Freundlich Sorption Isotherm Research Articles

Long-term sewage sludge application and wastewater irrigation on the mineralization and sorption of 17β-estradiol and testosterone in soils

The disposal of animal manures, wastewater and sewage sludge to agricultural land can lead to the transfer of steroid hormones like 17beta-estradiol and testosterone into soils, surface and groundwaters. The objective of this study was to investigate the effects of different site histories like wastewater irrigation and sewage sludge application on hormone mineralization and sorption in soils. Two agricultural sites with different long-term treatment histories with wastewater and sewage sludge were sampled. The mineralization of (14)C-17beta-estradiol and (14)C-testosterone was studied during incubations at 20 degrees C over three weeks. Despite the structural resemblance of both hormones the mineralization rate of 17beta-estradiol was about an order of magnitude lower than that of testosterone in all four soils, reaching 5-7% vs. 50-59%, respectively. Estradiol mineralization was significantly lower in soils with long-term wastewater irrigation than in the corresponding soil with freshwater irrigation. Pre-incubation of the soils with unlabeled hormones or application of the hormones within a wastewater matrix had only minor effects on their mineralization. The results indicate that estradiol mineralization occurs co-metabolically and is limited by sorption, whereas testosterone appears to be utilized directly by soil microorganisms. Sorption of (14)C-17beta-estradiol and (14)C-testosterone to sterile and unsterile soils was determined in batch experiments with CaCl(2) or wastewater solution with hormone concentrations of 0.13-0.0013 mug mg(-1). FREUNDLICH sorption isotherms and parameters like K(F) and log K(oc) values were used to describe the results. The K(F) values for estradiol sorption were generally about 1.2 to 1.6-fold higher than for testosterone. The SOC-normalized partition coefficients K(oc) also differ accordingly and indicate quite large differences in soil organic matter qualities relating to hormone sorption between the soils and treatments. When the hormones were added to the soil within a wastewater matrix less estradiol was sorbed in the solid phase than in the controls with pure water, thus indicating that wastewater contains soluble sorbents.

Determination of Microbial Sorption Isotherms from Column Experiments

Microbial sorption isotherms cannot be obtained using the traditional batch methods owing to the difficulty of distinguishing between reversible and irreversible sorption. In this research, we investigated microbial sorption isotherms of Pseudomonas fluorescens, Pseudomonas putida, and Pseudomonas sp. on an alluvial loam from the Central Oklahoma Aquifer (COA) using column experiments. All these three bacterial strains displayed a concave isotherm on COA, which can be described by the Freundlich sorption isotherms. We explained the concave‐shaped microbial sorption isotherms using the surface thermodynamic theory. In this study, we also investigated the impact of transport velocity on the microbial breakthrough curves. We found that the same bacterial strain had the same sorption isotherms but different deposition coefficient at different flow rates. The high solid to solution ratio of column experiments is close to that which is encountered in the natural systems, which makes this method a useful tool for guidance of in‐situ bioremediation.

Sorption of cesium on granite under aerobic and anaerobic conditions

This study focused on the determination of distribution coefficients (K d) of 137Cs under aerobic (∼21% O2) and anaerobic conditions (1−10 ppm O2) which might be found in the deep geologic environment. The anaerobic conditions were simulated in a glove box filled with highly pure argon (99.9%). Both batch tests and solid-phase analyses, including X-ray diffraction, N2-BET surface area, and polar-microscopy/autoradiography were employed for analyzing the sorption of 137Cs on granite, which is the potential host rock for waste disposal in Taiwan. Before starting batch tests, the rock samples were placed in the glove box for one week, and the E h values of experimental liquids were periodically measured until the E h value decreased below 0 mV. The sorption of 137Cs was studied at various concentrations in synthetic groundwater. The Freundlich sorption isotherm seems to be adequate to quantitatively describe the sorption of Cs for the concentration ranges (i.e., 10-3−10-6 M) conducted in both conditions. The distribution coefficient (K) obtained from the two-week batch tests indicated no obvious difference in two systems and the values of K and n are similar. In addition, sorption onto a specific host rock was found to be dependent on its mineralogical components. The photos obtained from polar-microscopy/autoradiography analyses showed that biotite is the principal mineral component responsible for the sorption of 137Cs onto granite.

Adsorption-desorption of HCH and Endosulfan on a Soil

Sorption – desorption of HCH (1,2,3,4,5,6 – Hexachlorocyclohexane) and Endosulfan (1,2,3,4,7,7 – Hexachlorobicyclo [2,2,1] – 2 – heptene – 5,6 – bisoxy methylene sulfite) on soil was studied using the batch equilibration technique with initial concentrations for the two chemicals ranging from 0.03 to 340 μg ml−1, which corresponds to a field application rate of 0.1 – 2.0 kg m−2. Calculated slopes of the Freundlich sorption isotherms were near to 1. The Kf, Kd, and Koc values determined for endosulfan were at least an order of magnitude greater than that determined for HCH. Kf values were 209 and 8035 for HCH and Endosulfan respectively. Hysteresis was observed for desorption of both the chemicals. Studies showed that Endosulfan and HCH binding to soil was strong and desorption cannot be predicted from adsorption isotherms only.

Sorption potential of rice husk for the removal of 2,4-dichlorophenol from aqueous solutions: Kinetic and thermodynamic investigations

The sorption potential of chemically and thermally treated rice husk (RHT) for the removal of 2,4-dichlorophenol (DCP) from aqueous solutions has been investigated. Sorption of DCP by rice husk was observed over a wide pH range of 1–10. The effect of contact time between liquid and solid phases, sorbent dose, pH, concentration of sorbate and temperature on the sorption of DCP onto rice husk has been studied. The pore area and average pore diameter of RHT by BET method are calculated to be 17 ± 0.6 m 2 g −1 and 51.3 ± 1.5 nm, respectively. Maximum sorption (98 ± 1.2%) was achieved for RHT from 6.1 × 10 −5 mol dm −3 of sorbate solution using 0.1 g of rice husk for 10 min agitation time at pH 6 and 303 K, which is comparable to activated carbon commercial (ACC) 96.6 ± 1.2%, but significantly higher than chemically treated rice husk (RHCT) 65 ± 1.6% and rice husk untreated (RHUT) 41 ± 2.3%. The sorption data obtained at optimized conditions was subjected to Freundlich, Langmuir and Dubinin–Radushkevich (D–R) isotherms. Sorption intensity 1/ n (0.31 ± 0.01) and sorption capacity multilayer C m (12.0 ± 1.6 mmol g −1) have been evaluated using Freundlich sorption isotherm, whereas the values of sorption capacity monolayer Q (0.96 ± 0.03 mmol g −1) and binding energy, b, (4.5 ± 1.0) × 10 4 dm 3 mol −1 have been estimated by Langmuir isotherm. The Langmuir constant, b, was also used to calculate the dimensionless factor, R L, in the concentration range (0.6–6.1) × 10 −4 mol dm −3, suggesting greater sorption at low concentration. D–R sorption isotherm was employed to calculate sorption capacity X m (2.5 ± 0.07 mmolg −1) and sorption energy E (14.7 ± 0.13 kJ mol −1). Lagergren and Morris–Weber equations were employed to study kinetics of sorption process using 0.2 g of RHT, 25 cm 3 of 0.61 × 10 −4 mol dm −3 sorbate concentration at pH 6, giving values of first-order rate constant, k, and rate constant of intraparticle transport, R id, (0.48 ± 0.04 min −1 and 6.8 ± 0.8 nmolg −1 min − 1 / 2 , respectively) at 0.61 × 10 −4 mol dm −3 solution concentration of DCP, 0.1 g RHT, pH 6 and 2–10 min of agitation time. For thermodynamic studies, sorption potential was examined over temperature range 283–323 K by employing 6.1 × 10 −4 mol dm −3 solution concentration of DCP, 0.1 g RHT at pH 6 and 10 min of agitation time and values of Δ H (−25 ± 1 kJ mol −1), Δ S (−61 ± 4 J mol −1 K −1) and Δ G 303K (−7.1 ± 0.09 kJ mol −1) were computed. The negative values of enthalpy, entropy, and free energy suggest that the sorption is exothermic, stable, and spontaneous in nature.

The influence of the rigidity of geosorbent organic matter on non-ideal sorption behaviors of chlorinated benzenes

This study focused on evaluating the influence of the rigidity of natural organic matter (NOM) associated with four natural geosorbents in controlling the non-ideal sorption behaviors of five chlorinated benzenes. Single solute sorption isotherms for each sorbate/sorbent combination were modeled and interpreted by the Freundlich sorption isotherm and the adsorption-partitioning model based on Polanyi–Manes theory (PM model). “Rigid” organic matter was operationally quantified as the fraction of carbon resistant to wet chemical oxidation (hard carbon) or thermal oxidation (soot carbon); atomic H/O ratios indicated a close correlation between the degree of reduction of the NOM and its rigidity. Sorbents with larger rigid carbon fractions had more non-linear sorption isotherms and higher organic carbon (OC) normalized sorption affinities. The size of the PM hole filling domain for a given sorbent was closely correlated with the extent to which the sorbent's affinity for chlorobenzenes exceeded predictions from a linear free energy relationship. Loss of some portions of the rigid character of the NOM domain due to the penetration of sorbate molecules (plasticization) was discussed as a possible contributor to the non-ideal sorption behaviors observed in this study. The existence of a permanently rigid NOM domain, not subject to plasticization under environmental conditions, was postulated as an additional factor determining the observed sorption behavior.

Sorption of HOC in soils with carbonaceous contamination: Influence of organic‐matter composition

AbstractDetailed information about structure and composition of organic sorbents is required to understand their impact on sorption capacity and sorption kinetic of organic pollutants. Therefore, the chemical composition of organic material from 18 geosorbents was investigated by solid‐state 13C nuclear‐magnetic‐resonance (NMR) spectroscopy. Structural parameters such as aromaticity, polarity, and alkyl‐C content were related to the Freundlich sorption exponent (1/n) and the sorption coefficient $ K_{OC}^\circ $. The geosorbents included three natural and four combusted coals (carbonaceous material), three Histosols, five mineral soils from Germany containing inputs of technogenic carbonaceous material, derived from industrial activities, and four non‐contaminated mineral soils from Germany. Equilibrium sorption was measured for five hydrophobic organic compounds and analyzed with the solubility‐normalized Freundlich sorption isotherm. With increasing maturation degree, the proportion of polar constituents decreases from the natural soils to the coals. In contrast to the non‐polluted mineral soils, the soils with technogenic input are characterized by high aromaticity and low polarity. A positive correlation between sorption coefficient $ K_{OC}^\circ $ and aromaticity was found. The Freundlich exponent (1/n) is negatively correlated with the aromaticity, denoting an increase of adsorption processes with increasing aromaticity. Likewise, the contribution of partitioning decreases. This sorption mechanism predominates only if the organic matter in the samples contains a high proportion of polar compounds.

Equilibrium Approaches to Organic Contaminant Transport Modeling in a Multiphase Groundwater System

Mathematical models were developed in this study based on equilibrium sorption approaches to simulate transport and retardation of organic contaminants such as polycyclic aromatic hydrocarbons in a multi-phase groundwater system. In a model development, the Langmuir or Freundlich sorption isotherms were incorporated into a retardation factor to account for nonlinear sorption of contaminants and colloids on solid matrix. Numerical solutions of model equations were obtained using a fully implicit finite difference method. Simulation results showed that the contaminant retardation factor varied temporally and spatially in a multi-phase system (dissolved phase, solid phase, and two mobile colloidal phases). Simulation also indicated that colloidal concentration and mobility would be key factors in controlling the contaminant transport in a multi-phase system. Sensitivity analysis demonstrated that the models were sensitive to changes of nonlinear isotherm coefficients and equilibrium distribution coefficients.

Adsorption of anionic dyes on aluminium treated corn cobs powder

Untreated textile effluents are highly toxic as they contain a large number of metal complex dyes. The effluents discharged from various textile and dyeing industries are hazardous coloured effluents. The uptake of anionic dyes by aluminium treated corn cobs powder have been studied by hatch technique. Maximum adsorption of dyes was observed at low adsorbate concentration, acidic pH and 30° temperature. The adsorption process follows Freundlich sorption isotherm and the process was found to he exothermic as adsorption decreases with increasing temperature.

Potassium hexacyanocobalt ferrate and ammonium molybdophosphate sorption bags for the removal of 137Cs from aqueous solutions and a simulated waste

AbstractIn the present study, the removal and immobilization of 137Cs from aqueous waste solutions and a simulated waste was investigated. Two inorganic ion‐exchange complexes: di‐potassium hexacyanocobalt(II)‐ferrate(II), K2CoFe(CN)6·xH2O (KCFC), and ammonium‐12‐molybdophosphate [(NH4)3PMo12O40·aq] (AMP), were charged separately into porous nylon bags (sorption bags) of 5 µm pore diameter. The first complex (KCFC) was prepared in our laboratory. The second (AMP) was used for comparison. Easy handling and increased potential for reuse characterize the sorption bag technique. The KCFC complex was investigated by thermal gravimetric analysis (TGA) and differential thermal analysis (DTA), porosity, infra‐red (IR) and X‐ray powder diffraction (XRD). The chemical and structural investigations revealed that the KCFC complex has adequate ion‐exchange capacity and high affinity for 137Cs. The sorption bag technique showed promising results for the removal of 137Cs from aqueous waste solutions. The KCFC bags showed the highest 137Cs removal (∼0.91 g g−1), at pH 8.5; AMP bags gave the highest 137Cs removal (∼0.97 g g−1) in 0.1 N HNO3 and 1.5 N HNO3, both with a waste: sorbent ratio of 80 cm3 g−1. Sorption data for both KCFC and AMP revealed a good fit to the Freundlich sorption isotherm. To assess the potential of sorption bags, the used bags were regenerated in different leachants and reused in further sorption investigations. 137Cs recovery from the used sorbents was ∼0.46 g g−1 using 6 N HCl as leachant for AMP, compared with ∼0.253 g g−1 for KCFC using 6 N NaCl. These results indicated stronger cesium immobilization in the KCFC complex. Copyright © 2003 Society of Chemical Industry

Propagation of nonlinear reactive contaminants in porous media

A study on the effect of nonlinear reactions on the space and time distribution of contaminant plumes governed by the advective‐dispersive equation in porous media was conducted. Several models of nonlinear reactions were considered: the irreversible nonlinear first‐order kinetic sorption model, the nonlinear Freundlich sorption isotherm model, the nonlinear Langmuir sorption isotherm model, and the reversible nonlinear kinetic sorption model. Each of these models was coupled with the advective‐dispersive equation with dimensionless concentration and an approximate analytical series solutions was obtained. Comparison between linear and nonlinear plumes indicated that nonlinear reactions may have a significant effect on the shape and spatial distribution of a contaminant at a given time and in certain cases may explain quantitatively the occurrence of scaled (e.g., concentration change while preserving shape), retarded, and nonsymmetric plumes as well as the presence of back tails and sharp front ends usually observed in the field. By adopting a nonlinear model of contaminant migration a more realistic representation of contaminant propagation is possible than that obtained with a linear model.

Atrazine sorption on surface soils: time-dependent phase distribution and apparent desorption hysteresis

Non-equilibrium sorption–desorption behavior of atrazine was studied on two surface soils. Impact of sorption contact time was evaluated by interpreting temporal variations in Freundlich sorption isotherm parameters n( t) and K F( t) obtained from the phase distribution relationships. The extent of sorption linearity was very similar ( n∼0.90) for the two soils at all sorption contact times. K F( t) increased with contact time and stabilized upon reaching apparent equilibrium. K F for woodland soil was significantly higher than that for agricultural soil. The Apparent Hysteresis Index (AHI) parameter was used to quantify sorption–desorption hysteresis arising from non-equilibrium sorption. AHI was a function of the sorption contact time and correlated well with K F( t). The woodland soil sorbed more herbicide due to its higher organic matter content. However, a larger fraction of the herbicide sorbed to this soil was released rapidly (within 24 h) following sorptive uptake. The differences in sorption–desorption behavior of atrazine in the two soils appear to be related to variations in the type and location of organic matter in the two soils. The parameters K F( t) and AHI( t) consistently demonstrated the effects that arise when batch systems are not brought to equilibrium during sorption studies.

MAGNETIC SORBENT FOR SOIL REMEDIATION—A WASTE FOR WASTE TREATMENT

The possibility of decontaminating arable soil, forest soil, and gley soil, artificially contaminated by solutions of cesium-137, strontium-85, and europium-152, by contact in common suspension with magnetic residues of leached nickel ores (SOR) from the former Sered hydrometallurgical plant and its magnetic separation was demonstrated. More than 60–98% of cesium and strontium took part in the exchange between the soil and the magnetic sorbent and could be efficiently removed at sorbent mass to soil mass ratio as large as 5. Freundlich sorption isotherms were used for the evaluation of the driving forces of the transfer process. Actual soil remediation depends on the possibility of recycling used SOR: the speciation of sorbate indicates that the retention of strontium takes place in an exchangeable form but that of cesium and europium manifests through a more strong binding to the oxide component of SOR.

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 thermodynamic behavior of zinc(II)-thiocyanate complexes onto polyurethane foam from acidic solutions

The uptake of Zn(II)-SCN complex onto polyurethane foam (PUF) has been investigated in detail with respect to different composition and variable concentration of electrolyte, zinc, thiocyanate ions and PUF, and equilibration time. The sorption data followed both Langmuir and Dubinin-Radushkevich (D-R) sorption isotherms over the entire concentration range of zinc investigated whereas Freundlich sorption isotherm is obeyed upto 13.6.10-3M concentration. The Langmuir constants Q = 202±7 mmole.g-1 and of b = (1.78±0.31.104 dm3.mole-1 and of D-R paraneter X m = 493±1 mmole.g-1, b = activity coefficient = -0.028±0.0002 and of sorption energy E = 13.2±0.5 kJ.mole-1 and Freundlich constants 1/n = 0.42±0.03 and c m = 6.47±1.7 mmole.g-1 were evaluated. The influence of temperature variation on sorption have yielded DH = -77.5±2.9 kJ.mole-1, DS = -5±0.09 J.mole-1.K-1 and DG = -6.67±0.05 kJ.mole-1. The effect of common anions and cations on the sorption has been examined. Sulphate, ascorbate and bromide ions enhances the sorption to some extent whereas nitrite, Pb(II), Fe(III), Al(III), Cu(II) and Co(II) decrease to sorption significantly. A possible mechanism has been envisaged for Zn(II)-SCN sorption onto PUF.

Removal of 2.4-dichloro phenoxyacetic acid from aqueous solution by adsorption on activated carbon. A kinetic study

The sorption of 2.4-dichloro phenoxyacetic acid (2.4-D) on two different activated carbons was determined using the batch equilibration technique. The calculated slopes of the Freundlich sorption isotherms were significantly less than 1. The (K) values were higher for the activated carbon which has the higher specific surface, and increased with NaCl concentration. The rate of attaining equilibrium of 2.4-D increased with a decrease in absorbent concentration. Dynamic modelling of the adsorption showed that a first order reversible kinetic model was followed for the adsorption process. The overall rate constant K′, the adsorption rate K1, the desorption rate constant K2, and the equilibrium constant Kc for the adsorption process were calculated.

Sorption of traces of silver ions onto polyurethane foam from acidic solution

The sorption of traces of silver ions onto polyurethane foam (PUF) has been investigated in detail. Maximum sorption of silver ( K d=6109 cm 3 g −1, %sorption>97.5%) has been achieved from 1 M nitric acid solution after equilibrating silver ions with ∼ 29 mg PUF for 20 min. The kinetics and thermodynamics of the sorption of silver ions onto PUF have also been studied. The sorption of silver ions onto PUF follows a first-order rate equation, which results as 0.177 min −1. The variation of sorption with temperature yields the values of Δ H=−56.1±3.2 kJ mol −1, Δ S=−159.7±10.5 J mol −1 K −1 and Δ G=−8.68±0.09 kJ mol −1 at 298 K with a correlation factor γ=0.9919. The sorption data were subjected to different sorption isotherms. The sorption follows Langmuir, Freundlich and Dubinin–Radushkevich (D–R) isotherms. The values of Langmuir isotherms Q=65.4±1.5 μmol g −1 and b=(4.79±1.16)×10 4 dm 3 mol −1 have been evaluated for Langmuir sorption constants, whereas the Freundlich sorption isotherm gives the value 1/ n=0.12±0.02 and A=0.15±0.03 mmol g −1. The D–R parameters computed were β=−0.000817±0.000206 mol 2 kJ −2, X m=76.8±8.7 μmol g −1 and E=24.7±3.2 kJ mol −1. The influence of common ions on the sorption was also examined. It is observed that Hg(II), thiourea, Al(III), thiocyanate and thiosulphate reduce the sorption, whereas Cu(II), citrate and acetate ions enhance the sorption significantly. It can be concluded that PUF may be used to remove traces of silver ions from its very dilute solutions or for its preconcentration from aqueous acidic solutions.

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.

Application of a mechanistic desorption-biodegradation model to describe the behavior of polycyclic aromatic hydrocarbons in peat soil aggregates

A procedure was developed to obtain three size fractions (2360< d p<1000, 1000< d p<710, and 710< d p<425 μm) of stable aggregates from Koopveen peat soil by application of an intense mixing regime prior to sieving of the soil material. The organic matter content, aggregation structure and the microstructure of these aggregates were determined and the particles were artificially contaminated with naphthalene and phenanthrene via a solvent phase. A nonlinear Freundlich sorption isotherm was determined for the naphthalene contaminated soil aggregates ( n=0.39; K F =1.13×10 −2 m 1.17 kg −0.39) . The applicability of a mathematical model, that describes sorption equilibrium, intra-particle mass-transfer, and nonlinear bacterial degradation kinetics, was tested by fitting results of dynamic desorption and biodegradation experiments, generated in this study and earlier work on the peat soil aggregates. The experimental data were described adequately although strong variations in the values of the fit parameter, the intra-particle porosity (0.30< ε<0.88), were found. This indicates the necessity of further investigations.

Sorption of L -methionine-sulphoximine on humic acids and clay minerals

The sorption of L-methionine-sulphoximine (MSX) on soil-extracted humic fractions (MW>20,000 Da), and mined clays (kaolinite and montmorillonite) was studied by a reversed-phase high-performance liquid chromatography method. The molecule, acting as an inhibitor of glutamine synthetase activity, was recently used in soil incubation assays for the determination of gross rates of N mineralization. Equilibrium data of MSX adsorbed on humic fractions and clay minerals were described by both the Freundlich and Langmuir sorption isotherms. It was observed that humic fractions were more effective than mined clay minerals in removing MSX from water. Most isotherms were of Langmuir type, indicating a higher affinity of MSX for sorbing sites which become increasingly saturated at higher equilibrium concentrations. Analysis of Langmuir empirical constants revealed that different adsorbing mechanisms took place. Results showed that when MSX is applied in soil incubation assays, sorption of MSX on soil colloids considerably reduces the availability of the inhibitor to target microorganisms, and renders the method unsuitable for the determination of the gross rate of N mineralization, especially when high levels of both organic matter and clay minerals are present in the soil.