an experimental study on the remediation of phenanthrene in soil using ultrasound and soil washing
TRANSCRIPT
ORIGINAL ARTICLE
An experimental study on the remediation of phenanthrene in soilusing ultrasound and soil washing
Weikun Song • Jianbing Li • Wen Zhang •
Xuan Hu • Ling Wang
Received: 29 November 2010 / Accepted: 30 September 2011 / Published online: 13 October 2011
� Springer-Verlag 2011
Abstract A series of laboratory experiments were carried
out in this study to investigate the remediation of phen-
anthrene contaminated soil using ultrasound and soil
washing. The results indicated that ultrasound and soil
washing could significantly enhance the remediation effi-
ciency of each other. The performance of the combined
ultrasonic and soil washing process was then investigated,
and the impacts of four experimental variables including
the initial concentration of phenanthrene in soil, sonication
time, pH of washing solution, and washing flow rate were
examined using an orthogonal experimental design
method. The analysis of variance (ANOVA) of experi-
mental results revealed that the initial phenanthrene con-
centration, sonication time and soil washing flow rate
showed significant effects (P B 0.05) on the remediation
efficiency. A pseudo-first-order kinetics model was devel-
oped for describing the remediation process, and a maxi-
mum remediation efficiency of 69.5% was observed in the
study after 20 min of treatment under the experimental
conditions. Therefore, the results indicate that the com-
bined ultrasonic and soil washing process could represent a
promising technology for the effective remediation of
phenanthrene contaminated soil.
Keywords Phenanthrene � Soil remediation �Soil washing � Ultrasound
Introduction
Phenanthrene is a common polycyclic aromatic hydrocar-
bon (PAH) originated from both natural and anthropogenic
sources. This recalcitrant chemical tends to persist in the
environment due to its low solubility and high tendency of
soil adsorption (O’Mahony et al. 2006). The contamination
of soils with phenanthrene is a challenging issue since it
poses serious risks to human and ecological health. Con-
sequently, there has been increasing research interest in its
effective remediation. During the past years, various
physical, chemical, and biological methods have been
investigated to remediate phenanthrene contaminated soils
(Isosaari et al. 2007). For example, Li et al. (2000) eval-
uated the feasibility of using a cosolvent-assisted electro-
kinetic technique for removing phenanthrene from soils,
and found that about 43% of phenanthrene was removed
after 127 days of treatment under the presence of
n-butylamine; O’Mahony et al. (2006) used ozone to
remediate phenanthrene contaminated soils, and found that
at least 50% of phenanthrene was removed from air-dried
soils after 6 h of ozone treatment, while a removal effi-
ciency of up to 85% was achieved in sandy soils; Ruberto
et al. (2006) examined the combined effects of biostimu-
lation with surfactant and bioaugmentation with PAH
degrading bacterial consortium, and found that a phenan-
threne removal of 46.6% from sandy soils was achieved
W. Song � J. Li � W. Zhang � L. Wang
MOE Key Laboratory of Regional Energy Systems
Optimization, Sino-Canada Research Academy of Energy and
Environmental Studies, North China Electric Power University,
Beijing 102206, China
J. Li (&)
Environmental Engineering Program,
University of Northern British Columbia,
Prince George, BC V2N 4Z9, Canada
e-mail: [email protected]
X. Hu
College of Environmental Sciences and Engineering,
Peking University, Beijing 100871, China
123
Environ Earth Sci (2012) 66:1487–1496
DOI 10.1007/s12665-011-1388-y
after 56 days of treatment. More recently, Zhou and Zhu
(2008) investigated the performance of applying anionic–
nonionic mixed surfactant for enhancing phenanthrene
flushing for contaminated soil, and found that up to 94% of
phenanthrene removal was obtained.
Although many previous studies have been carried out,
the strong adsorption and persistence of phenanthrene in
soil still make the remediation a very difficult task
(Isosaari et al. 2007; Villa et al. 2010). The conventional
remediation methods could hardly reach the desired pol-
lutant removal from soils (Gomez et al. 2009). For
example, as a conventional method, soil washing has
been used at contaminated sites to remove hydrocarbon
contaminants, but its effect on persistent pollutant
removal is very limited (Urum and Pekdemir 2004). In
recent years, ultrasonic technology has received increas-
ing attention as an environmentally friendly and eco-
nomically competitive approach for environmental
pollution control, including soil remediation (Shrestha
et al. 2009). Generally, the main mechanism of soil
remediation by ultrasound is to utilize physical desorp-
tion, flocculation, and chemical oxidation of pollutants
introduced by ultrasonic cavitation phenomenon (Flores
et al. 2007; Mason 2007). Ultrasound has been proved to
be effective for treating recalcitrant contaminants under
various conditions. For example, Isaza and Daugulis
(2009) examined the effects of ultrasonic irradiation on
mass transfer and degradation of PAHs by an enriched
consortium, and the results indicated that the pollutant
removal rates were improved by approximately fivefold
relative to unmixed control cases when sonication was
applied; Shrestha et al. (2009) presented a study to utilize
sonochemistry on the decontamination of hexachloro-
benzene and phenanthrene polluted soils including syn-
thetic clay, natural farm clay, and kaolin, and found that
ultrasound had a good potential to reduce the high con-
centrations of persistent organic compounds in soils.
Generally, ultrasound can be integrated with several other
treatment methods for the better treatment effect (Pham
et al. 2009). However, few studies were reported to
combine ultrasound with soil washing for the treatment of
phenanthrene contaminated soil, and more research stud-
ies are required to find cost-effective remediation methods
for such recalcitrant pollutant.
The primary objective of this study was to evaluate the
ability of combined ultrasonic and soil washing process as
a useful technique to enhance the remediation effectiveness
for treating soils contaminated with phenanthrene. The
adsorption of phenanthrene onto soil was first investigated.
An orthogonal experimental design method was then used
to examine the impacts of different factors on the reme-
diation efficiency, including the initial concentration of
phenanthrene in soils, sonication time, pH of washing
solution, and washing flow rate. The results could provide
useful information for developing environmentally friendly
methods for the cost-effective remediation of phenanthrene
contaminated soils.
Materials and methods
Contaminated soil preparation
Clean soil samples used in the experiments were collected
from North China Electric Power University campus. The
soil was air-dried and grinded using a mortar and pestle and
was screened to remove coarse particles. The grinded soils
were dried in a laboratory oven at 60�C overnight to
remove excessive moisture, and were sterilized by auto-
claving for 30 min and stored in brown glass bottles. The
properties of clean soil samples are summarized in Table 1.
Phenanthrene with a purity of greater than 98% was pur-
chased from Alfa Aesar GmbH and Co. KG. To examine
the impacts of initial soil pollutant concentration on the
remediation efficiency, three different phenanthrene con-
centrations in soil were prepared. The phenanthrene was
first dissolved in methylene chloride (CH2Cl2) using an
electrically operated mixer for about 20 min (Ahn et al.
2010), and was then added into the clean soil sample at
phenanthrene-soil mixing ratios of 0.0125, 0.025 and
0.05% (w/w), respectively. After homogeneous mixing, the
soils were placed in fume hood for 48 h to evaporate the
methylene chloride (Ahn et al. 2010). It was found from
the preliminary experiments that more than 99% of the
solvent could be evaporated after 48 h. These contaminated
soils were then stored in the fridge at 4�C. The phenan-
threne concentration in each soil sample prior to the start of
the experiments was measured using a GC/MS (Table 2).
Since the phenanthrene was also slightly evaporated, the
measured concentration was slightly lower than the theo-
retical concentration (0.0125, 0.025, 0.05%) as shown in
Table 2.
Table 1 Properties of clean soil sample
Soil size fractions (%)
Clay (\0.002 mm) 14
Silt (0.002–0.02 mm) 16
Sand (0.02–0.2 mm) 70
Textural class Sandy loam
pH 8.0
CEC (meq/100 g soil) 27.3
Organic matter (%) 2.33
1488 Environ Earth Sci (2012) 66:1487–1496
123
Soil adsorption experiments
The understanding of soil adsorption behavior is of
importance for the development of successful remediation
processes. Thus, the adsorption of phenanthrene onto soil
before remediation experiments was investigated in this
study. Fifty milliliters (mL) of phenanthrene solution was
added to a 100-mL conical beaker which contained 0.5 g of
uncontaminated soil. The soil-phenanthrene solution mix-
ture was then agitated continuously for 30 h at 25�C using
an oven controlled crystal oscillator (HZQ-C) at 140 rpm.
It was found from the preliminary experiments that the
solution mixture could reach adsorption equilibrium after
30 h. After agitation, vacuum filtration was applied for
solid/liquid separation of the mixture. The liquid sample
was transferred to a separation funnel, followed by liquid–
liquid extraction using methylene chloride as a solvent.
The adsorption experiments were conducted for a series of
solutions with different initial phenanthrene concentra-
tions. The phenanthrene adsorption (S) onto soil (mg/kg)
can then be calculated as follows (Bettahar et al. 1999):
S ¼ C0 � Cð Þ � V=M ð1Þ
where C0 is the initial phenanthrene concentration in
solution (mg/L), C is the equilibrium concentration of
phenanthrene in aqueous phase after soil adsorption (mg/L),
V is the volume of solution (mL), and M is the mass of soil
sample in the beaker (g).
Three models were used to evaluate the adsorption
behavior of phenanthrene onto soil in this study, including
linear adsorption isotherm model (Khodadoust et al. 2005),
Freundlich adsorption isotherm model (Hwang and Cut-
right 2002), and Langmuir isotherm model (Blanc et al.
2006), as described below:
S ¼ Kd � C þ b ð2Þlog S ¼ logKf þ n log C ð3Þ1
S¼ 1
Cm
þ 1
aCm
� 1
Cð4Þ
where S can be calculated using Eq. 1; Kd and Kf are
adsorption coefficients of the linear adsorption isotherm
equation and Freundlich adsorption isotherm equation,
respectively; Cm is the soil sorption capacity; b, n and s are
constants (Leglize et al. 2006; Muller et al. 2007).
Experimental procedures
Figure 1 shows the experimental setup of ultrasonic and
soil washing treatment of phenanthrene contaminated soil.
The remediation apparatus was made of a Plexiglas cyl-
inder with an inside diameter of 40 mm and a total length
of 160 mm. It consists of an influent chamber, a reaction
chamber and an effluent chamber. The phenanthrene con-
taminated soil was placed in the reaction chamber. The
120-mesh stainless steel woven wire screens were placed
between the reaction chamber and the other two chambers
to prevent soil loss during washing treatment. Deionized
water was added to the influent reservoir as the washing
solution, and its pH was regulated with H2SO4 or NaOH
solution. The ultrasonic processor used in this study was a
Misonix Sonicator 3000 which consists of a generator, a
converter and a standard acoustic horn. The generator
could convert conventional 50/60 Hz alternating current at
110 V to a 20 kHz electrical energy. There was a hole with
a diameter of 20 mm on the top of the reaction chamber.
Before experiment, 10 g of phenanthrene contaminated
soil sample was carefully placed in the reaction chamber,
and the 12-mm diameter titanium sonic probe was inserted
Table 2 Phenanthrene concentration in soil
Phenanthrene-soil mixing
ratio (%)
Measured phenanthrene concentration in
soil (mg/kg)
0.0125 101.04
0.025 223.33
0.05 454.58
Converter
AcousticHorn
ReactionChamber
InfluentReservoir
PeristalticPump
EffluentReservoir
Stainless Screen(120mesh)
UltrasonicGenerator
Fig. 1 Sketch of ultrasonic and
soil washing experimental setup
Environ Earth Sci (2012) 66:1487–1496 1489
123
through the hole into the center of the soil sample and was
then fixed. The soil sample was saturated with the solution
pumped from the influent reservoir, and once the water
level was maintained at about 1 cm above the soil sample,
the remediation experiment was initiated. The experimen-
tal setup could allow for different experiments, including
soil washing alone, ultrasonic treatment alone, and com-
bined ultrasonic and soil washing. For combined ultrasonic
and soil washing treatment, the soil sample was applied
with the ultrasonic energy at 20 kHz frequency, and at the
same time the washing solution was pumped from the
influent reservoir into the reactor. The contaminants from
the reaction chamber were carried by the solution which
was eventually collected with the effluent reservoir. For
soil washing alone treatment, ultrasonic energy was not
applied, and for ultrasonic treatment alone, soil washing
was not applied. After a given period of remediation
treatment, the soil sample was taken out of the reaction
chamber and sent for GC/MS analysis of phenanthrene.
In this study, all the experimental procedures were
completed carefully with clean equipment. The decon-
tamination of glassware and other materials was completed
by washing with surfactant, Alconox, and hot water fol-
lowed by a deionized water rinse. The experimental
materials were tested for extractable concentrations of
phenanthrene, and none of the materials contained phen-
anthrene. Each experimental run had three replicates. After
every replicate of experiment, a method blank using
uncontaminated soil sample was run through the treatment
system and then the sample was analyzed to test the con-
tamination of sample by residual phenanthrene in the
experimental apparatus. Furthermore, a lab blank consist-
ing of a blank GC vial of solvent was analyzed for each
replicate to test for contamination from the analytical
apparatus (GC–MS). The removal efficiency (RE) of
phenanthrene in soil after remediation was calculated as
follows:
RE %ð Þ ¼ Ci � Crð Þ=Ci½ � � 100% ð5Þ
where Ci is the initial concentration of phenanthrene in soil
before remediation and Cr is phenanthrene concentration in
soil after remediation.
GC/MS analysis of phenanthrene
The soil sample in the reaction chamber was collected after
each remediation experiment and sent for liquid–solid
extraction using mechanical shaking method (Siddique
et al. 2006). Methylene chloride was used as the solvent
extractant and the extracted sample passed through a silica
gel column cleanup procedure. The extract volume after
silica gel column cleanup was reduced using a rotary
evaporator to \2 mL. The sample was then brought up to
2.0 mL with n-hexane and transferred into a GC vial by
using a glass needle tube and pipette. The GC/MS analysis
was conducted using Agilent 5975C MSD and 7890GC
equipped with a HP-5MS capillary column (length of
30 m, I. D. of 0.25 mm, and film thickness of 0.25 lm).
The carrier gas was helium with a flow rate of 1 mL/min
and the pre-column pressure was 0.03 MPa; the sample
injection volume was 1 lL with automatic injection and
without split. The initial oven temperature was 40�C, and
was increased to 260�C at a rate of 5�C/min and then
maintained for 20 min. The mass spectrum conditions were
electron impact ionization, electron energy of 70 eV, scan
range of 45–600 amu, temperature of ion source at 230�C,
and temperature of quadrupoles at 150�C. The concentra-
tion of phenanthrene was quantified using external standard
method.
Orthogonal experimental design of soil remediation
Orthogonal experimental design method was used to
investigate the effect of four factors on the remediation
efficiency when using combined ultrasonic and soil wash-
ing process. As compared to the single-factor experiment,
orthogonal method can more efficiently and precisely
extract experimental information and require less number
of experimental tests (Jiang and Komanduri 1997). The
investigated factors include the initial concentration of
phenanthrene in soil (factor A), sonication time (factor B),
pH of solution (factor C), and soil washing flow rate (factor
D). Each factor was examined with three levels. The
phenanthrene-soil mixing ratio was used to represent the
initial phenanthrene concentration in soil and its three
levels (A1, A2, A3) were 0.0125, 0.025, and 0.05%,
respectively. The three levels were 1, 5, and 10 min (B1,
B2, B3) for sonication time, and 2.0, 7.0, and 12.0 (C1, C2,
C3) for solution pH. As for soil washing flow rate, its three
levels (D1, D2, D3) were 0, 0.2, and 0. 4 L/min, respec-
tively. Table 3 lists the combination of factor levels of the
orthogonal experimental design. Statistical analyses were
then conducted to examine the validity of experiments.
Results and discussion
Determination of adsorption isotherm
From the soil adsorption experimental results (Fig. 2), it
was found that the linear model and Freundlich model
obtained better fit with high correlation coefficients. The
large Kd value (220.26 L/kg) of phenanthrene in the linear
adsorption isotherm implied the low solubility of phenan-
threne which could result in difficulties for remediation by
a conventional method such as using soil washing alone
1490 Environ Earth Sci (2012) 66:1487–1496
123
(Zhao et al. 2001). On the other hand, the relatively high
values of n (1.73) and Kf (130.47) in the Freundlich
adsorption isotherm indicate that the soil sample had a high
adsorption capacity even at a lower equilibrium concen-
tration (Zeng et al. 2006). As a result, the effective
desorption of phenanthrene from contaminated soil, which
could be achieved by ultrasonic treatment, is important for
its successful remediation.
Impact of ultrasound on soil washing treatment
A series of experiments with ultrasonic power changing
from 0 to 96 W were conducted to examine the impacts of
ultrasound on soil washing for the remediation of phen-
anthrene, and the results are presented in Fig. 3. It can be
observed that ultrasound had an obvious positive effect on
the removal of phenanthrene from soil when using soil
washing. When ultrasonic power was zero, soil washing
can hardly remove phenanthrene from the contaminated
soil, mainly due to the low solubility of phenanthrene in
water implied by large Kd value. However, when ultrasonic
power was applied, the removal efficiency of phenanthrene
increased significantly. For example, the removal effi-
ciency was 35.1% when ultrasonic power was 24 W as
compared to nearly zero pollutant removal with soil
washing alone. Further increase of ultrasonic power from
24 to 96 W resulted in slight increase of phenanthrene
removal efficiency, while a removal efficiency of 55.6%
was observed when ultrasonic power was 96 W. Generally,
increasing ultrasonic power could improve the shear force
of soil particle surface and increase the desorption of
organic pollutants from soil particles. The increase of
phenanthrene desorption is of critical importance for its
effective remediation due to the high adsorption capacity
implied by large n and Kf values. Increasing ultrasonic
power can also increase energy input to the soil/water/
pollutant reaction system, thus improving ultrasonic cavi-
tation effect and increasing the removal efficiency of
organic compounds (Suslick et al. 1990; Mason 2007).
Orthogonal experiments on combined ultrasonic
and soil washing treatment
As described above, ultrasound showed a very positive
effect on promoting the removal of phenanthrene from
contaminated soil when using soil washing method. As a
result, a series of experiments based on orthogonal design
method were conducted to further investigate the impacts
of various experimental variables on phenanthrene reme-
diation efficiency when using the combined ultrasonic and
soil washing remediation. The experimental design was
presented in Table 3, while the ultrasonic power applied in
the experiments was 42 W. The phenanthrene concentra-
tions in soil samples before and after ultrasonic treatment
Table 3 Orthogonal experimental design
Test
number
Combination of factor value for each experimental test
Phenanthrene-
soil mixing
ratio (A)
Sonication
time (min)
(B)
pH of
washing
solution (C)
Washing
flow rate
(L/min) (D)
1 0.0125% (A1) 1 (B1) 2.0 (C1) 0 (D1)
2 0.0125% (A1) 5 (B2) 7.0 (C2) 0.2 (D2)
3 0.0125% (A1) 10 (B3) 12.0 (C3) 0.4 (D3)
4 0.025% (A2) 1 (B1) 7.0 (C2) 0.4 (D3)
5 0.025% (A2) 5 (B2) 12.0 (C3) 0 (D1)
6 0.025% (A2) 10 (B3) 2.0 (C1) 0.2 (D2)
7 0.05% (A3) 1 (B1) 12.0 (C3) 0.2 (D2)
8 0.05% (A3) 5 (B2) 2.0 (C1) 0.4 (D3)
9 0.05% (A3) 10 (B3) 7.0 (C2) 0 (D1)
0
50
100
150
200
250
300
350
Con
cent
ratio
n in
soi
l(mg/
kg)
Concentration in the aqueous phase(mg/L)
y = 220.2631x - 75.9861 R2 = 0.9977
(a)
0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
-0.4 -0.3 -0.2 -0.1 0.0 0.1 0.2 0.31.4
1.6
1.8
2.0
2.2
2.4
2.6
Log 10
S
Log10
C
y = 1.7299x + 2.1155 R2 = 0.9883
(b)
Fig. 2 Adsorption isotherm of phenanthrene onto soil. a linear
adsorption isotherm equation, b Freundlich adsorption isotherm
equation
Environ Earth Sci (2012) 66:1487–1496 1491
123
are shown in Fig. 4, while the experimental conditions for
different tests are listed in Table 3. It is found that phen-
anthrene concentrations in the soil samples were reduced
after remediation treatment, with removal efficiencies
ranging from 5.77 to 40.83% under different experimental
conditions.
Identification of major factors
To explore the impact of each experimental variable, it is
necessary to use the analysis of variance (ANOVA) method
to analyze the experimental data. In this study, ANOVA
was conducted using the SPSS 13.0 package. The removal
efficiency of phenanthrene was selected as the response
variable, while the initial phenanthrene concentration in
soil, sonication time, solution pH, and washing flow rate
were selected as the fixed factors. The significance level (a)
for the analysis was set at 0.05 and P value results of\0.05
(P B 0.05) from ANOVA were considered statistically
significant. The ANOVA results are presented in Table 4.
It was found that three variables (initial phenanthrene
concentration, sonication time, and soil washing flow rate)
showed significant effects (P B 0.05) on the variation in
phenanthrene removal efficiency when using combined
ultrasonic and soil washing process, except for pH
(P [ 0.05). The influence order of experimental factors on
phenanthrene removal efficiency was sonication time [initial concentration [ washing flow rate. To examine the
influence of each major factor on the performance of the
combined remediation process, the signal to noise (S/N)
analysis of orthogonal experiments was conducted (Fig. 5).
The S/N ratio was evaluated using the following equation
(Ross 1996):
S/N ¼ �10 logXn
i¼1
1
y2i
� �=n ð6Þ
where S/N denotes the performance statistic for the treat-
ment, yi denotes the observed data, n is the number of
observations. The unit of S/N ratio is decibels (dB). The
higher the S/N ratio, the better the result is (Taguchi et al.
2005).
Influence of sonication time
It is found that the S/N value of sonication time (factor B)
from level 1 to level 3 was 53.84, 73.20 and 80.38,
respectively, and the variation of S/N values for this factor
due to factor level change was the largest among all the
investigated factors (Fig. 5). This indicates that sonication
time was the most significant factor affecting the perfor-
mance of the combined remediation process. The change of
S/N value (from 53.48 to 73.20) when changing sonication
time from level 1 (1 min of sonication) to level 2 (5 min of
sonication) was more significant than that when changing
sonication time from level 2 to level 3 (10 min of sonica-
tion). This indicates that within the first 5 min increasing
sonication time significantly improves the removal effi-
ciency of phenanthrene. The removal efficiency is less
significant at longer duration of ultrasonic treatment
(5–10 min). Initially, the phenanthrene molecules farther
away from the soil particle surface with weak bonding
force could be easily removed, but as time went on, the
phenanthrene molecules adsorbed at the inner layers could
hardly be removed due to stronger bonding force.
0 12 24 36 48 60 72 84 96 1080
10
20
30
40
50
60
Rem
oval
rat
e(%
)
Ultrasonic power(W)
Fig. 3 Impact of ultrasound on the removal efficiency of phenan-
threne when using soil washing (experimental conditions: phenan-
threne-soil mixing ratio of 0.05%, 10 min ofsonication time, and
0.4 L/min of soil washing flow rate)
0 1 2 3 4 5 6 7 8 9 100
100
200
300
400
500
Phe
nant
hren
e co
ncen
trat
ion(
mg/
kg)
Test number
initial final
Fig. 4 Phenanthrene concentrations in soil before and after ultrasonic
treatment under different experimental conditions
1492 Environ Earth Sci (2012) 66:1487–1496
123
A series of experiments were designed to further
investigate the impacts of sonication time on phenanthrene
removal (Fig. 6). It was observed that ultrasound could
significantly promote the reduction of phenanthrene in soil
during the first 20 min of treatment. For example, after
1 min of treatment, the pollutant removal increased from
nearly 0 to 17.7%. The phenanthrene removal then
increased to 43.3 and 55.5% after 5 and 10 min of treat-
ment, respectively. But after 20 min of treatment, the
removal efficiency of phenanthrene leveled off at around
69.5%, which indicated that the residual phenanthrene in
soil was difficult to be removed due to strong bonding
force.
Influence of initial concentration of phenanthrene in soil
The initial concentration of phenanthrene in soil (factor A)
had a significant influence on phenanthrene removal effi-
ciency (Fig. 5). When factor A increased from level 1
(101.04 mg/kg) to level 2 (223.33 mg/kg), the value of S/N
increased significantly from 62.78 to 72.62. While the
initial concentration of phenanthrene increased from level
2 to level 3 (454.58 mg/kg), the S/N curve almost leveled
off (from 72.62 to 72.02). This can also be observed in
Fig. 4, when the initial concentration was increased from
level 1 to level 2, the phenanthrene reduction was increased
significantly. At low phenanthrene concentration, strong
bonding force makes phenanthrene molecules adsorb to
soil particles surface as monolayer, and only higher energy
of desorption can break down the bonding between them.
At high phenanthrene concentration in soil, phenanthrene
molecules adsorb to soil particles surface as multilayers
and the bonding force was weak so that phenanthrene
molecules on the outside layers can be easily desorbed by
ultrasonic cavitation. Thus, the higher the phenanthrene
Table 4 ANOVA results of orthogonal experiments
Source Type III sum of squares df Mean square F Sig. (P)
Corrected model 2,675.397a 10 267.540 9.680 0.000
Intercept 16,139.883 1 16,139.883 583.989 0.000
Initial concentration 372.841 2 186.421 6.745 0.008
Sonication time 1,964.961 2 982.481 35.549 0.000
pH of solution 63.330 2 31.665 1.146 0.343
Washing flow rate 245.010 2 122.505 4.433 0.029
Repeat group 29.255 2 14.627 0.529 0.599
Error 442.197 16 27.637
Total 19,257.477 27
Corrected total 3,117.594 26
a R2 = 0.858 (adjusted R2 = 0.770)
A1 A2 A3 B1 B2 B3 C1 C2 C3 D1 D2 D345
50
55
60
65
70
75
80
85
S/N
= -
10lo
g(su
m(1
/y2)/
n)
Factor and level
Fig. 5 Effects of experimental factors on the removal efficiency of
phenanthrene
0 5 10 15 20 25 300
10
20
30
40
50
60
70
80
Rem
oval
rat
e(%
)
Sonication time(min)
Fig. 6 Variation of phenanthrene removal efficiency with sonication
time for combined soil washing and ultrasonic remediation (exper-
imental conditions: phenanthrene-soil mixingratio of 0.05%, 96 W of
ultrasonic power, and 0.4 L/min of washing flow rate)
Environ Earth Sci (2012) 66:1487–1496 1493
123
concentration was, the higher the removal efficiency of
phenanthrene was. This is in agreement with previous
studies, for example, Feng and Aldrich (2000) indicated
that when the diesel content of soil was raised from 0.5 to
5%, the removal efficiency of sonochemical treatment of
soil was increased from 77% to around 91%.
Influence of soil washing flow rate
It was also found that the S/N value of washing flow rate
(factor D) from level 1 to level 3 was 63.82, 70.67 and
72.94, respectively (Fig. 5). The increase of washing flow
rate from level 1 to level 3 led to considerable increase of
S/N value. The difference of S/N between with soil
washing (level 2) and without soil washing (level 1) was
obvious since water flow would increase contaminant
transport and decrease phenanthrene re-adsorption during
the combined treatment process. When washing flow rate
was slow (level 2), the time-dependent process of the
breakdown of contaminant/soil bonding allowed for more
interaction of contaminant/soil system, and this would
release the contaminants trapped in the soil pore space and
adsorbed on the soil particle surfaces to the aqueous phase.
However, increasing washing flow rate from level 2 to
level 3 led to less increase of S/N value and thus less
increase of phenanthrene removal efficiency. This might be
due to insufficient contact time for contaminant/soil bond
to be broken when water flow was too fast.
A series of experiments were carried out to further
investigate the impacts of soil washing on phenanthrene
removal when using ultrasound (Fig. 7). For these experi-
ments, when ultrasound was applied alone without soil
washing, phenanthrene removal was 31.5%. It was
observed that phenanthrene removal rate was increased
from 31.5 to 55.6% when the soil washing flow rate was
increased from 0 to 0.5 L/min. The efficiency was
increased to about 42.3% when soil washing was applied
with a flow rate of 0.1 L/min. When the washing flow rate
was increased to 0.2 L/min, phenanthrene removal was
increased to 48.2%. Thus, soil washing could significantly
improve the ultrasonic remediation efficiency. The increase
of phenanthrene removal was fast when washing flow rate
was below 0.4 L/min, but the efficiency nearly leveled off
at 55.6% when the flow rate was above 0.4 L/min (Fig. 7).
Further increase of soil washing flow rate did not lead to
further increase of pollutant removal.
Phenanthrene removal kinetics for the combined
remediation process
As described above, the sonication time was found as the
most important factor affecting the combined remediation
process for phenanthrene removal. A pseudo-first-order
kinetics model was then assumed as follows to describe the
removal of phenanthrene from soil:
� lnðCt=C0Þ ¼ kt þ d ð7Þ
where C0 and Ct are the phenanthrene concentrations in
soil at time zero and t (min) after remediation treatment,
respectively; k is a pseudo-first-order rate constant (in
min-1), and d is a constant. The experimental results
obtained from the investigation of the impacts of sonication
time on phenanthrene removal as described above were
used for developing the kinetics model (Fig. 8). The
0.0 0.1 0.2 0.3 0.4 0.50
10
20
30
40
50
60
Rem
oval
rat
e(%
)
Flow rate(L/min)
Fig. 7 Effects of soil washing on the removal efficiency of phenan-
threne when using ultrasound (experimental conditions: phenan-
threne-soil mixing ratio of 0.05%, 10 min ofsonication time, and 96 W
of ultrasonic power)
0 5 10 15 20
0.0
0.2
0.4
0.6
0.8
1.0
1.2
y = 0.0570x + 0.1448
R2 = 0.9188
-LN(C
t/C
0)
Sonication time(min)
Fig. 8 Change of phenanthrene concentration in soil for the
combined soil washing and ultrasonic process (experimental condi-
tions: phenanthrene-soil mixing ratio of 0.05%, 96W of ultrasonic
power, and 0.4 L/min of washing flow rate)
1494 Environ Earth Sci (2012) 66:1487–1496
123
correlation coefficient (R2) was 0.9188, indicating that the
pseudo-first-order kinetics model could well describe the
remediation of phenanthrene in soil using combined
ultrasonic and soil washing process. The rate constant
k was found to be 0.057 min-1, which implies that the
process had significant accelerating effect on the removal
of phenanthrene in soil, and a high removal efficiency of
the recalcitrant phenanthrene can be achieved within a very
short treatment time. This is due to the fact that soil
washing and ultrasonic remediation could enhance the
performance of each other. Ultrasonic cavitation could
effectively promote the desorption of phenanthrene from
soil even though it had high adsorption capacity.
Conclusions
The effect of ultrasound and soil washing on the remediation
of phenanthrene contaminated soil was investigated in this
study, and a series of orthogonal experiments were designed
and implemented. The impacts of four experimental vari-
ables on phenanthrene removal were examined for the
combined ultrasonic and soil washing process. The analysis
of variance (ANOVA) results of the orthogonal experiments
indicated that the initial concentration of phenanthrene,
sonication time and washing flow rate had significant effect
(P B 0.05) on soil phenanthrene removal. The signal to
noise (S/N) analysis illustrated that the increase of initial
concentration of phenanthrene, sonication time and washing
flow rate can improve pollutant removal efficiency in
varying degrees. A pseudo-first-order kinetics model was
developed to describe the remediation of phenanthrene in
soil, and the rate constant k was found to be 0.057 min-1,
implying that a high removal efficiency of phenanthrene can
be achieved within a short-treatment period. The results
revealed that after 20 min of ultrasonic treatment, the
removal efficiency of phenanthrene reached its maximum
capacity (69.5%) under the experimental conditions. Con-
sequently, the combination of ultrasound and soil washing
could represent a promising technology for the remediation
of soil contaminated with recalcitrant phenanthrene.
Acknowledgments This study has been supported by the Natural
Science and Engineering Research Council of Canada and Beijing
Natural Science Foundation (No. 8102032). The authors would like to
thank the anonymous reviewers for their comments and suggestions
that helped in improving the manuscript.
References
Ahn CK, Woo SH, Park JM (2010) Surface solubilization of
phenanthrene by surfactant sorbed on soils with different organic
matter contents. J Hazard Mater 177(1–3):799–806
Bettahar M, Schafer G, Baviere M (1999) An optimized surfactant
formulation for the remediation of diesel oil polluted sandy
aquifers. Environ Sci Technol 33(8):1273–1286
Blanc P, Saada A, Baranger P (2006) A nonlinear parametric model
for phenanthrene sorption. J Colloid Interf Sci 299(1):14–21
Feng D, Aldrich C (2000) Sonochemical treatment of simulated soil
contaminated with diesel. Adv Environ Res 4:103–112
Flores R, Blass G, Dominguez V (2007) Soil remediation by an
advanced oxidative method assisted with ultrasonic energy.
J Hazard Mater 140(1–2):399–402
Gomez J, Alcantara MT, Pazos M, Sanroman MA (2009) A two-stage
process using electrokinetic remediation and electrochemical
degradation for treating benzo[a]pyrene spiked kaolin. Chemo-
sphere 74(11):1516–1521
Hwang SC, Cutright TJ (2002) Biodegradability of aged pyrene and
phenanthrene in a natural soil. Chemosphere 47(9):891–899
Isaza PA, Daugulis AJ (2009) Ultrasonically enhanced delivery and
degradation of PAHs in a polymer–liquid partitioning system by
a microbial consortium. Biotechnol Bioeng 104(1):91–101
Isosaari P, Piskonen R, Ojala P, Voipio S, Eilola K, Lehmus E,
Itavaara M (2007) Integration of electrokinetics and chemical
oxidation for the remediation of creosote-contaminated clay.
J Hazard Mater 144(1–2):538–548
Jiang M, Komanduri R (1997) Application of Taguchi method for
optimization of finishing conditions in magnetic float polishing
(MFP). Wear 213(1–2):59–71
Khodadoust AP, Lei L, Antia JE, Bagchi R, Suidan MT, Tabak HH
(2005) Adsorption of polycyclic aromatic hydrocarbons in aged
harbor sediments. J Environ Eng 131(3):403–409
Leglize P, Saada A, Berthelin J, Leyval C (2006) Evaluation of
matrices for the sorption and biodegradation of phenanthrene.
Water Resour 40(12):2397–2404
Li A, Cheung KA, Reddy KR (2000) Cosolvent-enhanced electroki-
netic remediation of soils contaminated with Phenanthrene.
J Environ Eng 126(6):527–533
Mason TJ (2007) Sonochemistry and the environment–providing a
‘‘green’’ link between chemistry, physics and engineering.
Ultrason Sonochem 14(4):476–483
Muller S, Totsche KU, Kogel-Knabner I (2007) Sorption of polycy-
clic aromatic hydrocarbons to mineral surfaces. Eur J Soil Sci
58(4):918–993
O’Mahony MM, Dobson ADW, Barnes JD, Singleton I (2006) The
use of ozone in the remediation of polycyclic aromatic
hydrocarbon contaminated soil. Chemosphere 63(2):307–314
Pham TD, Shrestha RA, Virkutyte J, Sillanpaa M (2009) Recent
studies in environmental applications of ultrasound. Can J Civil
Eng 36(11):1849–1858
Ross PJ (1996) Taguchi Techniques for Quality Engineering.
McGaw-Hill, New York
Ruberto LAM, Vazquez SC, Curtosi A, Mestre MC, Pelletier E, Mac
Cormack WP (2006) Phenanthrene biodegradation in soils using
an Antarctic bacterial consortium. Biorem J 10(4):191–201
Shrestha RA, Pham TD, Sillanpaa M (2009) Effect of ultrasound on
removal of persistent organic pollutants (POPs) from different
types of soils. J Hazard Mater 170(2–3):871–875
Siddique T, Rutherford PM, Arocena JM, Thring RW (2006) A
proposed method for rapid and economical extraction of
petroleum hydrocarbons from contaminated soils. Can J Soil
Sci 86(4):725–728
Suslick KS, Doktyes SJ, Flint EB (1990) On the origin of
sonoluminescence and sonochemistry. Ultrasonics 28(5):
280–290
Taguchi G, Chowdhury S, Wu Y (2005) Taguchi’s quality engineer-
ing handbook. Wiley, Hoboken
Urum K, Pekdemir T (2004) Evaluation of biosurfactants for crude oil
contaminated soil washing. Chemosphere 57(9):1139–1150
Environ Earth Sci (2012) 66:1487–1496 1495
123
Villa RD, Trovo AG, Nogueira RFP (2010) Soil remediation using a
coupled process: soil washing with surfactant followed by photo-
Fenton oxidation. J Hazard Mater 174(1–3):770–775
Zeng GM, Zhang C, Huang G, Yu J, Wang Q, Li JB, Xi B, Liu H
(2006) Adsorption behavior of bisphenol A on sediments in
Xiangjiang River, Central-south China. Chemosphere 65(9):
1490–1499
Zhao XK, Yang GP, Wu P, Li NH (2001) Study on adsorption of
chlorobenzene on marine sediment. J Colloid Interf Sci
243(2):273–279
Zhou W, Zhu L (2008) Enhanced soil flushing of phenanthrene by
anionic-nonionic mixed surfactant. Water Res 42(1–2):101–108
1496 Environ Earth Sci (2012) 66:1487–1496
123