Nonlinear Sorption Research Articles

Comparison of Naphthalene Diffusion and Nonequilibrium Adsorption-Desorption Experiments

Diffusion of hydrophobic organic compounds (HOC) is a key process controlling transport of contaminants in soils. However, the separate effects of sorption and diffusion on net (effective) HOC diffusion are not fully understood. In this study, effective diffusion of naphthalene in five unsaturated soils was evaluated by: (i) naphthalene adsorption-desorption experiments (batch method), (ii) naphthalene effective diffusion experiments (half-cell method), and (iii) trace-gas diffusivity experiments (chamber method). There was no soil type effect on gas diffusivity in repacked unsaturated soil, but a pronounced soil type effect on naphthalene sorption behavior. Varying degree of adsorption nonlinearity (Freundlich n' a ) and apparent adsorption-desorption nonsingularity (ω) and w increased with decreasing n' a were observed. In the half-cell experiments, gas diffusion was the governing naphthalene transport mechanism. Three effective diffusion coefficients were calculated from the half-cell experiments, based on concentration profile from either the whole (D eff ) cell, the source (desorption) half-cell (D eff,D ), or the recipient (adsorption) half-cell (D eff,A ). Generally, the observed D eff decreased with naphthalene-soil contact time, because of aging effects. The D eff , D eff,A , and D eff,D values (half-cell method) could only to some extend be estimated from Freundlich isotherm parameters (batch method). A suggested index of effective diffusion nonsingularity, H = D eff,D /D eff,A , showed that H was correlated with w and inversely correlated with n' a . Thus, the sorption nonlinearity (n' s ) was found to provide good indications of degree of nonsingularity in both HOC adsorption-desorption and effective diffusion. The combination of batch and half-cell experiments generally gave useful insight towards understanding and predicting the influence of sorption nonlinearity and nonequilibrium on HOC diffusion.

Comparison of fully coupled approaches for approximating nonlinear transport and reaction problems

The purpose of this work is to evaluate the computational efficiency of fully coupled approaches for approximating a common class of nonlinear, two-phase advective–dispersive–reactive equations. The general problem considered includes homogeneous phase chemical kinetics, equilibrium interphase mass transfer, and rate-controlled interphase mass transfer––all of which may be nonlinear. Aspects of the problem investigated include discrete mass conservative formulations, temporal discretization approaches, and nonlinear equation solution methods. Their effect on computational efficiency is investigated through a series of numerical experiments using a nondimensional model problem. The effect of problem characteristics such as large sorption capacity, strong sorption nonlinearity, fast mass transfer, fast reactions, and strong diffusion is investigated. Comparisons of solution efficiency show that the optimal approach depends upon: (1) the characteristics of the problem considered, which may be described in a nondimensional form; and (2) the accuracy achieved in the solution. Results offer general guidance for selecting solution approaches for the class of problems investigated and introduce some new solution approaches to the water resources field that may be applicable to other problems.

Comparison of Naphthalene Diffusion and Nonequilibrium Adsorption-Desorption Experiments

Diffusion of hydrophobic organic compounds (HOC) is a key process controlling transport of contaminants in soils. However, the separate effects of sorption and diffusion on net (effective) HOC diffusion are not fully understood. In this study, effective diffusion of naphthalene in five unsaturated soils was evaluated by: (i) naphthalene adsorption-desorption experiments (batch method), (ii) naphthalene effective diffusion experiments (half-cell method), and (iii) trace-gas diffusivity experiments (chamber method). There was no soil type effect on gas diffusivity in repacked unsaturated soil, but a pronounced soil type effect on naphthalene sorption behavior. Varying degree of adsorption nonlinearity (Freundlich n′a) and apparent adsorption-desorption nonsingularity (ω) and ω increased with decreasing n′a were observed. In the half-cell experiments, gas diffusion was the governing naphthalene transport mechanism. Three effective diffusion coefficients were calculated from the half-cell experiments, based on concentration profile from either the whole (Deff) cell, the source (desorption) half-cell (Deff,D), or the recipient (adsorption) half-cell (Deff,A). Generally, the observed Deff decreased with naphthalene-soil contact time, because of aging effects. The Deff, Deff,A, and Deff,D values (half-cell method) could only to some extend be estimated from Freundlich isotherm parameters (batch method). A suggested index of effective diffusion nonsingularity, H = Deff,D/Deff,A, showed that H was correlated with ω and inversely correlated with n′a Thus, the sorption nonlinearity (n′a) was found to provide good indications of degree of nonsingularity in both HOC adsorption-desorption and effective diffusion. The combination of batch and half-cell experiments generally gave useful insight towards understanding and predicting the influence of sorption nonlinearity and nonequilibrium on HOC diffusion.

The role of condensed organic matter in the nonlinear sorption of hydrophobic organic contaminants by a peat and sediments.

This study examines the effect of soil organic matter heterogeneity on equilibrium sorption and desorption of phenanthrene, naphthalene, 1,3,5-trichlorobenzene (1,3,5-TCB), and 1,2-dichlorobenzene (1,2-DCB) by soils and sediments. Two estuary sediments, a Pahokee peat (PP; Euic, hyperthermic Lithic Haplosaprist), and two subsamples (base- and acid-treated peat [TP] and acid-treated peat [FP]) of the peat were used as the sorbents. The contents of black carbon particles were quantified with a chemical extraction method. Petrographical examinations revealed the presence of the condensed soil and sediment organic matter (SOM) in Pahokee peat. The Freundlich isotherm model in two different forms was used to fit both sorption and desorption data. The results show that the sorption and desorption isotherms are generally nonlinear and that the apparent sorption-desorption hysteresis is present for phenanthrene and TCB. Detailed analysis of sorption data for the tested sorbent-sorbate systems indicates that black carbon is probably responsible for sorption isotherm nonlinearity for the two sediments, whereas the humic substances and kerogen may play the dominant role in nonlinear sorption by the peat. This investigation suggests that the microporosity of SOM is important for the hydrophobic organic contaminant (HOC) sorption capacity on the peat.

Solubility-normalized combined adsorption-partitioning sorption isotherms for organic pollutants.

Equilibrium sorption isotherms were measured for five different low-polarity organic compounds (benzene, trichloroethene, 1,2- and 1,4-dichlorobenzene, and phenanthrene) over a wide concentration range. The investigated sorbents can be grouped into the following three classes: (1) humic soil organic matter, which shows linear sorption isotherms (solely partitioning, as observed in the peat sample); (2) carbon materials, which were thermally altered (due to their natural history or industrial production) and thus contain a high specific surface area and exhibit nonlinear isotherms, and (3) pure engineered microporous materials (e.g., zeolites and activated carbon), where adsorption is solely due to a pore-filling process. Sorption of all compounds was fitted very well by the Polanyi-Dubinin-Manes (PDM) model, which for sorbents containing humic organic matter (e.g., peat) was combined with linear partitioning. Both the partitioning and the Polanyi-Dubinin-Manes model predict unique sorption isotherms of similar compounds if the solubility-normalized aqueous concentration is used. In addition, an inverse linear relationship between the distribution coefficient (Kd) and water solubility, which was very well confirmed by the data, is obtained. This also leads to unit-equivalent Freundlich sorption isotherms and explains the often observed apparent correlation between sorption capacity at a given concentration (e.g., Freundlich coefficient) and sorption nonlinearity (Freundlich exponent).

SORPTION AND TRANSPORT OF IRON-CYANIDE COMPLEXES IN UNCONTAMINATED SOIL INVESTIGATED IN COLUMN EXPERIMENTS

The occurrence of the iron-cyanide complexes ferrocyanide, [FeII(CN)6]4−, and ferricyanide, [FeIII(CN)6]3− in soil and groundwater is caused by disposal of industrial wastes and by the use of road salt containing ferrocyanide. We investigated the sorption and transport of iron-cyanide complexes in sandy uncontaminated soil (Ap horizon, Dystric Gleysol; 857 g sand kg−1, organic C 18 g kg−1, pH 5.8) in column experiments at saturated conditions and two concentrations, 0.03 and 10 m M [Fe(CN)6]. When using 10 m M, flow was interrupted for 36 h. Batch desorption experiments using phosphate and chloride were conducted to evaluate fractions of sorbed iron-cyanide complexes differing in their affinity for the soil matrix. Tracer breakthrough experiments using chloride indicated strongly advective flow in all experiments. The transport of both iron-cyanide complexes was characterized by rate-limited and nonlinear sorption affected by hysteresis. Rate-limited sorption was shown by the decrease of effluent concentrations after flow interruptions and by tailing. Nonlinear sorption became evident by the retardation of the breakthrough curves, depending on influent concentrations. Breakthrough of ferrocyanide took longer than that of ferricyanide, indicating stronger sorption of ferrocyanide. The extent of iron-cyanide complex desorption depended on (i) the amount of iron-cyanide complexes sorbed previously, (ii) the type of complex sorbed, and (iii) the solution used to desorb. For the experiment, higher amounts of iron-cyanide complexes sorbed resulted in lower desorption. More ferricyanide than ferrocyanide was desorbed, and phosphate desorbed more iron-cyanide complexes than chloride. Precipitation of iron-cyanide complexes following desorption experiments was indicated by the presence of blue precipitates in the soil matrix. Consequently, the sorption behavior of iron-cyanide complexes in uncontaminated soil was complex due to rate-limited and nonlinear sorption and precipitation. The experiments revealed that soils may act as a sink for iron-cyanide complexes at low concentrations, e.g., those originating from the use of road salt or occurring in contaminated seepage and groundwater. However, the long-term behavior of iron-cyanide complexes in this soil is characterized by continuous desorption.

Sensitivity analysis of physical and chemical properties affecting field-scale cadmium transport in a heterogeneous soil profile

Field-scale transport of reactive solutes depends on spatially variable physical and chemical soil properties. The quantitative importance of physical and chemical parameters required for the prediction of the field-scale solute flux is generally unknown. A sensitivity analysis is presented that ranks the importance of spatially variable water flow and solute transport parameters affecting field-scale cadmium flux in a layered sandy soil. In a Monte-Carlo simulation approach, partial rank correlation coefficients were calculated between model parameters and cadmium flux concentrations at various time steps. Data on the heterogeneity of flow and transport parameters were obtained from a 180 m-long and 1 m-deep Spodosol transect. Each soil layer was described in terms of probability density functions of five model parameters: two shape parameters of van Genuchten's water retention curve, saturated hydraulic conductivity, dispersivity and soil–water distribution coefficient. The results showed that the cadmium flux concentrations at the bottom of the soil profile were most sensitive to the cadmium deposition rate and the soil–water distribution coefficient of all soil horizons. The maximum cadmium flux concentrations were also affected by variations in hydraulic conductivity of the humic topsoil horizons. Variations in shape parameters of the water retention curve did not significantly affect the field-scale cadmium flux. Variations in the dispersivity of the subsoil significantly influenced the early time cadmium concentrations. Monte-Carlo simulations involving non-linear sorption showed that cadmium flux concentrations were dominated by variations in the sorption constant and in the exponent of the Freundlich isotherm.

Long-term tillage effects on soil metolachlor sorption and desorption behavior.

Sorption and desorption are two important processes that influence the amount of pesticides retained by soils. However, the detailed sorption mechanisms as influenced by soil tillage management are unclear. This study examined the sorption and desorption characteristics of metolachlor [2-chloro-N-(2-ethyl-6-methyphenyl)-N-(2-methoxy-1-methylethyl)-acetamide] using the soil samples collected from the long-term conservation tillage (CnT) and conventional tillage (CT) research plots established in 1979 in Darlinton, SC. Humic acid (HA) and humin were extracted from the soils and used in the sorption experiments along with the whole soil samples. The sorption experiments were conducted using a batch-equilibration method. Three sequential desorption rinses were carried out following the sorption experiments. By comparing metolachlor sorption and desorption results we observed hysteresis for all soil samples and their organic matter fractions. Sorption nonlinearity (N) and hysteresis were dependent on the structure and composition of soil organic matter (SOM), e.g., Freundlich isotherm exponents (N) of HA and humin from CnT were higher than those of CT treatment, which may be related to high aromaticity of SOM fractions in CT treatment. Sorption capacity (K'f) was positively correlated with soil organic carbon (SOC) content. These results show that long-term tillage management can greatly affect metolachlor sorption and desorption behavior probably by qualitative differences in the structural characteristics of the humic substances.

Comment on “Model coupling intra-particle diffusion/sorption, nonlinear sorption, and biodegradation process” by H.K. Karapanagioti, C.M. Gossard, K.A. Strevett, R.L. Kolar, and D.A. Sabatini

Comment on “Model coupling intra-particle diffusion/sorption, nonlinear sorption, and biodegradation process” by H.K. Karapanagioti, C.M. Gossard, K.A. Strevett, R.L. Kolar, and D.A. Sabatini

Reply to comment on “Model coupling intraparticle diffusion/sorption, nonlinear sorption, and biodegradation processes” by H. Basagaoglu, T.R. Ginn, and B.J. McCoy

Reply to comment on “Model coupling intraparticle diffusion/sorption, nonlinear sorption, and biodegradation processes” by H. Basagaoglu, T.R. Ginn, and B.J. McCoy

Tracer and radionuclide sorption to vitric tuffs of Busted Butte, Nevada

Field-scale unsaturated-zone tracer tests have been performed at Busted Butte, Nevada, near the potential high-level radioactive waste repository at Yucca Mountain. These tests are intended to improve our understanding of unsaturated-zone transport processes, and to test our ability to predict field-scale behavior using laboratory-scale measurements. The field tests use a mixture of nonreactive and reactive tracers. Nonreactive tracers include Br −, I −, 5 different fluorobenzoic acids, Na fluorescein, and a pyridone derivative. Reactive tracers include the metals Li, Mn, Co, and Ni, and the organic dye rhodamine WT. Rock samples from 3 different stratigraphic units at the Busted Butte test facility have been extensively characterized lithologically and mineralogically, and analyzed for Fe and Mn oxide content. Sorption of Np, Pu, Am and the field tracers onto these 3 rocks has been measured using batch techniques. Results confirm that the nonreactive tracers are indeed nonreactive, and show that sorption of radionuclides and sorbing tracers increases with increasing degree of rock alteration, as evidenced by increasing levels of smectite and Fe and Mn oxides. Among the radionuclides, Am and Pu sorb much more strongly than Np; the tracers' degree of sorption is rhodamine WTLi⪡Mn<Ni<Co. Pu, Co, Mn, Ni and rhodamine WT exhibits strongly nonlinear sorption; Mn and Ni behavior may reflect competition with Co for sorption sites.

Immobilizing Humic Acid in a Sol−Gel Matrix: A New Tool To Study Humic-Contaminants Sorption Interactions

Humic substances originated from aquatic, soil, or sediment environments are mixtures of humic compounds with various characteristics. Sorption interactions with isolated, well defined humic fractions can be studied either in an aqueous phase ("dissolved humic substances"), or in a solid-phase, by coating mineral particles with the humic materials, or simply by working with humic acid particles (powder) at low pH to minimize dissolution. Each attitude, by definition, can be studied by different experimental techniques and has a different meaning for understanding natural environmental processes. In this study, a new tool for studying sorption interactions is presented. Sol-gel was used as an inert matrix to immobilize (entrap) various humic acids (HAs), and then used to study the interactions of several polycyclic aromatic hydrocarbons (PAHs) with the entrapped HA. Linear and nonlinear sorption coefficients were highly correlated with contaminant hydrophobicity. Sorption of pyrene to immobilized HA was in the order of soil HA > Aldrich HA approximately = peat HA. It was concluded that the entrapped HAs retained their original properties in the gel matrix and were accessible to the external contaminant through the pore network. Additionally, binding coefficients of pyreneto dissolved humic substances and to dissolved organic matter (DOM) were determined from the reduction in pyrene sorption to immobilized HA in the presence of dissolved humic material or DOM in solution. Binding coefficients of pyrene were in the order of the following: dissolved Aldrich HA > dissolved peat fulvic acid (FA) > DOM derived from mature compost > DOM derived from fresh compost.

Comment on “Solute transport under non-linear sorption and decay” by Sergio E. Serrano

Reference ECOL-ARTICLE-2002-014doi:10.1016/S0043-1354(01)00545-0 URL: http://www.elsevier.com/wps/find/journaldescription.cws_home/309/description#description Record created on 2005-12-09, modified on 2016-08-08

Reply to Comment on “Solute transport under non-linear sorption and decay”

Reply to Comment on “Solute transport under non-linear sorption and decay”

Sorption of bentazone, dichlorprop, MCPA, and propiconazole in reference soils from Norway.

Sorption-desorption kinetic and isotherm studies were performed by the batch equilibrium technique in three Norwegian soils. The soils were a fine sandy loam, a loam, and a soil of highly decomposed organic material. Two commercially formulations were used, Triagran-P and Tilt, containing either a mixture of bentazone [3-isopropyl-1H-2, 1,3-benzothiadiazin-4(3H)-one 2,2-dioxide], dichlorprop [(R)-2-(2, 4-dichlorophenoxy)-propionic acid], and MCPA [(4-chloro-2-methylphenoxy)acetic acid], or propiconazole [(+/-)1-(2-(2,4-dichlorophenyl)-4-propyl-1,3-dioxolan-2-ylmethyl)-1H-1,2,4-triazole] alone. Sorption-desorption equilibrium occurred within 10 h for all pesticides. The Freundlich isotherms indicated nonlinear sorption of bentazone, dichlorprop, MCPA, and propiconazole. For all pesticides the highest Freundlich adsorption coefficient (K(F)) values were in the soil with highest organic content and lowest pH. For the fine sandy loam and loam, which are representative Norwegian agricultural soils, the results indicate that bentazone, dichlorprop, and MCPA are mobile with KF values ranging from 0.07 to 1.50 mg1-1/n kg(-1) L1/n. Propiconazole is much less mobile with KF values ranging from 27.00 to 36.02 mg1-1/n kg(-1) L1/n in the agricultural soils.

Role of pH in partitioning and cation exchange of aromatic amines on water-saturated soils

Predicting the reversible interactions between aromatic amines and soil is essential for assessing the mobility, bioavailability and exposure from contaminated sites. Reversible sorption mechanisms of aniline and α-naphthylamine were investigated by using single and binary solute sorption to five soils at several pH values, and by applying a distributed parameter (DP) model. The DP model assumes linear partitioning of the neutral species into soil organic matter domains and organic cation binding on negative-charged sites with the exchange coefficients represented by a Gaussian probability distribution. Sorption nonlinearity was attributed to cation exchange with varying site affinities, which was adequately simulated using the DP model. Greater uptake by hydrophobic partitioning and selectivity for cation exchange sites was observed for α-naphthylamine compared to aniline. Sorption of α-naphthylamine was not impacted quantitatively by aniline under those conditions examined; however, aniline sorption was reduced by α-naphthylamine with the largest reduction occurring in the soil with the lowest pH. DP model simulations showed that although hydrophobic partitioning increases with soil–solution pH, cation exchange still contributes significantly to the total sorption even at soil–solution pH values greater than p K a+2.

Permeation Time Lag and the Concentration Dependence of the Diffusion Coefficient of CO2 in a Carbon Molecular Sieve Membrane

The CO2 permeation experiments were performed on a microporous carbon molecular sieve membrane (CMSM) at 25 °C and over a wide pressure range. The permeation time lag of the penetrant was employed to study the concentration dependence of the diffusion coefficient. The analytical solutions are derived for permeation systems with a nonlinear sorption isotherm (Langmuir) and a concentration-dependent diffusivity [with the functional form of Dμ(c) = 1/(1 − θ)n, where θ is the ratio of surface coverage and n ≥ 1]. By comparison of the experimental data with the theoretical models, it is found that, in this CMSM, the apparent diffusivity of CO2 takes a concentration dependence stronger than that described by the traditional HIO model [i.e., Dμ(c)/ = 1/(1 − θ)].

Isotope effects in α-PdH(D) as an instrument for diagnosing bulk defects

Protium and deuterium sorption in the α-phase region is studied for highly defective palladium electrodeposits fabricated under controllable potentiostatic modes, particularly in the region of concentrated hydride formation. An anomalously high hydrogen content is observed for these samples in both α- and β-hydrides. On the basis of coulometry in the course of anodic hydrogen extraction, the non-linear sorption isotherms are plotted and their specific features are considered under an assumption of simultaneous equilibrium sorption of hydrogen by several types of lattice positions with a certain degree of defectiveness. Less defective palladium samples deposited in the absence of bulk hydridization are studied for comparison. The approach is proposed to estimate the fraction of defective regions. The procedure of analyzing the low-pressure limit is used for the first time for determining the specific values of the isotope effect, and also H and D Sievert's constants. The isotope effect is demonstrated to be extremely sensitive to the type of defectiveness.

Solute transport under non-linear sorption and decay

Contaminant transport in aquifers is usually represented by a solution to the advective–dispersive differential equation. When the contaminant is subject to non-linear degradation or decay, or it is characterized by a chemical constituent that follows a non-linear sorption isotherm, the resulting differential equation is non-linear. Using the method of decomposition, series solutions were obtained for the non-linear equation. The series were used to derive and test “simulant” solutions that arise using the concept of double decomposition. Simulant solutions are closed-form analytic expressions that approximate part of the series. These expressions are simple, stable, and flexible. They permit an accurate forecasting of contaminant propagation under non-linearity in laboratory or field investigations at early or prolonged times after the spill. In this article, the practical scenario of an instantaneous spill, and that of a constant concentration boundary condition, is studied for situations of non-linear decay, non-linear Freundlich isotherm, and non-linear Langmuir isotherm. The solutions are verified with limited well-known analytical solutions of the linear reactive and non-reactive equations with excellent agreement, and with limited finite difference solutions. Plumes undergoing non-linear decay experience a profile re-scaling with respect to that of linear decay, the degree of which is controlled by the magnitude of the non-linear parameter b. The direction of the scaling (scaling up or scaling down with respect to the linear decay plume) is controlled by the magnitude of C (whether greater or less than 1) in relation to the magnitude of b (whether greater or less than 1). When C>1, values of b<1 produce plumes that experience less decay (i.e., are scaled up) than that of the linear decay, whereas values of b>1 produce non-linear plumes that experience more decay (i.e., are scaled down) than that of the linear decay. The opposite effect is observed when concentrations are less than 1. In other words, when C<1, values of b<1 produce non-linear plumes that experience more decay (i.e., are scaled down) than that of the linear decay, whereas values of b>1, produce non-linear plumes that experience less decay (i.e., are scaled up) than that of the linear decay. A plume undergoing non-linear sorption according to a Freundlich isotherm retards the processes of advection and dispersion with respect to a plume with no sorption. Similar to the case of non-linear decay, whether this retardation is more or less pronounced than that of the linear sorption plume depends on whether the values of b and C are greater or less than 1. The solution presented here for the advective dispersive equation subject to a Freundlich sorption isotherm is restricted to concentration greater than 1. When C>1 and b<1, the decrease in mobility in the non-linear plume is not as pronounced as that of a plume modeled by a linear isotherm. Plume shape may be quite sensitive to the values of the non-linear parameters. Plumes with parameter values b<1 (and C>1) exhibit the well-known lack of symmetry with respect to their center of mass, sharp fronts, and the tailing effects observed at hazardous waste sites. As the magnitude of the non-linear parameter increases, the non-linear plume approaches the linear one. This partial non-linear “retardation” can now be observed quantitatively with the models presented herein. The models developed also simulate the case of b >1 (i.e., “unfavorable” sorption), which produce a plume even more retarded than the linear. The shape of a contaminant plume following a non-linear Langmuir isotherm is very sensitive to the magnitude of the non-linear parameter α. Approximate solutions for mild non-linearity are presented.

Model coupling intraparticle diffusion/sorption, nonlinear sorption, and biodegradation processes

Diffusion, sorption and biodegradation are key processes impacting the efficiency of natural attenuation. While each process has been studied individually, limited information exists on the kinetic coupling of these processes. In this paper, a model is presented that couples nonlinear and nonequilibrium sorption (intraparticle diffusion) with biodegradation kinetics. Initially, these processes are studied independently (i.e., intraparticle diffusion, nonlinear sorption and biodegradation), with appropriate parameters determined from these independent studies. Then, the coupled processes are studied, with an initial data set used to determine biodegradation constants that were subsequently used to successfully predict the behavior of a second data set. The validated model is then used to conduct a sensitivity analysis, which reveals conditions where biodegradation becomes desorption rate-limited. If the chemical is not pre-equilibrated with the soil prior to the onset of biodegradation, then fast sorption will reduce aqueous concentrations and thus biodegradation rates. Another sensitivity analysis demonstrates the importance of including nonlinear sorption in a coupled diffusion/sorption and biodegradation model. While predictions based on linear sorption isotherms agree well with solution concentrations, for the conditions evaluated this approach overestimates the percentage of contaminant biodegraded by as much as 50%. This research demonstrates that nonlinear sorption should be coupled with diffusion/sorption and biodegradation models in order to accurately predict bioremediation and natural attenuation processes. To our knowledge this study is unique in studying nonlinear sorption coupled with intraparticle diffusion and biodegradation kinetics with natural media.