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REV. CHIM. (Bucharest) ♦ 65♦ No.1 ♦ 2014http://www.revistadechimie.ro44
Different Methods for Polychlorinated Biphenyls Removal
from Contaminated Soils
DIANA MARIANA COCARTA, IRINA AURA ISTRATE*, CORA BULMAU, RAMONA DINU, VLADIMIR TANASIEV,
CRISTINA DUMITRESCU
University Politehnica of Bucharest, Faculty of Power Engineering, Department of Energy Production and Use, 313 Splaiul
Independentei, 060042, Bucharest, Romania
The paper presents results of laboratory experiments focused on the efficiency of polychlorinated biphenyls
(PCBs) removal by electroremediation, pyrolysis and incineration decontamination methods. The experiments
were carried out using soil contaminated with heavy metals and PCBs. Different process parameters were
changed during the experiments in order to achieve maximum removal efficiency. Concerning the thermal
methods (pyrolysis and incineration), the operating temperature and retention time were the two key
parameters affecting the processes that were assessed. With regards to the electroremediation alternative
for soil decontamination, the redox potential (ORP), pH, electric field and temperature were continuously
monitored. Results showed that thermal treatments are the most indicated methods for removing PCBs
from contaminated soils. Pyrolysis and incineration remediation methods ensured, with some exceptions,
an efficiency of over 99%. The same efficiency level was attended just in case of applying the electrochemical
method for removing PCB126.
Keywords: soil pollution, polychlorinated biphenyls, incineration, pyrolysis, electrokinetic remediation
The importance of soil on human life has always been
recognized but the anthropogenic activities have often had
a negative impact on the quality of the soil. Different types
of organic and/or inorganic pollutants were shown to
contaminate important surfaces. PCBs are one of the most
dangerous pollutants for both human health and the
environment. PCBs are a family of man-made chemicals
that contain 209 individual compounds with various toxicity
levels and have been widely used as coolants and lubricants
in capacitors and other electrical equipment because of
their insulating and non-flammable properties [1, 2].
Actually, at European level, waste-containing PCBs are
carefully monitored and specific regulations are applied.
Worldwide, much effort is invested in developing or
improving new remediation methods or principles ensuring
fast and improved remediation of contaminated soils.
Different methods, such as thermal, chemical, microbial
or physicochemical, are used alone or in various
combinations, i.e. in situ, on site or off site applications [3]
for the remediation of contaminated soils. In this context,
the authors of this paper compared three types of soil
decontamination technologies. Concerning the thermal
treatments, the degrees of PCBs soil remediation and PCBs
emission levels (for pyrolysis and incineration cases) have
been assessed. The behavior of PCB28, PCB77, PCB126,
and PCBs has been studied by applying different process
parameters. During the incineration, three process
temperatures have been considered: 600, 800 and 1000°C.
Throughout the pyrolysis process, the applied process
temperatures were: 400, 600 and 800°C. For both thermal
treatment methodologies, two retention times of the solid
material within the incineration and respectively, pyrolysis
reactor were taken into account: 30 and 60 min. Related
to the electrochemical remediation of soil contaminated
with PCBs, the experimental tests monitored the
parameters with high influence on the process efficiency:
specific voltage (1V/cm), current density, ORP, time and
soil pH.
* email: ia_istrate@yahoo.com; Tel.: +40.723.542.609
Experimetal part
Materials and methods
Soil samples description and analysis method
The soil used during the experimental campaign was
collected from one of the most contaminated areas within
Central Romania. The soil was historically contaminated
with heavy metals (Pb, Cd, Ni, As, Zn, Cu, Fe, Mn, Cr, Co, Hg,
As and Be) and artificially contaminated, only for laboratory
purposes, with transformer oil. In this way, soil polluted
with PCBs has been ensured with an initial concentration
for PCBs of 4.4661 mg/kgdw. According to the national
legislation, Order 756/1997, the intervention threshold for
sensible use is established at 1 mg/kgdw. So, the initial
concentration for PCBs has exceeded four times the legal
limit. Table 1 shows the main composition of the
contaminated soil before decontamination (where PAL
mobile phosphorus content [mg/kg]; KAL is potassium
content [mg/kg]; Nt is total nitrogen [%]). The main
characteristics of the contaminated soil are: apparent
density is 1.2 g/cm3, while soil humidity is 20%; from the
granulometry analysis it could be noticed that more than
Table 1
RAW SOIL COMPOSITION AND HEAVY METALS AND PCBs
CONCENTRATION LEVELS
REV. CHIM. (Bucharest) ♦ 65 ♦ No. 1 ♦ 2014 http://www.revistadechimie.ro 45
55% was composed by particle with a diameter smaller
than 0.08 mm.
In order to identify the PCBs concentration levels in the
soil, the following standards were applied: EN 10382:2007,
SR EN 15308:2008; EPA Method 3540. The analysis method
has been used both for contaminated and decontaminated
soil samples, before and after the decontamination
treatment. Before weighing, the solid material was sieved
using a 10-mesh sieve and approximately 2-mm openings
in thickness. The material was first weighed, mixed with
sodium sulphate as drying agent and then sieved. The
purpose of using this chemical substance was to provide a
uniform drying of the sample particles surface. Following
that, applying the Soxhlet extraction the solid samples were
brought to a form that allowed for their analysis. About 20g
of dried solid material were mixed with 250 mL of HPLC
grade petroleum ether solvent. The extract was
concentrated to a low solvent volume using a Heidolph
rotary evaporator and was re-eluted with hexane. A gas
chromatograph with a Shimadzu QP2010 type mass
detector has been used to quantify the PCBs concentrations
within the soil sample. Calibration curves were obtained
using a series of standard solutions, prepared by diluting
the standard mix (Pesticide Mix 20 from Dr. Ehrenstorfer)
to the desired concentrations using hexane (EPA Method
3540).
Experimental part
Thermal treatment plant
Both thermal treatments (incineration and pyrolysis)
have been carried out using the same experimental facility.
The compact batch facility is presented in figure 1.
The experimental facility consists of a unique stainless
steel horizontal reactor, externally heated by a series of
inductive electrical resistances. The reactor has an external
diameter of about 60 mm and a total capacity of 800 g of
solid material. Due to the appropriate position of the
electrical resistances, the uniformity of the temperature
field inside the pyrolysis/incineration reactor is guaranteed.
The furnace is equipped with automatic and integrated
control and can be heated over a length of maximum 750
mm. The maximum achievable temperature is 1300°C
using the multi-stage time-temperature settings. 4 kW is
the power consumed at a nominal rate. Two ceramic
fibreboards externally insulate the furnace with positive
impact on external surface heat losses. As already stated,
the facility can be used both for pyrolysis or incineration
processes based on the gaseous fluid introduced in the
reactor (nitrogen or air). The solid material is manually
loaded into the reactor. In order to determine the existence
of PCBs within the flue gas stream, a portable sampling
device form TECORA-Isostack Basic has been used. The
system allowed the capitation of both solid and gaseous
PCBs within the gas stream. The measurement method of
this device is based on isokinetic sampling conditions of a
gas volume and deposition of toxic substances on PUF
and quartz filter element, correspondingly to EN1948 [4].
Electrochemical treatment
Another treatment methodology applied during the
present research was the electrochemical one. This
method involved the use of an electric current in order to
create an electric field in the polluted area by using
electrodes placed into the ground. So, the electric based
treatment, also known as electrochemical treatment, uses
a specific DC electrical signal to mineralize organic
compounds. Specific DC converters produce a low-voltage,
low-amperage electric field that polarizes the soil or
sediments, so that the soil particles charge and discharge
electricity. This causes redox reactions that occur at all
interfaces within the soil – water – contaminant – electrode
system, mineralizing organics. Electric fields, as well as
electron transfer processes, have been used for the
decontamination of soils and underground water containing
unwanted organic or inorganic substances. The main
phenomena involved in the experimental tests were:
electrolysis, electrophoresis, electro osmosis, and electro
migration. When suitable anodes and cathodes are
strategically buried in the ground or placed in contact with
slurry and an electric field from a DC source is applied, one
or more of these phenomena occur and the output effect
is used for the removal of polluting substances. Tests were
performed using electrochemical remediation; pilot plant
equipment was developed in the framework of
RECOLAND project and entitled IPER 2 (fig. 2).
Fig.1. Thermal treatment
experimental facility
Fig. 2. Experimental setup
IPER 2 – electrochemical
cell, power supply and the
sensors used for pH and
redox measurements
REV. CHIM. (Bucharest) ♦ 65♦ No.1 ♦ 2014http://www.revistadechimie.ro46
Results and discussions
Pyrolysis of the artificially contaminated samples
Soil used during the experimental campaigns has the
same characteristics as illustrated in table 1. For every
single test, a sample of contaminated soil with PCBs was
used. The results of the pyrolysis process showed PCBs
removal efficiency from soil between 97% and 99% as a
consequence of process temperatures (400, 600°C and
800°C) and different retention times of the solid material
inside the reactor (30 min and, respectively 60 minutes).
Figures 3.a and 3.b illustrate removal efficiencies for every
single contaminant (PCB28, PCB77 and PCB126), but also
for PCBs.
Concerning PCB28, except the case of 400°C pyrolysis
temperature and 30 min retention time for which the
removal efficiency is of 96.38%, all other experiments
revealed efficiencies of more than 99% for PCB28.
Furthermore, no major difference can be noticed between
the lowest and the highest values of the PCB28 removal
efficiencies: a lesser amount than 1%. This is valid for both
retention times during soil pyrolization. For a process
temperature of 400°C, the influence of the retention time
is higher: increasing the retention time from 30 to 60 min
lead to the increase with 2.94% of the PCB28 elimination
efficiency. The highest PCB28 removal efficiency was of
more than 99.949% at a retention time of 60 min and 600°C
process temperature. If in terms of the 400°C process
temperature, the retention time has no influence on the
PCB28 removal efficiency, the same situation does not
apply in terms of soil pyrolysis at 600°C (fig. 4 and fig. 5).
Due to the fact that PCB28 and PCBs concentration
levels in soil are regulated by the Romanian MWFEP Order
no. 756/1997, the levels of PCB28 and PCBs from pyrolized
soil were compared with the national reference levels. In
this case, for both alert and intervention levels for less
sensitive use (industrial), soil pyrolization (at every single
temperatures and retention times) ensured for PCB28 and
PCBs concentrations in soil below the reference levels.
Exception to this was the case when a process temperature
of 400°C and a retention time of 30 min where applied. In
this case the PCB28 concentration in soil was of about
0.0492 mg/kgd.w. (4.92 higher than the intervention
concentration – soil for sensitive use). In addition to the
congeners considered by the Romanian MWFEP Order no.
756/1997 [5], during the experimental activities, the most
toxic PCBs [6], PCB77 and PCB126 were also analysed. In
terms of PCB77 removal from contaminated soil, the
pyrolysis technology showed to be an important alternative.
A high efficiency was obtained even for the lowest
temperature (400°C), at two pyrolysis retention times:
98.26% for 30 min. and 94.79% for 60 min. Higher pyrolysis
temperatures (600 and 800°C) ensured maximum
efficiency for PCB77 removal (99.999 %) for both retention
times. Figure 4 and figure 5 illustrate the PCBs
concentration after the pyrolysis of the contaminated soils.
Concerning the PCB126 removal from contaminated soil
functions, the influence of the retention time on the removal
efficiency was observed. For the 60 min retention time,
99.999% removal efficiency was observed in case of the
400, 600 and 800°C process temperatures. Contrary to this,
the retention time of 30 minutes ensured different
efficiencies: from 96.154 % for 400 °C to 98.462 % for 800
°C (fig. 3.a. and fig. 3.b.). Related to pyrolysis tests on PCBs
removal from similar soil matrix suggested that,
considering the economics point of reducing energy
requirements, the lowest retention time at 800°C may be
sufficient for ensuring high pyrolysis efficiency (99.99%)
[7]. In case of the soil artificially contaminated with PCB-
containing transformer oil from the present experimental
study, in terms of the pyrolysis process, a high efficiency of
99.778% for PCBs removal was obtained. Other important
aspects that must be considered in terms of the thermal
treatments methods for soil decontamination are the
emissions of PCBs from soil pyrolysis. For this reason,
emissions of PCB28, PCB77, PCB126 and PCBs were also
analyzed (fig. 6).
Fig. 3a. Pyrolysis of contaminated soil; PCBs removal efficiency for
a 30 min. retention time
Fig. 3b. Pyrolysis of contaminated soil; PCBs removal efficiency for
a 60 min. retention time
Fig. 4. PCBs concentration level in 30 min. pyrolized soil Fig. 5. PCBs concentration level in 60 min. pyrolized soil
REV. CHIM. (Bucharest) ♦ 65 ♦ No. 1 ♦ 2014 http://www.revistadechimie.ro 47
The results concerning the emissions showed that
temperature and retention time have an important
influence on PCBs concentration in the flue gases
generated during the thermal treatment in a nitrogen
atmosphere. However, this is not valid for all thermal
treatments developed in the present experimental study.
Consequently, the retention time has no influence on
emissions due to pyrolysis at 400°C, when the
concentration of the PCBs in the released gases remains
almost of the same value if the soil sample is treated for 30
or 60 min. The effect of the process time is important for
high pyrolysis temperatures (600 and 800°C), when from
30 to 60 min. retention time conducted to two times
concentration levels of PCBs in the pyrogases. This has
happened for every single experiment concerning the
PCB28, PCB77, PCB126 and PCBs behaviors. For instance,
the concentration of PCB28 in the pyrogas formed during
the pyrolysis process decreased with almost 6% from 30
to 60 min. retention time. Thus, the increase of the retention
time decreases the PCB28 concentration level. The same
behaviour was registered if the pyrolysis temperature is
raised from 600 to 800°C (a decrease of 63% was registered
for 30 min. and 53% for 60 min.). According to the results
presented in the figures above, it seems that PCBs
volatilization is the main mechanism for PCBs removal
from contaminated soil under operational conditions
applied in our experiments, phenomenon revealed in
studies carried out by other authors [8] for a similar soil
matrix.
Incineration of the artificially contaminated samples
Results obtained during the experiments demonstrate
that during incineration, PCBs are almost entirely removed
from the contaminated soil. Removal efficiency of PCBs
from the soil is presented in figure 7.a and 7.b for different
process temperatures (600, 800 and 1000°C) at different
retention times of the solid material inside the reactor. As
expected, for all studied cases, the removal efficiency was
over 99%, except the PCB126 at 800°C and 30 min., for
which, the removal efficiency was of approximately 97%.
This could be explained by the temporary increase in
concentration of PCB126 due to cracking mechanism of
the heavier species of PCBs into PCB126.
As figure 8 shows, the volatilisation and removal rates
were higher after 800°C; in case of PCB28; the removal
efficiency increases from 99% (at 600°C) to over 99.9% (at
800 and 1000°C). In this case, the time factor had very
sight influence on PCBs removal from contaminated soil.
From the environmental point of view, as already
mentioned, the Romanian regulations limit PCBs
concentrations within soils based on its utilisation:
agriculture or construction. Even if incineration seems to
be one of the best technologies to remove and destroy
PCBs from soils, it is very important to consider also PCBs
emissions level within the process gas. Figure 9 shows the
concentration of PCBs in flue gas in case of 30 min.
retention time. As it can be observed, all studied congeners
have the same trend.
Higher the temperatures, higher are the differences
between devolatilization and the destruction rates. In order
to completely destroy PCBs from the gas stream, the real
incineration plants are built with a secondary combustion
Fig. 6. Emission concentration level of PCBs from soil pyrolization
(30 min. retention time)
Fig. 7a. Incineration of contaminated soil; PCBs removal efficiency
for 30 min. retention time
Fig. 7b. Incineration of contaminated soil; PCBs removal efficiency
for 60 min. retention time
Fig. 9. Emission concentration level of PCBs from soil incineration
(30 min. retention time)
Fig. 8. PCBs concentration level in soil after the incineration
process
REV. CHIM. (Bucharest) ♦ 65♦ No.1 ♦ 2014http://www.revistadechimie.ro48
Table 2
INITIAL AND FINAL CONCENTRATION FOR THE PCBs OF
CONGENERS AFTER APPLYING ELECTROCHEMICAL TREATMENT
[mg/kgdw]
Fig. 10. The time influence on the removal efficiency of the
electrochemical treatment (12 and 21 days)
Fig. 11. Comparison between pH and ORP variation during the
electrochemical experiment Fig. 12. Current trend in time during the electrochemical treatment
chamber [9] where the gas stream is completely oxidized
for 2 s at temperatures of about 1200°C. In this manner, the
production of future dioxins and furans is avoided.
Electrochemical treatment
As previously underlined, the electrochemical treatment
has been applied on an artificially contaminated soil with
PCB-containing transformer oil and anthropogenic with
heavy metals. The electrochemical treatment was applied
on almost 60 kg of PCB polluted soil, for a period of 21
days. The specific voltage was 1 V/cm; that means an
applied voltage of 50 V (the distance between the
electrodes was set at 50 cm).
As in case of thermal treatment methodologies
illustrated before, the behaviour of PCB 28, PCB 77, PCB
126 and PCBs, prior and after the electrochemical
treatment, were analyzed. The highest initial PCB28
concentration was of 1.3595 mg/kgd.w. (table 2). During
the experiment, a continuous monitoring of the key
parameters has been carried out (electric current, pH, redox
potential and temperature). The soil pH represents a
measure of acidity which plays an important elements and
processes from soils [10-13]. Samples after 12 days, as
well as at the final experiment (after 21 days) have been
characterized in order to determine the concentration
levels for the already mentioned PCBs congeners. The soil
sampling has been done from three different areas: anode,
middle and cathode. The treatment efficiencies have been
assessed as presented in figure 10 and table 2.
Treatment efficiencies for the test performed on PCBs
contaminated soil, increased in time. Concerning the PCBs
concentration level, after 21 days the concentrations in
the electrodes areas are smaller than the intervention
threshold for sensible use mentioned in O756/1997
(removal efficiency ranged from 59% to 85%). If the
attention is focused on PCB 28, the electrochemical
treatment should continue for at least other 2 weeks (over
21 days of the experimental study), considering that a lower
efficiency was obtained: from 53% to 83% related to the
different sampling areas (anode, middle and cathode). The
two PCBs congeners that are toxic for human health
(PCB77 and PCB126) showed good removal efficiencies.
Even if higher removal efficiency was obtained for PCB126
(between 94% and 100%) the results concerning PCB77
could be considered more accurate because of the initial
concentration of two congeners (about 0.0026 mg/kgd.w.
for PCB126 thus, 12 times smaller than the one for PCB77).
Concerning the ORP that was checked across the
experiments, this is a measure of the system ability to
oxidize (accept electrons) or to reduce (donate electrons)
in the system. Consequently, there are ensured conditions
for oxidizing or to reducing other components in the
system. If ORP is positive, less oxidant will be required to
oxidize a component [14 - 16]; in this way, soil or sediment
remediation is expected.
pH is another key parameter of the electrochemical
remediation process with important influence on method
efficiency because is playing a part in the range that
oxidation and reduction can take place. The reason, for
which ORP was monitored during the electrochemical
tests, was both to observe where the oxidation/reduction
reactions took place and to control the treatment efficiency
along the soil sample. Results gained until now and
published in the specialized literature showed that, if
applying a constant voltage to an organic polluted soil and
the changing ORP in a considerable way, a non uniformity
in removing organic pollutant is observed at the end of the
process [17]: higher removal at anode where the oxidation
reaction occurred and smaller at the cathode. With the
aim of avoiding these kinds of results (no uniformity in
removing organic pollutants from soil), during the
experimental tests, the oxidation reactions along the soil
sample were encouraged: every single time when it was
observed that ORP was below 0, the electric potential was
changed and in this way anode became cathode and the
cathode became anode.
REV. CHIM. (Bucharest) ♦ 65 ♦ No. 1 ♦ 2014 http://www.revistadechimie.ro 49
The third key parameter monitored across the
electrochemical tests was the current that has an influence
on the overall costs due to the fact that it will increase the
costs with energy expenditure. Usually when we have a
high value for the current in an area, in the same area we
have strong oxidation reactions.
Results gained throughout the experimental research
concerning the key parameters of the processes are
according to figures 11 and 12.
Conclusions
This paper presents the results of the research on three
decontamination methods for PCBs removal from soil,
namely: pyrolysis, incineration and electrochemical
remediation. For every single decontamination method,
the behaviour of PCB28, PCB77, PCB126, and PCBs has
been studied, using different process parameters. The initial
PCBs concentrations, according to the national regulation,
were 1.3593 mg/kgd.w. for PCB28 and 4.4661 mg/kgd.w for
PCBs. Envisaging the future use of the decontaminated
soils for agriculture, the authors considered the national
acceptable levels for intervention thresholds (sensitive use)
as reference levels. In this case, the results showed that
the initial concentration for PCBs exceeded by our times
the legal limit, while the PCB28 concentration level was of
about 135 times in excess. With respect to the process
temperature of 600 and 800°C for the thermal treatment
methodologies, our results showed that both pyrolysis and
incineration are efficient methods for removing PCB28,
PCB77, PCB126 and PCBs from contaminated soils,
generally attaining an efficiency of over 99%, independently
of the process parameters. Exception to the rule was
PCB126 that seems to be more difficult to be removed
from soil at 600 and 800°C for 30 min.: for pyrolysis the
efficiencies were 98.077 and 98.462%, respectively, while
for incineration, 98.367 and 95.769%, respectively. As
expected, the lower pyrolysis process temperature at
400°C for 30 min. retention time ensured a lower efficiency
of 97.349%, and the higher incineration process
temperature of 1000°C for both 30 min. and 60 min.
retention times, guaranteed higher efficiencies, in
particular, over 99%. Even though, thermal treatment
ensured high efficiencies, it must be said that, special
attention should also be paid to emission levels and energy
consumption. Also for this reason, research was additionally
focused on electrochemical remediation. The temporary
results (after 12 days), as well as the final ones (after 21
days), pointed out that PCBs concentration levels
exceeded the nationally acceptable levels for intervention
thresholds (sensitive use) and a high efficiency was gained
just for PCB126 removal (over 99%). This is an important
aspect if one would take into account that, in case of the
thermal treatment, PCB126 removal was problematic. With
regard to other congeners and PCBs, the results indicated
that, in order to have higher efficiency, the electrochemical
treatment needs more time. Future research will be
focused on costs, environmental impact and energy
consumption in relation with the tested remediation
methods.
The subject has been also studied in [18].
Acknowledgment: The authors would like to thank the National
Authority for Scientific Research–Romania; the present work was
developed under the Sectorial Operational Programme “Increase of
Economic Competitiveness” POS-CCE-A2–O2.1.2.-2009-2, RECOLAND
project (ID519), SMIS-CSNR: 11982, Nb. 182/18.06.2010 (2010-2013) and
PN II Program - CAPACITIES (Module III) - Romanian-Turkish Bilateral
Agreement, RISKASSESS, contract no. 606/01.01.2013 (2013 – 2014).
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Manuscript received: 12.03.2013
