Presentation on theme: "EXPERIMENTAL STUDY AND MODELLING OF LINEAR ALKYLBENZENE SULPHONATE IN SAND AND SOIL Boluda-Botella N., Cases V., Gomis V., León V.M., and Soriano R. Chemical."— Presentation transcript:
EXPERIMENTAL STUDY AND MODELLING OF LINEAR ALKYLBENZENE 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 Alicante (Spain). Tel , ext Fax: INTRODUCTION 11th Mediterranean Congress of Chemical Engineering (EXPOQUIMIA) Barcelona, Spain October 21-24, 2008 MATERIALS AND METHODS Agricultural soil: Agricultural soil: CaCO 3 : 38.3%. Organic Carbon: 0.78% sand: 23.6%, silt: 38.0% and clay: 38.4% LAS Standard: LAS Standard: 12.1% C 10 LAS, 34.1% C 11 LAS, 30.6% C 12 LAS and 23.2% C 13 LAS, donated by PETRESA. Commercial Sand: Commercial Sand: Sea sand, purified (Merck) LAS Analysis: Samples injected in a HPLC. Stationary-phase:Lichrospher 10 m 100RP-8(25x0.46) Teknokroma Mobile phase: MeOH/H 2 O (85/15)+0.5M NaClO 4 ·H 2 O 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 . Additional details of specific LAS experiments are reported elsewhere [4,5]. REFERENCES  Jensen J., The Science of Total Environment, 226,  Verge C., Moreno A, Bravo J. and Berna J. L., Chemosphere, 44,  Gomis, V., Boluda, N. and Ruiz, F., J. Cont. Hydrol., 29,  Boluda N., León V. M., Prats D. and Chorro M.C., th Med. Congress of Chem. Eng. Experimental set-up: column experiments were performed in laboratory scale.  Boluda N., Cases, V., León, V.M., Gomis, V. and Prats, D., Hidrol. y aguas subt., 22. IGME. Spain.  Boluda Botella, N., Gomis, V. and Pedraza, R., st SWIM-SWICA. Cagliary (Italy).  Parkhurst, D.L. and Appelo, C.A.J., U.S. Geological Survey. Water Res. Inv. Report , 312 pp.  Tebes-Stevens, C., Valocchi A.J., VanBriesen J.M., Rittmann B.E., J. of Hydrol., v. 209, p 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 (C 10, C 11, C 12, C 13 ) 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 CaCl 2 as tracer) were obtained prior to the LAS desorption experiments. Hydrodynamic column parameters were obtained using ACUAINTRUSION , designed with Visual Basic 6.0 (Microsoft®). LAS DESORPTION EXPERIMENTS RESULTS REACTION PARAMETERS Convection-dispersion equation Adsorption affects the convection term Retardation FactorDistribution Coefficient Where: (velocity), (porosity), gr (density of grain) Obtained graphically with experimental results SIMULATION CURVES WITH PHREEQC CONCLUSIONS Tap water composition: Tap water composition: concentration of major ions (in table) The Linear distribution coefficient K d is considered to describe adsorption: Cads = K d 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 KdKd PHREEQC (Versión 2)  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.,  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: 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.