Journal of Environmental Protection, 2013, 4, 1495-1501
Published Online December 2013 (http://www.scirp.org/journal/jep)
http://dx.doi.org/10.4236/jep.2013.412171
Open Access JEP
1495
Surfactant-Enhanced Washing of Soils Contaminated with
Wasted-Automotive Oils and the Quality of the Produced
Wastewater
Montserrat Zacarias-Salinas1, Mabel Vaca2, Miguel A. Flores2, Erick R. Bandala3, Luis G. Torres1*
1UPIBI-Instituto Politécnico Nacional. Av. Acueducto s.n. Colonia Barrio la Laguna Ticomán. México DF, México; 2Labor-
atorio de Calidad de Agua y Residuos, Universidad Autónoma Metropolitana-Unidad Azcapotzalco México; 3Departamento de
Ingeniería Civil y Ambiental Escuela de Ingeniería, Universidad de las Américas-Puebla. Sta. Catarina Mártir, Cholula, Puebla,
México.
Received February 16th, 2013; revised March 19th, 2013; accepted April 15th, 2013
Copyright © 2013 Montserrat Zacarias-Salinas et al. This is an open access article distributed under the Creative Commons Attribu-
tion License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly
cited. In accordance of the Creative Commons Attribution License all Copyrights © 2013 are reserved for SCIRP and the owner of
the intellectual property Montserrat Zacarias-Salinas et al. All Copyright © 2013 are guarded by law and by SCIRP as a guardian.
ABSTRACT
An old automotive industrial site located at Mexico City with many years of operation and contaminated with heavy oil
hydrocarbons, particularly spent oils, was assessed for restoration using the surfactant enhanced soil washing (SESW)
process. The main goal of this study was to characterize the contaminated soil in terms of TPHs, BTEX, PAHs, and
metals contents as well as microbiologically (total heterotrophs and specific degrading microorganisms). We also aimed
to determine the surfactant type and concentration to be used in the SESW process for the automotive waste oil con-
taminated soil. At the end, sixteen kg of contaminated soil were washed and the produced wastewater (approximately
40 L) was characterized in terms of COD, BOD; solids, and other physico-chemical parameters. The soil contained
about 14,000 mg of TPH/kg soil (heavy fraction), 0.13 mg/kg of benzo (k) fluoranthene and 0.07 mg/kg of benzo (a)
pyrene as well as traces of some metals. Metals concentrations were always under the maximum concentration levels
suggested by Mexican regulations. 15 different surfactants were used to identify the one with the capability to achieve
the highest TPH removal. Surfactants included 5 anionics, 2 zwitterionic, 5 nonionics and 3 natural gums. Sulfopon 30
at a concentration of 0.5% offered the best surfactant performance. The TPH removals employing the different surfac-
tants were in the range from 38% to 68%, in comparison to the soil washing with water (10% of TPH removal). Once
the surfactant was selected, 70 kg of soil were washed and the resulting water contained approximately 1300 mg/L of
COD, 385 mg/L of BOD (BOD/COD = 0.29), 122 mg/L of MBAS, and 212 mg/L of oil and greases, among other con-
taminants.
Keywords: Wasted Automotive Oils; Surfactants; Soil Washing; Waste Water
1. Introduction
The restoration of soil contaminated with hydrocarbons
is often difficult and complex due, among other, to the
adsorption on the soil matrix and the low solubility of
these contaminants. It has been demonstrated that the
more insoluble in water is the contaminant, the longer it
remains in the soil matrix [1].
Many different techniques have been reported to re-
store soils contaminated with hydrocarbons; among of
them the surfactant-enhanced soil washing (SESW) have
recently emerged as highly cost-effective [2-4]. Surfac-
tants reduce surface tension and form aggregates (i.e.
micelles in aqueous solution), changing surface tension
as result of surfactant’s concentration on the solution’s
surface. Contaminants present in soil are removed by
means of two phenomena: 1) The solubilization of com-
pounds due to the reduction of surface tension (bellow
the surfactant’s critical micelle concentration (CMC) and
2) The mobilization of hydrophobic compounds due to
the presence of the surfactant, at concentrations higher
*Corresponding author.

Surfactant-Enhanced Washing of Soils Contaminated with Wasted-Automotive
Oils and the Quality of the Produced Wastewater
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than surfactant’s CMC value [5].
SESW process has shown very good results, and also
has been considered as an economic and easy technique,
so its application has increased in interest [3,6-9] as
shown the literature review. Iturbe et al. [6] reported
TPH (Total Petroleum Hydrocarbons) removals over
92% for contaminated soil with an initial concentration
up to 17,238 mg/kg, when washing contaminated soils
using the surfactant Canarcel TW80 in concentrations of
about 0.5%. In other studies with SDS (sodium dodecyl
sulphate), TPH removals above 90% were reported when
treating oil-hydrocarbons contaminated soils [10].
Chin-Chi et al. [11], when washing contaminated soil,
showed high TPH removals, between 63% and 62%,
respectively using biosurfactants (i.e. rhamnolopids and
surfactin) for the SESW process in a soil contaminated
with a 9000 mg/kg of hydrocarbons. These authors also
used two synthetic surfactants (Triton X-100 and Tween
80) for the same washing process, finding that synthetic
surfactants were clearly less efficient (40% and 35%,
removal, respectively). Another experiment using a non-
ionic surfactant Brij 35 showed removals of crude oil
from soils of 93.54% in a surfactant-enhanced washing
of soil contaminated with 50,000 mg/kg of crude oil [12].
In this work, an old automotive industrial site located
at Mexico City was assessed for restoration using SESW.
The site maintains operations for many years and pro-
duced contamination with heavy oil hydrocarbons, in
particular spent oils. Car service activities were carried
out in the place, such as automotive oil change service,
and wasted oils were stored in a submerged cement tank
for many years. The company suspended its service more
than 10 years ago and closed. The place was dismantled
to become a residential zone.
During the process of characterization the site, which
was carried out by the UAM-Azcapotzalco (Mexico), it
was noticed that the oil cement tank suffered spills caus-
ing infiltration of the automotive oil waste in a large area
of the old industry, contaminating the subsoil in an im-
portant extent. The soil contained about 14,000 mg of
TPH/kg soil referring to heavy fraction (The analysis of
the TPHs present in the soil was made by the suggested
methodology in Mexican standard using dry soil). The
maximum permissible limit established by Mexican
regulations concerning contaminated soil with heavy
fraction petroleum hydrocarbons suggests reducing the
concentration of the site up to 6000 mg/kg.
The main goal of this study was to characterize the
sub-soil of the old automotive industry, in terms of TPHs,
BTEX (benzene, toluene, ethylbenzene and xylene),
PAHs (polycyclic aromatic hydrocarbons), and a set of
metals as well as microbiologically. To show the suit-
ability of SESW process to remediate the site, including
surfactant type selection and concentration to be used in
the processes. Finally, the generated wastewater was
characterized in terms of COD (chemical oxygen de-
mand), BOD (biochemical oxygen demand), solids, and
other parameters in order to determine the kind of proc-
ess most suitable to treat the effluent to recycle the water
into the soil washing process or to be disposed at the end
of the soil remediation process.
2. Materials and Methods
2.1. Soil Sampling
The soil samples were taken from the subsoil of the site
using a 25 SCRS Giddings model hydraulic punch (Fig-
ure 1), taking samples from 1.5 to 3.0 m deep, extracting
about 70 kilograms of wet soil, which were stored in
polypropylene black bags to avoid photo-degradation of
pollutants and placed into pet boxes were they were
maintained at room temperature during a period of 2
weeks before the experiments. Soil was thoroughly
mixed to assure that concentrations of TPH as well as
other organic and inorganic components were uniform
for the whole batch of soil.
2.2. Soil Characterization
The composed soil sample was dried at room tempera-
ture for 3 days. The final moisture content in the soil was
determined 10%, measured by mass difference. The
physico-chemical characterization of the soil was carried
out including texture, bulk and particle density, pore
space, total and bioavailable nitrogen and phosphorus
and conductivity measurements. TPH’s, the 16 PAH
(Polycyclic aromatic hydrocarbons) normed by USEPA
and BTEX were also determined. Finally, some metals
and metalloids concentrations (Na, K, Ca, Mg, As, Cd,
Zn, Cu, Cr, Pb, Ni, Hg and Fe), were determined in the
soil sample. The analyses were performed based on EPA
Figure 1. (a) Hydraulic punch employed at the sampling
process; (b) Helicoidal drilling device.

Surfactant-Enhanced Washing of Soils Contaminated with Wasted-Automotive
Oils and the Quality of the Produced Wastewater
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standard methodology suggested in Mexican regulations,
for TPH content the methods were EPA 9071B and
EPA1664A.
The microbiological assessments were applied to the
contaminated soil in order to determine the amount of
present microorganisms. Plate counts were carried out
using nutritive agar Petri dishes for heterotrophic bacteria
count and for hydrocarbon degrading bacteria, diesel,
gasoline or automotive-oil waste was employed as car-
bon source. The mineral medium used was as follows (in
mg/L): KH2PO4, 8.5; K2HPO4, 21.75; Na2HPO4 * 7H2O,
33.4; NH4Cl, 1.7; MgSO4 * 7H2O, 22.5 CaCl2, 27.5;
FeCl3 * 6H2O, 0.25. These mineral media was adapted
from the one suggested in a Mexican standard employed
to determine BOD (NMX-AA-028 in NOM-001-SE-
MARNAT-1996). The bacteria were incubated at 30˚C
over a period of 48 to 96 hours for heterotrophic and hy-
drocarbon degrading bacteria. The quantities of bacteria
were expressed as a CFU/g of dry soil.
2.3. Washing Solutions
Five anionic surfactants were used: sodium dodecyl
sulfate (SDS), sodium bencen-dodecyl sulfonate (SDBS),
Texapon N40 (TN40), Sulfopon30 (S30) and Surfacpol
A14104. The five nonionic surfactants employed along
this work were Tween 80 (TW80), Tween 20 (TW20),
Span 80 (SP80), Brij 35 (B35) and Emulgin W600 (EW).
Two zwitterionic products were employed: Polafix
CAPB and Polafix LO. Finally, three natural gums (ca-
pable to act as a surfactants/emulsifiers) were employed,
i.e., locust bean gum (LGB), guar gum (G) and mezquite
seed gum (MZ). Distillated water was used as a blank for
soil washing assessments. Some characteristics of the
employed surfactants are shown in Table 1.
Two sets of soil washing experiments were performed;
the first set was carried out using synthetic surfactants
(anionic, nonionic and zwitterionic) concentrations of
0.5% and 0.1% for natural gums. In the second set of
assessments, different concentrations of surfactants were
tested of 0.25%, 0.5% and 1% for the synthetics surfac-
tants and 0.05%, 0.1% and 0.2% for natural gums.
2.4. Soil Washing
The SESW experiments were carried out in 40 mL glass
vials, where 6 g of contaminated soil dried at room tem-
perature were added together with 20 mL of the washing
solution or water. The vials were shaken at 200 rpm for a
period of 23 hours and, then, they allowed to settle for an
hour.
2.5. Measurement of TPH’s in Soil Washing
After washing the soils, supernatant was separated and
stored in the freezer until further analysis. The washed
soil samples were placed in aluminum trays to be dried at
room temperature (25˚C) for 3 days. Then TPH’s con-
centration was determined by a gravimetric method after
Soxhlet extraction using hexane as a solvent, described in
Section 2.2. Soil humidity was determined and taken into
account to report mg of heavy fraction/g of dry soil using
the methodology suggested in Mexican standards.
Table 1. Some characteristics of the employed syntetic surfactants.
Surfactant Ionic natureChemical name Mol weight (g/gmol)HLB CMC (mg/L) Reference
SDS Anionic Sodium dodecyl sulfate 288.4 40 400 [13]
SDBS Anionic Sodium dodecyl-bencenesulfonate322.37 NR 1.5 [14]
Texapon 40 Anionic Sodium lauryl ether sulphonate 442 NR 1458 [13]
Sulfopon 30 Anionic Sodium lauryl sulphate 272 NR 150 This work
Surfacpol A14104 Anionic NR NR NR NR [14]
Tween 80 Non-ionic Sorbitan monoleate (Poe 20) 1308 15 65.4 [13]
Tween 20 Non-ionic Sorbitan monolaurate 1226 16.7 60.74 [13]
Span 80 Non-ionic Sorbitan monooleate 428 NR NR
Brij 35 Non-ionic Lauric alcohol ether 1206 16.7 NR [14]
Emulgin W600 Non-ionic Nonyl phenol 483 11 45.06 [13]
Polafix CAPB ZwitterionicCocoamide-propyl Betaine NR NR 80 [14]
Polafix LO ZwitterionicNR NR NR NR -
HLB: Hydrophilic Lipophilic Balance; CMC: Critical Micelle Concentration; NR: Not Reported.

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Oils and the Quality of the Produced Wastewater
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3. Results and Discussion
3.1. Soil Characterization
Table 2 shows some of the physical and chemical char-
acteristics of the soil employed in this study. As shown
the content of organic matter, nitrogen and phosphorus;
are interesting because suggest the possibility of applying
biological treatment to the resulting waste water. The
moisture content of the soil was 40%. The conductivity
of the soil was normal in the case of a clayish soil
(0.3058 μS/cm), as well as the pore space percentage
(66%). The report suggests that pH is mildly basic. The
organic matter content indicates a moderately rich soil.
However, the nitrogen content in the soil is poor, con-
trasting with the very high contents of phosphorus. Met-
als and metalloids concentrations in soil (Table 2), were
reported were below the limits set in Mexican regulation.
Two bacteria count processes were applied to the con-
taminated soil, heterotrophs and hydrocarbon degraders
(diesel, petroleum and automotive oil waste). The results
showed an heterotrophic microorganisms count of 4.1 ×
107 CFU/g. Regarding the specific degraders, values of 1
× 108 CFU/g, 1.5 × 108 CFU/g and 1 × 108 CFU/g were
found for diesel, petroleum and automotive waste oil
degraders, respectively. The microbial count was similar
to that reported by Iturbe et al. [6] for a soil contami-
nated with PAHs where bacteria counts of 1.8 × 108
CFU/g for heterotrophic and 5.4 × 108 CFU/g, 1 × 108
CFU/g and 5.6 × 108 CFU/g for diesel, petroleum and
spent oil bacteria were reported. These values are higher
Table 2. Physicochemical characteristics of the contami-
nated soils.
Parameter Result Parameter Result
Conductivity 0.3058 µS/cm Pb 19.32 mg/kg
pH 8.5 Fe 4432.65 mg/kg
Apparent density 1.02 g/cm3 Zn 13.60 mg/kg
Bulk density 3.0 g/cm3 Na 652.22 mg/kg
Void space 66% K 949.65 mg/kg
Soil percentual
composition
60% clay
30% silt
10% sand
Ca
Mg
As
23855.82 mg/kg
14401.59 mg/kg
1.78 mg/kg
Texture Clayey Cd 2.80 mg/kg
Organic matter 2.12 % Cu 6.73 mg/kg
Total phosphorus 605.60 mg/kg Cr <1.0 mg/kg
Available
phosphorus 18.80 mg/kg Ni 9.87 mg/kg
Total nitrogen 0.058% Hg 0.11 mg/kg
Avail. nitrogen 9.93 mg/kg
than those reported by Bogardt and Hemmingsen [15] for
soils contaminated with diesel and petroleum oil (1.9 ×
107 CFU/g and 3.3 × 107 CFU/g, respectively). On the
other hand, Hernández-Espriu et al. [16] reported a bac-
terial count of 2 × 1011 FCU/g for an agricultural soil
contaminated with diesel. The observed amounts of mi-
croorganisms are higher than the minimum necessary for
biodegradation process (104) stated by Fahnestock [6,16].
Regarding the analysis of PAHs, BTEX and TPHs, it
was found that only the heavy fraction hydrocarbons ex-
ceeded the permissible limits established by Mexican
legislation (Table 3). No BTEX were determined over
the method detection limit and only two PAHs were
found from the 16 PAH’s regulated by USEPA. These
PAHs, however, were found with concentrations below
the maximum permissible limits established in the Me-
xican standards (Tabl e 4 ). No light fraction oil content in
the media was found indicating that the contamination
was due solely to automotive waste-oil spills.
Despite the good performance and applications of sur-
factants for the transference of hydrocarbons into water,
the removal efficiency depends also on several factors
including nature, amount of surfactants, age of contami-
nated soil, soil properties and surfactant/oil/soil system
behavior [10]. The highest removals were observed for
Table 3. Mexican standards for PAHs, BETEX and TPHs.
Maximum concentrations (mg/kg dry soil)
Parameter Agricultural
soil Residential soil Industrial soil
TPHs
Light fraction 200 200 500
Median fraction 1200 1200 5000
Heavy fraction 3000 3000 6000
BTEX
Benzene 6 6 15
Toluene 40 40 100
Ethylbenzene 10 10 25
Xylene 40 40 100
PAHs
Benzo (a) pyrene 2 2 10
Dibenzo (a,h) antracene2 2 10
Benzo (a) antracene 2 2 10
Benzo (b) fluorantrene2 2 10
Benzo (k) fluorantrene8 8 80
Inden (1, 2, 3, cd) pyrene2 2 10

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Table 4. TPH’s and some PAH’s present in the contami-
nated soils.
Parameter Results (mg/kg)
TPH’s (heavy fraction) 14,705
Benzo (k) fluoranthene 0.1280
Benzo (a) pyrene 0.0682
Sulfopon 30, Tween 20, CAPB Polafix and mezquite
seed gum with 59%, 54%, 52% and 55% of TPHs re-
moval respectively. Zamudio-Pérez et al. [17] reported
TPHs removals of 57.7% when washing an oil-con-
taminated soil, employing Brij 35 (Figure 2). They also
tested natural gum as washing solutions. The best TPHs
removal for natural gums was obtained with locust bean
gum (31%).
The second set of washing assessments different sur-
factant concentrations was carried out with the best of
each type except mezquite seed gum. The last was re-
placed by guar gum because mezquite seed gum is not a
commercial surfactant and its production method is com-
plex. Three concentrations for every surfactant were eva-
luated in the second washing procedure. It was observ-
ed that Sulfopon 30 (0.5%) achieved the highest per-
centage of removal 60%.
Tween 20 (TW20) rendered removal efficiencies of
20%, 54% and 55% with solutions of 0.25%, 0.5% and
1% respectively. CAPB showed similar behavior, in this
case, removals of 53% and 54% were achieved using
concentration of 0.5% and 1% (Figure 3).
Regarding the TPHs removal efficiency using guar
gum, it was observed that the concentration of 0.1% pro-
duced the best result, reaching 54%. Same result as in the
first wash. It is noteworthy that although it was not the
highest removal percentage the experimental set showed
the greatest amount of TPHs removal per gram of prod-
uct (Figure 4), as the washing solutions used has lower
concentration than synthetic ones.
In experiments made before, the standard deviations
were not over the 5%, in this experiment the analysis
showed the same behavior.
3.2. Characterization of the Generated
Wastewaters
The scaling-up of the washing process were carried out at
the best conditions. In order to do that 16 k of soil were
washed with Sulfopon 30 at 0.5%. Approximately, 40 L
of wastewater were produced and characterized in terms
of COD, BOD5, turbidity, electrical conductivity, color,
hardness, MABS (methylene blue active substances), oils
and greases, as well as 4 selected metals. Results are de-
picted in Table 5 . As shown COD value was above 1300
Figure 2. TPHs removals for the 15 washing solutions and
water.
Figure 3. TPH’s removals when using different surfactants
concentrations for SP30, TW20 and guar gum.
Figure 4. TPH’s removals per mg of surfactant employed.
mg/L which is below the reported by Bandala et al. [18]
for refinery wastewater. Measured of BOD concentration
was 380 mg /L generating a BOD5/COD ratio of 0.29
rating the wastewater as poorly biodegradable. Torres et
al. [19] reported a rate of biodegradation on 41.7%
(moderately biodegradable) of soil washing waste water
from a site contaminated with hydrocarbons. The higher
COD and BOD values obtained are due to the oil content

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Oils and the Quality of the Produced Wastewater
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Table 5. Characteristics of the produ ced waste wate r.
Parameter Result
Zamudio Perez
et al. [17]* Torres et al. [3]
COD 1329 mg/L 1468.0 mg/L 20,153 mg/L
BOD5 385 mg/L 289.6 mg/L 8410 mg/L
BOD5/COD 0.29 0.197 0.41
Turbidity 1540 FAU 525 UNT NR
Conductivity 1107 µS 2580.0 µS 1,353 µS
Color 92 Pt/Co 3625 Pt/Co NR
Hardness as CaCO3 489 mg/L 22.50 mg/L 337.31 mg/L
MBAS 122 mg/L 0.015 mg/L 3368.0 mg/L
Oil and greases 212 mg/L 6.0 mg/L 94.5 mg/L
Pb 0.401 mg/L 20.13 mg/L 1.11 mg/L
Fe 19.05 mg/L 11.25 mg/L 289.64 mg/L
Cr 0.07 mg/L 0.023 mg/L 1.25 mg/L
Al 24.21 mg/L 23.62 mg/L 429 mg/L
*When using TW80.
in the soil and the surfactant used in the washing pro-
cedure.
Differences in organic content for the wastewaters
produced in this work, and those reported by Torres et al.
[19] are significant. Nevertheless, it is important to re-
mark that the produced wastewater characteristics will
derive from several factors, i.e., 1) the soil type (sandy,
loamy, clayey); 2) the contaminant type (light, medium,
or heavy fractions in the case of oil derivatives); 3) the
history of the contaminated soil, subjected to aging proc-
esses (young versus old spills); 4) the efficiency of the
washing system (surfactant type and concentration, soil/
water ratio, energy input).
As observed, similar values for conductivity, hardness,
the four selected metals and even for oil and greases
were found. Important differences can be observed be-
tween the wastewaters generated in this work, and those
reported by Torres et al. [19], when comparing COD (15
fold), BOD (21.8 fold) and the BOD/COD value (1.4
fold). It is interesting to note that MABS and oil and
greases values were rather different (27.6 and 0.44 fold,
respectively).
There is very little information on quality of wastewa-
ters produced during the washing of contaminated soils;
however, the characterization of these effluents is rele-
vant regarding its treatment [17,19,20].
4. Conclusions
In the selection of a surfactant for a washing soil, it could
be helpful to propose different type of surfactants to
identify the higher removal of the contaminant. Also it is
necessary to establish the concentration of the surfactant
at the greater removal.
The removal of TPH’s by soil washing vary for each
type of surfactant, in this case, the greater removals were
observed after using the SP30, however when looking at
the milligrams of TPH removed for each gram of sur-
factant employed, the natural gum removed more TPH,
because the concentrations required were five times lo-
wer. The characterization of the resulting water is rele-
vant due to the treatment as suggested of the high rates of
removal of TPH’s also the containing of the surfactant
used in the washing process.
Our research group is working on the treatment of the
generated wastewaters in a low-cost packaging material
submerged biofilter inoculated with hydrocarbon-degra-
der microorganisms isolated from the original conta-
minated soil. Besides, the changes in the biofilter mi-
cro-flora due to the system operation (i.e., residence time,
wastewater COD initial concentration and surfactant con-
centration) are being evaluated using DGGE technology.
5. Acknowledgements
Authors thank to S. Martinez and C. Serrano (Laborato-
rio de Calidad de Agua y Residuos UAM-Azcapotzalco)
because their help in the soil sampling procedure. The
help of C. Orozco (UPIBI-IPN) in the production of the
wastewaters in an agitated tank is also acknowledged.
This work was financially supported by SEP-CONACyT
(Grant 084080).
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