metal complex, the treatment efficacy of hydrogen
peroxide activated by either of aids was comparable.
However, a gradual addition of both hydrogen peroxide
and soluble ferrous iron improved the degradation.
Thus, added gradually soluble ferrous iron could be
effectively utilized in the oxidation system with a
gradual addition of hydrogen peroxide, while chelated
metal activator promoted the oxidation by more stable
persulfate.
The degradation of DDT by a 24-h treatment with
persulfate was slightly (by 5%) higher than that with
the hydrogen peroxide at similar dosages of the
chemicals used. The degradation of DDT with a dual
remedial chemical system utilizing both hydrogen
peroxide and persulfate was more effective than that
with a single chemical application.
The treatment with a solid carrier of hydrogen
peroxide, either calcium peroxide or magnesium
peroxide, can be an effective alternative to the liquid
one resulting in even higher degradation level of the
contaminant. A mode of the treatment with the solid
carrier of hydrogen peroxide considerably affected the
treatment efficacy. A 1-d treatment of soil in slurry
with the solid carrier of hydrogen peroxide under a
vigorous stirring resulted in a more efficient DDT
removal than that in 60%-watered soil.
While acidic p H conditions (pH 3.5) promoted the
total DDT degradation with hydrogen peroxide, strong
alkaline condition (pH higher than 11) with elevated
dosages of NaOH effectively sustained the activated
persulfate oxidation of the contaminant.
The addition of biosurfactant, rhamnolipid-alginate
complex obtained by biosynthesis of strain Pseudo-
monas sp. PS-17, and EDTA improved the degradation
of DDT with both persulfate and hydrogen peroxide at
natural soil pH. Thus, the treatment with the combined
application of biosurfactant for increasing of availa-
bility and solubility of both contaminant and transition
metals of soil, the chelating agent for sustaining metal
activity at natural soil pH conditions, and the
chemicals (persulfate and hydrogen peroxide) for the
oxidation of contaminants could be a promising option
for the contaminated soil remediation.
Acknowledgements
The financial support of the Estonian Ministry of
Education and Research (Target Financing Project
SF0140002s12) and the Estonian Science Foundation
(grant ETF 7812) is gratefully acknowledged. We
would like to thank M.Sc. degree student Anastassija
Gazejeva for the experimental assistance. Dr.Oleksandr
Karpenko is grateful to the Archimedes Foundation
and the European Social Fund for the participation in
the Internationalization Program DoRa, activity 5
“Facilitating international research cooperation by
supporting short-term research projects of visiting
doctoral students in Estonia”.
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Received for review August 4, 2011. Revised manuscript
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Supplementary resource (1)

... Surfactants can be divided into cationic surfactants, anionic surfactants, nonionic surfactants and zwitterionic surfactants according to whether the hydrophilic group is ionized in the aqueous solution and the type of charge carried by the molecule after ionization. Among them, sodium dodecyl sulfate (SDS), as a representative of anionic surfactants, is often used to extract pollutants such as chlorinated solvents (Huang et al., 2020), polycyclic aromatic hydrocarbons (Edwards et al., 1991), naphthalene (Rouse et al., 1993) and cresols (Gitipour et al., 2014). The solubilization principle of surfactants is that the solubility of hydrophobic organics in the surfactant aqueous solution increases with the increase of the surfactant concentration. ...
... Therefore, ISCO technology is often combined with surfactant solubilization remediation technology (S-ISCO) (Goi et al., 2012;Fei et al., 2016), that is, first solubilizing the pollutants in the low permeability soil phase into the water phase and then use ISCO technology to completely degrade the pollutants. S-ISCO technology exerts the advantages of the two remediation technologies and overcomes their respective limitations to achieve the purpose of improving remediation efficiency and reducing the costs and preventing secondary pollution. ...
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In this study, the common chlorinated solvent trichloroethene (TCE) was selected as the target contaminant. The aqueous solution after solubilization treatment (containing TCE and sodium dodecyl sulfate (SDS)) was used as the research object to carry out the remediation technology research of citric acid (CA) enhanced Fe(II) activation in sodium percarbonate (SPC) system. In 0.15 mM TCE and 1 critical micelle concentration (CMC) SDS solution, CA chelating Fe(II) activated SPC could effectively promote 93.2% degradation of TCE when the dosages of SPC, Fe(II) and CA were 3.0, 6.0 and 3.0 mM, respectively. SDS had a significant inhibitory effect on the degradation of TCE, and the surface tension changed after the reaction. The addition of CA greatly increased the generation of hydroxyl radicals (HO) in the system, while the removal of TCE was mainly attributed to HO, and the removed TCE was almost completely dechlorinated. The pH range from 3 to 7 could keep the TCE degradation above 80.0%. In the actual groundwater remediation, this technique could also efficiently degrade TCE (including SDS), showing a great application potential and development prospective in practice.
... Besides, natural present iron in soil can be the catalyst to activate the remedial decomposition of CP to produce free radicals as well, and no supplementary catalyst was needed [34]. There were several studies reported the application of CP in soil catalyzed with natural present catalyst [103,107]. ...
... Cool-Ox TM was further compared with modified Fenton chemistry with HP and sodium persulfate (SPS) in the treatment of PAHs contaminated soil slurry [55]. Cool-Ox TM treatment had the longest reaction time and the highest surfactant Table 9 Comparison between four oxidants used in ISCO remediation (reprinted from Ref. [52] [103,107]. Interestingly, another study showed quite opposite results that CP treatment was least effective for contaminants removal from leaking cable insulating oil-contaminated soil compared with HP and permanganate, as only 5% of the cable oil was degraded after seven days with CP treatment [109]. The discrepancy could be due to the difference in the treatment operation as CP could be self-encapsulated with the production of insoluble Ca(OH) 2 in static condition while agitation was not sufficient in the latter study. ...
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Calcium peroxide (CP) has been progressively applied in terms of environmental protection due to its certain physical and chemical properties. This review focuses on the latest progresses in the applications of CP in water and soil treatment, including wastewater treatment, surface water restoration, and groundwater and soil remediation. The stability of CP makes it an effective solid phase to supply H2O2 and O2 for aerobic biodegradation and chemical degradation of contaminants in water and soil. CP has exerted great performance in the removal of dyes, chlorinated hydrocarbons, petroleum hydrocarbons, pesticides, heavy metals and various other contaminants. The research progress in the encapsulation technologies of CP with other materials and the preparation of CP nanoparticles were also presented in this review. Based on the summarized research progresses, the perspective of CP application in the future was proposed.
... The addition of chemical or biosurfactants facilitates the transfer of contaminants from the solid to the liquid phase and improves the utilization of the oxidants to the contaminants (Fig. 9b) [146,155,156]. Moreover, Goi et al. [157] used Fe 2+ and chelated metal iron to activate persulfate in combination with biosurfactants to treat DDT-contaminated soil. They found that the addition of biosurfactants could enhance contaminants release from soil to bulk solution, to increase the degradation rate of DDT. ...
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Accumulation of multiple organic pollutants in the soil is a huge threat to ecological systems and health of human beings. Iron-based catalysts, such as zero-valent iron (ZVI) catalysts, iron oxide catalysts, and supported iron-based catalysts are widely used in sulfate radicals (SO4•−)-based advanced oxidation process (SR-AOPs) for soil remediation as a result of their environmental friendliness, extensiveness, and low cost, etc. In recent years, SR-AOPs using iron-based catalysts have arousing attention for the degradation/mineralization of organic pollutants in polluted soil. It helps to accelerate the transformation of contaminants, as well as sustainable remediation and adaptability to complex soil environments. This paper concentrates on the progresses of the Fe-based catalysts in SR-AOPs for organically contaminated soil. General persulfate activation process and the radical free radicals generation are summarized in soil remediation. The changes of physicochemical properties (e.g., organic matter, naturally occurring minerals, pH, and microbial community) in soil after SR-AOPs treatment are particularly discussed. The applications of Fe-based catalysts for SR-AOPs in soil remediation are thoroughly investigated from the perspective of the internal interaction among pollutants, catalysts, and soil. Finally, the existing challenges for SR-AOPs by Fe-based catalysts used in soil remediation are proposed.
... Based on the literature review, trichloroethene (TCE) [17,19,22], BTEX (benzene, toluene, ethylbenzene, and xylenes) [20,23,28], PAHs [13], and other refractory organic pollutants [9][10][11][12]16,[29][30][31] have been treated with the CaO 2 -based oxidation techniques. Among these pollutants, benzene is a typical one in many contaminated sites and also listed as a toxic organic compound [32,33]. ...
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This study investigated the effect of synergistic strengthening by citric acid (CA) coupled with micron zero valent iron (mZVI) in Fe(II) catalyzed sodium percarbonate (SPC) system on trichloroethylene (TCE) removal in an aqueous environment with the existence of sodium dodecyl sulfate (SDS). Compared with SPC/Fe(II), SPC/Fe(II)/mZVI, SPC/Fe(II)/CA, and SPC/Fe(II)/CA/mZVI systems, the synergistic strengthening effect by CA and mZVI could maximize TCE removal to 92.0% and dechlorination of TCE to 88.0% within 30 min. Furthermore, the synergistic system has the widest pH range of 3-7. The removal of TCE could hardly be improved by only adjusting pH in the system without CA addition, while it could be easily achieved by the synergistic strengthening SPC/Fe(II)/CA/mZVI system. Fe(II) concentration and hydroxyl radical (HO•) amount showed that the presence of CA and mZVI could continuously release Fe(II) and efficiently promote the formation of HO•. Besides HO•, reductive radicals such as superoxide radical (O2⁻•) and carbon dioxide radical (CO2⁻•) were also abundant in the SDS environment. Although the reaction kinetic constant was reduced due to the negative effects of weak alkaline pH and inorganic anions in the actual groundwater, the chemical dosages with the original ratio of SPC/Fe(II)/CA/mZVI could still reach 87.8% TCE degradation, which showed the superiority of this system for remediation of the actual contaminated groundwater.
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In situ chemical oxidation (ISCO) is a rapidly growing field for the remediation of contaminated soils and groundwater. This paper provides an overview of the four oxidation systems that are in common use for ISCO: Catalyzed H2O2 propagations (CHP) (i.e., modified Fenton's reagent), permanganate, ozone, and persulfate. Each of the oxidants has different characteristics; for example, CHP is a nonselective oxidizing and reducing system that is capable of degrading almost all organic contaminants and destroying dense nonaqueous phase liquids and sorbed contaminants, but it is unstable in the subsurface. In contrast, permanganate is a selective oxidant that reacts primarily with alkenes and is highly stable in groundwater. Ozone exhibits wide reactivity but is limited by mass transfer limitations and stability. Persulfate is the newest oxidant being used for ISCO; it is moderately stable in the subsurface, and appears to have widespread reactivity, but more research is needed on its chemistry in soils and groundwater. Although none of the ISCO reagents is ideal, these technologies have the potential to treat source zones more rapidly than other remediation processes.
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