experimental study and modelling of linear alkylbenzene sulphonate in sand and soil boluda-botella...
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EXPERIMENTAL STUDY AND MODELLING OF LINEAR EXPERIMENTAL STUDY AND MODELLING OF LINEAR ALKYLBENZENE SULPHONATE IN SAND AND SOILALKYLBENZENE SULPHONATE IN SAND AND SOIL
Boluda-Botella N., Cases V., Gomis V., León V.M., and Soriano R. Chemical Engineering Department, University of Alicante. Apdo. 99, E-03080 Alicante (Spain). Tel.+34 965903400, ext.2647. Fax:+34 965903826.
E-mail: [email protected]
INTRODUCTIONINTRODUCTION
11th Mediterranean Congress of Chemical Engineering (EXPOQUIMIA) Barcelona, Spain October 21-24, 2008
MATERIALS AND METHODSMATERIALS AND METHODS
Agricultural soil:Agricultural soil: CaCO3: 38.3%. Organic Carbon: 0.78% sand: 23.6%, silt: 38.0% and clay: 38.4%
LAS Standard:LAS Standard: 12.1% C10LAS, 34.1% C11LAS, 30.6% C12LAS and 23.2% C13LAS, donated by PETRESA.
Commercial Sand:Commercial Sand: Sea sand, purified (Merck)
LAS Analysis: Samples injected in a HPLC. Stationary-phase:Lichrospher 10m 100RP-8(25x0.46) Teknokroma Mobile phase: MeOH/H2O (85/15)+0.5M NaClO4·H2O Flow: 0.8 mL/min . UV detector (254 nm)
Performed Column Experiments: Thermostated stainless steel column: 22.4cm length, 2.5cm internal diameter (25ºC). Column connected to a HPLC pump (Shimadzu LC 9A)
To study the physicochemical desorption of LAS, two laboratory experiments with columns containing 100 % sand (Test I) and 75% sand – 25 % soil (Test II) have been conducted. The experimental set-up consisted of a cylindrical stainless steel column filled with soil and connected to a HPLC pump [3]. Additional details of specific LAS experiments are reported elsewhere [4,5].
REFERENCESREFERENCES[1] Jensen J., 1999. The Science of Total Environment, 226, 93-111.[2] Verge C., Moreno A, Bravo J. and Berna J. L., 2001. Chemosphere, 44, 1749-1757.[3] Gomis, V., Boluda, N. and Ruiz, F., 1997. J. Cont. Hydrol., 29, 81-91.[4] Boluda N., León V. M., Prats D. and Chorro M.C., 2005. 10th Med. Congress of Chem. Eng.
Experimental set-up: column experiments were performed in laboratory scale.
[5] Boluda N., Cases, V., León, V.M., Gomis, V. and Prats, D., 2007. Hidrol. y aguas subt., 22. IGME. Spain.[6] Boluda Botella, N., Gomis, V. and Pedraza, R., 2006. 1st SWIM-SWICA. Cagliary (Italy). [7] Parkhurst, D.L. and Appelo, C.A.J., 1999. U.S. Geological Survey. Water Res. Inv. Report 99-4259, 312 pp.[8] Tebes-Stevens, C., Valocchi A.J., VanBriesen J.M., Rittmann B.E., 1998. J. of Hydrol., v. 209, p. 8-26.
Over the last two decades, many studies have been performed to characterize the environmental behaviour of linear alkylbenzene sulphonate (LAS), one of the major ingredients of synthetic detergents. In fact, the fate, effects, behaviour and sorption of LAS in different soils have established a good foundation for understanding its interactions [1-2]. However, few reports analyse how desorption processes occur. In recent years, high loads of treated wastewater or sludge, which can contain high concentrations of LAS, have been applied to agricultural areas, and therefore migration of these contaminants could affect groundwater quality.
A continuous 0.5 mL/min in-flow of filtered and sterilised tap water containing 5 ppm LAS was injected into both columns for several days until the concentration at the outlet was close to that of each homologue (C10, C11, C12, C13) injected. Formaldehyde was included to avoid growth of bacteria and hence microbiological biodegradation.
The desorption experiments started when tap water without LAS was injected, and the effluent was collected in small proportions, at first every 20 minutes/sample, and later every 100 minutes/sample.
LAS samples were analysed by HPLC using a UV detector (254 nm). Experimental results from sand columns showed that the concentration of different homologues, in general, decreases sharply within a relatively short time, whereas the experiment with sand and soil exhibited more dispersive spreading.
COLUMN TRANSPORT PARAMETERS
The experimental breakthrough curves (with CaCl2 as tracer) were obtained prior to the LAS desorption experiments. Hydrodynamic column parameters were obtained using ACUAINTRUSION [6], designed with Visual Basic 6.0 (Microsoft®).
LAS DESORPTION EXPERIMENTSLAS DESORPTION EXPERIMENTS
SAND COLUMN DESORPTION
0.0
0.2
0.4
0.6
0.8
1.0
1.2
0 10 20 30 40 50 60 70Time (h)
co
nc
en
tra
tio
n (
pp
m)
Sim C10LASExp C10LASSim C11LASExp C11LASSim C12LASExp C12LASSim C13LASExp C13LAS
75% SAND-25% SOIL COLUMN DESORPTION
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
0 50 100 150 200 250 300 350Time (h)
co
ncen
trati
on
(p
pm
)
Sim C10LASExp C10LASSim C11LASExp C11LASSim C12LASExp C12LASSim C13LASExp C13LAS
RESULTSRESULTS
REACTION PARAMETERS
Convection-dispersion equation
Ion concentration
(mg/L)
Test Ca2+ Na+ K+ Mg2+ Cl- SO42- HCO3
-
I 125 90 3.3 45 230 70 280
II 90 100 2.6 40 250 80 290
Test Porous medium
Q (mL/min)
u (cm/h)
tm (h)
Pe=vL/D
v=u/ (cm/h)
DL (cm2/h)
(cm)
I 100% sea
sand 0.50 5.71 1.78 156 0.45 12.6 1.82 0.144
II 75% sea
sand +25% soil
0.50 5.74 1.93 117 0.49 11.58 2.21 0.191
xC
x
CD
tC
2
2
xC
tC
dgr
K1
1
Adsorption affects the convection term Retardation Factor
dgrR K
11
Distribution Coefficient
Where: (velocity), (porosity), gr (density of grain)Obtained graphically with
experimental results
SIMULATION CURVES WITH PHREEQC
CONCLUSIONSCONCLUSIONS
Tap water composition: Tap water composition: concentration of major ions (in table)
The Linear distribution coefficient Kd is considered to describe adsorption: Cads = Kd C, where Cads is the sorbed concentration of a solute (moles/kg of solid) and C is the concentration in solution (moles/L of solution)
Determined in reactive transport experiment
Kd
PHREEQC (Versión 2) [7] is a computer program for one-dimensional reactive transport calculations designed by the U.S. Geological Survey. The user-friendly interface is useful for simulations of many practical problems in hydrogeochemistry.
LAS homologues are defined as SOLUTION_MASTER_SPECIES. Initial SOLUTION_SPECIES and initial sorbed species are quantified to start the simulation.
PHREEQC allows for several options in the simulation of surface reactions. However, in this case we defined kinetic sorption reaction for different species (no surface definitions are needed)
Tebes-Steven et al., [8] defined kinetic sorption for solution species by the rate equation:
where Ci is either LAS homologue (mol/L) and Cads their sorbed concentration (mol/kg sediment), Km is the transfer coefficient (hr-1) and Kd is the distribution coefficient (L/kg). The values of the coefficients are given in the following table:
d
adsimi
CCKR
K
Km (h-1) Kd (L/kg)
Test C10 C11 C12 C13 C10 C11 C12 C13
I 0.25 1 4 4 0.10 0.36 1.30 4.90
II 0.25 1 4 4 0.45 3.36 9.70 23.0
Two continuous LAS desorption experiments have been carried out in columns containing 100 % sand and 75% sand – 25 % soil. Experimental results from sand columns showed that the concentration of different homologues, in general, decreases sharply within a relatively short time, whereas the experiment with sand and soil exhibited more dispersive spreading. PHREEQC was applied in both cases assuming convective-dispersive transport and kinetic sorption reaction. Distribution coefficients, determined earlier using experimental data, are larger in tests employing soil (greater sorption). Transfer coefficients, which increase with homologue chain length, were kept constant during the two tests. Simulated results are in accord with experimental data. Calculated sorbed homologue concentrations are greater in tests employing soil and a longer desorption time is expected.
This graphical user interface calculates the best fit of the experimental data (chloride concentration (mmol/L) versus experimental time (h)) with the analytical solution of the convection-dispersion equation.
SAND COLUMN DESORPTION
0.E+00
2.E-09
4.E-09
6.E-09
8.E-09
1.E-08
1.E-08
0 10 20 30 40 50 60 70Time (h)
mo
l LA
S a
ds/
g s
ed
Sim C10LAS
Sim C11LAS
Sim C12LAS
Sim C13LAS
75 % SAND-25 % SOIL COLUMN DESORPTION
0.E+00
1.E-08
2.E-08
3.E-08
4.E-08
5.E-08
6.E-08
7.E-08
0 50 100 150 200 250 300 350Time (h)
mo
l LA
S a
ds/
g s
ed
Sim C10LAS
Sim C11LAS
Sim C12LAS
Sim C13LAS