Potential benefit of surfactants in a hydrocarbon contaminated soil washing process: Fluorescence spectroscopy based assessment
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Journal of Hazardous Materials 219 220 (2012) 141 147
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Journal of Hazardous Materials
jou rn al h om epage: www.elsev ier .com
Potenti on proces ss
Amandina Environmenta , UKb School of Life
a r t i c l
Article history:Received 10 OReceived in reAccepted 26 MAvailable onlin
Keywords:Soil washingHydrocarbon cFluorescenceSurfactantTween80
tion tcentrhe efocarbtionst 1% (d 65%ion (9d sanemov
in the soil washing sedimentation process, enhancing sludge/water volume separation by 10% over thewater only wash. In summary, uorescence spectroscopy proved an effective technique to compare TPHremoval efciencies as part of soil washing laboratory based treatability testing.
2012 Elsevier B.V. All rights reserved.
Soils conyaromatic techniques hand is a chowever, thimpede thegravel and in the ne taminants asurfactantscess.
Many aring processcontaminanare in the monly. Contafractions suSpecically
Corresponburgh EH14 4A
taminated with aromatic hydrocarbons, including pol-hydrocarbons (PAH) are often slow to remediate bysuch as bioremediation . Soil washing, on the otheromparatively rapid soil remediation technique ,e hydrophobic nature of aromatic hydrocarbons can
effectiveness of the water only wash process to cleansand fractions and thereby concentrate contaminationsolid fractions . Therefore, particularly where con-re coated or adsorbed onto gravel and sand fractions,
are of potential interest to improve the cleaning pro-
ticles researching the use of surfactants in the soil wash- refer to removal efciency as the ability to concentratets into the liquid phase (efuent) [6,7]; however, theseain based on soils consisting of a single (sand) fraction
minant removal efciency in soils consisting of multiplech as gravel, sand, silt and clay are more complicated., contaminant removal efciency can be considered in
ding author at: School of Life Sciences, Heriot-Watt University, Edin-S, Scotland, UK. Tel.: +44 0131 451 3974; fax: +44 0131 451 3009.ress: email@example.com (T.J. Aspray).
terms of the removal from a particular solid fraction or, the transferfrom the soil to the liquid efuent. Given that the objective of soilwashing is to recover the gravel and sand fractions, contaminantremoval efciency should address these fractions specically. Inaddition, as the silt and clay fractions are usually heavily contam-inated and often require disposal, it may be better to concentratecontamination in silt and clay rather than the liquid efuent. Assuch, surfactants which primarily enhance the desorption of con-taminants from gravel and sand fractions, without necessarilyincreasing contaminant water solubility are of interest.
Numerous studies have assessed the potential of chemical sur-factants such as SDS, Brij 35 or Tween80 to improve removalefciency of contaminants in the soil washing process; the results ofwhich are that surfactants show varying contaminant removal ef-ciencies. With the relative performance of a particular surfactantsbeing soil specic, laboratory based treatability tests are benecialto decide the most appropriate surfactant for a specic soil andsite. For example, Surfacpol has been shown to be more effectivethan Tween80 or SDS in sand , whereas, Tween80 and Brij35 hadsimilar removal efciencies in a sandy loam soil .
In addition to the choice of surfactant, many studies havefocused on dening optimal washing parameters for the surfac-tant, for example, the inuence of washing time, temperature, aswell as surfactant concentration [7,10]. In these previous articles,washing times varied from 5 min to 48 h; however, in order to have
see front matter 2012 Elsevier B.V. All rights reserved.rg/10.1016/j.jhazmat.2012.03.071al benet of surfactants in a hydrocarbs: Fluorescence spectroscopy based asse
e Uhmanna, Thomas J. Aspraya,b,
l Reclamation Services Ltd, Westerhill Road, Bishopbriggs, Glasgow G64 2QH, ScotlandSciences, Heriot-Watt University, Edinburgh EH14 4AS, Scotland, UK
e i n f o
ctober 2011vised form 3 March 2012arch 2012e 3 April 2012
a b s t r a c t
Soil washing is an ex situ soil remediamajor gravel and sand fractions, conaddition of surfactants can improve tcence spectroscopy to assess the hydrgas chromatography. Three wash solusoil: water, Sea Power 101 (SP101) athe gravel and sand was SP101 (54 anmoved contamination to the silt fractremoval efciency from the gravel anthan water wash). In addition to TPH r/ loc ate / jhazmat
contaminated soil washingment
reatment process. The purpose of soil washing is to clean theating contamination into the ne silt and clay fractions. Theciency of this method. Here we report the use of UV uores-on cleaning process as a rapid and cost effective alternative to
were tested on a total petroleum hydrocarbon contaminatedv/v) and Tween80 at 0.5% (w/v). The most effective to wash
improvement over the water only wash, respectively) which4% of contaminants). Tween80 appeared not to enhance TPHd fractions but did concentrate TPH in the efuent (95% moreal from gravel and sand, SP101 also showed potential benet
142 A. Uhmann, T.J. Aspray / Journal of Hazardous Materials 219 220 (2012) 141 147
a time-efcient treatability test and to mimic currently availablesoil washing plant, washing duration should last minutes ratherthan hours. Finally, articial ageing of pollution has also been stud-ied, although in reality, ageing of pollution is not a variable in soilwashing tresoils which
In recensidered forBiosurfactaing microorsaliva) anddate, biosucompared removal efremoval thSDS [14,15excellent bconditions effective [1
In additfractions, thave an inFlocculatingcess and soalso needs can reducefactants andchemical tyinvolving suprocesses.
Finally, performancgravimetricphy in partiinterest as aretains a hi
The aimfactants (thSea Power soil. Specifrom gravelcompared tciency was cost effectitreatability
(1) Deionis(2) Sea Pow
tant proconcentby ourscomparmicelle rescencBriey, orescenorder toand 384
Table 1Soil characteristics.
Moisture content 16.8%pH 6.2
istor oil ran b
of fr 1 l oin wpasswash63lyze
c whole soil (mg/kg)283.85549.95
c gravel only fraction (mg/kg)90.85
0 at 0.5% (Tween80); a non-ionic surfactant (Fisherc, Loughborough, UK). The concentration was chosenn previous articles .
tions were prepared in a 2.5 L container with deionised
ns for occulation test
ed water (hereafter referred to as water),hloride at 0.5% (v/v) (FeCl3); a occulating agent,er at 1% (v/v) (SP101),er at 1% (v/v) and ferric chloride at 0.5% (SP101&FeCl3),0 at 0.5% (w/v) (Tween80),0 at 0.5% (w/v) and ferric chloride at 0.5% (v/v)80&FeCl3).
ically hydrocarbon contaminated soil was taken from aenery located in Ayrshire, Scotland, UK. Soil character-e found in Table 1.
wash solution, three replicate experiments were con-wing the stages below:
esh soil, previously sieved through 8 mm, was mixedf wash solution and stirred for 20 min. A wash time ofas chosen based on previous reports . This mixtureed through two sieves (3.35 mm and 63 m aperture)ed with an additional 500 ml of wash solution.m fraction was allowed to settle for 5 h (correspond-e where no signicant reduction in sediment height
). After which, the resulting supernatant was removed. soil fractions were oven-dried.e resulting solid fractions; gravel (>3.35 mm), sand
and silt/clay (
A. Uhmann, T.J. Aspray / Journal of Hazardous Materials 219 220 (2012) 141 147 143
Fig. 1. Peak loTween80 and
The expeferent pa30 min, 130 min ona spectroter).
The petrngerprint concentratithe intensit.
UVF speter (Gilden pwith 10 ml Loughboroushaker. ThePTFE lter.as soils. Iniand wastew(EEM) scanically, totalexcitation wstep of 5 nmwith the reand concenrelationshipcentration was consisttion range. necessary. TNewbury, M5 ppm (EDR
Tween80Even thougare in diffetamination using the EMcarbon contTherefore, t
Table 2Compensation factors for the surfactant inuence on TPH analysis.
.005%5% C% C
tion ition tion e facthat nly umentfacton exrfactardizeactios whactio. By ct shpe re
Surfa TPHfor ta), w80 apgravereatehen
ed tolity i
und wt impiclescy, Tr parrmincicsh sns becation on the excitation emission matrix (EEM) map of TPH, PAH,SP101.
riment lasted 3 h. During this time the evolution of dif-rameters was studied. At each chosen time (0, 10 min,
h, 2 h and 3 h) the sludge height was taken, and fromwards, total suspended solids (TSS) was analyzed usingphotometer (Hach DR 2800 Portable Spectrophotome-
olet uorescence (UVF) spectroscopy analysis
oleum products have a specic location within the EEM[23,24]; but the peak can move in the map with theon . However, within a specic calibration range,y can be used to nd the contaminant concentration
ctroscopy was carried out using a FluoroSENS uorime-otonics Ltd, Glasgow, UK). Soil, 5 gdryweight was mixedHPLC uorescence grade methanol (Fisher Scientic,gh, UK) and shaken for 5 min using a reciprocating
resulting supernatant was ltered using a 0.45 m Efuent samples were ltered in the same mannertial characterization of hydrocarbon in the soil extractaters was carried out using excitationemission matrix, after which an emission (EM) scan was used. Specif-
petroleum hydrocarbon (TPH) was analyzed at anavelength of 285 nm and emission 300355 nm with. The area under the resulting curve was calculated
ctangle method. A linear relationship between areatration was found with a coefcient of R2 = 0.959. This
was used to determine the total aromatic TPH con-in studied samples. Maximum uorescence intensityent at the wavelengths employed within the calibra-Sample extracts outside of this range were diluted as
If C < 0If 0.00If 0.03
compeused [2centrain addcentrathen thGiven was oexperisation with athe sustandasand frprolesand frand b)efuenenvelo
lower (Fig. 3Tweenin the even gment wappearvariabiinated
Althwas fobiggesfew artefciensmalleBy detethe spethe wafractiohe calibration kit came from SiteLab Corporation (WestA, USA) consisting of ve standards between 0.1 andO Diesel Range Hydrocarbons; product #CAL-042).
ant effects on the analysis
and SP101 both uoresce when excited with UV light.h the surfactants maximum uorescence intensitiesrent locations to the soil extracted hydrocarbon con-(Fig. 1), TPH analysis of surfactant washing solutions
scan showed that both surfactants inuenced hydro-aminant analysis at the 285 nm excitation wavelength.o allow for the surfactant inuence on UVF analysis, a
process). Thand Tweenwhereas, SPAs such, theenhancing comments of gravel fra
By analy(and the efior of the more effect(Fig. 3c), wcontaminatsolid fractiprojects, co 0.92 If C < 0.005% 0.95 < 0.03% 0.84 If 0.005% C 1% 1
2.9357C0.1993 0.5% 111.112C+1.2529
ion factor was determined experimentally as previouslyhe factor was specic to the surfactant and was con-
dependent (i.e. non-linear) presumably due to effectsto uorescence emission (Table 2). The surfactant con-was determined by the dilution used for the analysis;tor was applied on the calculated area described above.the heat destroys the surfactant  the compensationsed for the efuent analysis. Moreover, we foundally further justication for not applying the compen-r to the solid fraction analysis (Fig. 2). In particular,
citation scan at xed emission wavelength of 430 nmnt inuence was observed; the resulted curves wered before being compared. The results show that then extracts of the surfactant washes had uorescenceich associated more closely with the water only washn extracts than the original surfactant solutions (Fig. 2aomparison, the uorescence proles of the surfactantowed clear differences in the shape of the emissionlative to the water only wash efuent (Fig. 2c and d).
f surfactants on TPH in a soil washing process
ctant effects on TPH in solid fractions concentration in the gravel fraction was signicantlyhe SP101 wash when compared to water only washith a 54% washing improvement. By comparison,peared not to have a signicant effect on TPH removall fraction. For the sand fraction (Fig. 3b), SP101 had anr effect on TPH removal with 65% washing improve-
compared to the water only wash. Although Tween80 enhance TPH removal in the sand fraction, the inherentn contaminant concentration in the historically contam-revented us from drawing this conclusion.
h an improvement in contaminant removal efciencyhen using surfactant SP101 for the gravel fraction, the
rovement was on the sand fraction. Despite generally having studied the effect of particle size on the removalorres et al.  found removal was more effective for
ticle size fractions, which corroborates with our results.ing the initial TPH concentration in the gravel (Table 1)
removal efciency on gravel was also calculated for allolutions (this stage could not be done with the othercause of being unable to separate without a wet sievee removal efciencies for the gravel washed by water
80 were similar (21 29% and 30 26%, respectively),101 showed an enhanced removal efciency (64 16%).se results show the biosurfactant SP101 is effective at
TPH removal efciency from gravel, which contradictson the inability of surfactants to improve the washingction .zing TPH concentration in all three major solid fractionsuent), we observed apparent differences in behav-two surfactants (Fig. 3). Specically, SP101 appearedive at moving contamination into the ne solid fraction
hereas, Tween80 was more effective at concentratingion into the efuent (Fig. 3d and 4). Given that the neon is typically disposed of to landll in soil washingncentrating contamination in this fraction seems less
144 A. Uhmann, T.J. Aspray / Journal of Hazardous Materials 219 220 (2012) 141 147
Fig. 2. Surfactant inuences on soil fraction and liquid efuent analyses.
important than the improved cleaning of gravel and sand fractionswhere stringent site remedial targets apply. The contaminant dis-tribution was different for the three wash solutions, but the purposeof soil washing, moving the contaminants from the gravel and sand,
was improved by the surfactant addition. In summary, SP101 wasmost effective at washing the gravel and sand fractions; with 6%contamination with SP101 in the gravel and sand, compared to 16%with Tween80 and 19% for water only (Fig. 4). Tween80 has alreadyFig. 3. TPH concentration in each fraction (n = 3); with and without compensation for surfactant inuen...