[Show abstract][Hide abstract] ABSTRACT: The environmental behaviors of polycyclic aromatic hydrocarbons (PAHs) are mainly governed by their solubility and partitioning properties on soil media in a subsurface system. In surfactant-enhanced remediation (SER) systems, surfactant plays a critical role in remediation. In this study, sorptive behaviors and partitioning of naphthalene in soils in the presence of surfactants were investigated. Silica and kaolin with low organic carbon contents and a natural soil with relatively higher organic carbon content were used as model sorbents. A nonionic surfactant, Triton X-100, was used to enhance dissolution of naphthalene. Sorption kinetics of naphthalene onto silica, kaolin and natural soil were investigated and analyzed using several kinetic models. The two compartment first-order kinetic model (TCFOKM) was fitted better than the other models. From the results of TCFOKM, the fast sorption coefficient of naphthalene () was in the order of silica > kaolin > natural soil, whereas the slow sorbing fraction () was in the reverse order. Sorption isotherms of naphthalene were linear with organic carbon content () in soils, while those of Triton X-100 were nonlinear and correlated with CEC and BET surface area. Sorption of Triton X-100 was higher than that of naphthalene in all soils. The effectiveness of a SER system depends on the distribution coefficient () of naphthalene between mobile and immobile phases. In surfactant-sorbed soils, naphthalene was adsorbed onto the soil surface and also partitioned onto the sorbed surfactant. The partition coefficient () of naphthalene increased with surfactant concentration. However, the decreased as the surfactant concentration increased above CMC in all soils. This indicates that naphthalene was partitioned competitively onto both sorbed surfactants (immobile phase) and micelles (mobile phase). For the mineral soils such as silica and kaolin, naphthalene removal by mobile phase would be better than that by immobile phase because the distribution of naphthalene onto the micelles () increased with the nonionic surfactant concentration (Triton X-100). For the natural soil with relatively higher organic carbon content, however, the naphthalene removal by immobile phase would be better than that by mobile phase, because a high amount of Triton X-100 could be sorbed onto the natural soil and the sorbed surfactant also could sorb the relatively higher amount of naphthalene.
Journal of Environmental Science International. 01/2010; 19(5).
[Show abstract][Hide abstract] ABSTRACT: The applicability of in situ biobarrier or microbial filter technology for the remediation of groundwater contaminated with chlorinated solvent was investigated through column study. In this study, the effect of packing materials on the reductive dechlorination of PCE was investigated using Canadian peat, Pahokee peat, peat moss and vermicompost (or worm casting) as a biobarrier medium. Optimal conditions previously determined from a batch microcosm study was applied in this column study. Lactate/benzoate was amended as electron donors to stimulate reductive dechlorination of PCE. Hydraulic conductivity was approximately and no difference was found among the packing materials. The transport and dispersion coefficients determined from the curve-fitting of the breakthrough curves of using CXTFIT 2.1 showed no difference between single-region and two-region models. The reductive dechlorination of PCE was efficiently occurred in all columns. Among the columns, especially the column packed with vermicompost exhibited the highest reductive dechlorination efficiency. The results of this study showed the promising potential of in situ biobarrier technology using peat and vermicompost for the remediation of groundwater contaminated with chlorinated solvents.
Journal of Environmental Science International. 01/2007; 16(10).
[Show abstract][Hide abstract] ABSTRACT: A new three-parameter empirical isotherm model (the Song isotherm model, hereinafter) is proposed. This model satisfies the Henry's law and the Freundlich isotherm model in the low and high concentration ranges, respectively. We applied this model to the single-solute sorption of 2-chloro-, 3-cyano-, and 4-nitrophenol from water to montmorillonites organically modified with either hexadecyltrimethylammonium (HDTMA) cation or both HDTMA and tetramethylammonium (TMA) dual cations. Sorption to organoclays (i.e., organically modified clays) modified with the long-hydrocarbon chain organic cations or the short- and long-hydrocarbon chain dual organic cations usually occurs by a partition mechanism. Sorption of polar organic compounds to organoclays, however, becomes nonlinear when the solution-phase concentration covered is more than 3 orders of magnitude. The three parameters contained in the presently proposed model could be estimated from the plot, log(q/c) versus log c. The partition coefficient in the Henry's law region (K) can be estimated from the ordinate value of the asymptote in the low concentration region, the Freundlich index (n) can be estimated from the slope of the asymptote in the high concentration region, and the parameter (beta) corresponding to the crossover point can be estimated from the intersection point of the two asymptotes. By performing nonlinear curve fitting to the raw data, q versus c, using the initial guesses estimated from the manipulated data, log-(q/c) versus log c, the optimum set of parameters could be determined without worrying much over the annoying local minima. The Song model was compared with other existing two- and three-parameter isotherm models. The Song model fitted our experimental data better than the Langmuir and Freundlich models and showed nearly the same goodness-of-fit as the Redlich-Peterson and dual-mode models. The obvious merit of the Song model is that it provides us with the partition coefficient in the Henry's law region. The organic carbon-normalized partition coefficients in the Henry's law region were found to be about 1 order of magnitude higher than the corresponding octanol-water partition coefficients, at least for the phenolic compounds covered in this study.
Environmental Science and Technology 03/2005; 39(4):1138-43. · 5.26 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Single- and bi-solute sorption and desorption of 2,4-dichlorophenol (2,4-DCP) and 2,4,5-trichlorophenol (2,4,5-TCP) in montmorillonite modified with hexadecyltrimethylammonium (HDTMA) were investigated using multi-step sorption and desorption procedure. Effect of pH on the multi-step sorption and desorption was investigated. As expected by the magnitude of octanol-water partition coefficient, Kow, both sorption and desorption affinity of 2,4,5-TCP was higher than that of 2,4-DCP at pH 4.85 and 9.15. For both chlorophenols, the protonated speciation (at pH 4.85) exhibited a higher affinity in both sorption and desorption than the predominant deprotonated speciation (about 95% and 99% of 2,4-dichlorophenolate and 2,4,5-trichlophenolate anions at pH 9.15, respectively). Desorption of chlorinated phenols was strongly dependent on the current pH regardless of their speciation in the previous sorption stage. Freundlich model was used to analyze the single-solute sorption and desorption data. No appreciable desorption-resistant (or non-desorbing) fraction was observed in organoclays after several multi-step desorptions. This indicates that sorption of phenols in organoclay mainly occurs via partitioning into the core of the pseudo-organic medium, thereby causing desorption nearly reversible. In bisolute competitive systems, sorption (or desorption) affinity of both chlorophenols was reduced compared to that in its single-solute system due to the competition between the solutes. The ideal adsorbed solution theory (IAST) coupled to the single-solute Freundlich model successfully predicted bisolute multi-step competitive sorption and desorption equilibria.
Water Air and Soil Pollution 01/2005; 166(1):367-380. · 1.75 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A simple mathematical model was proposed to analyze the enhancement of Cr(VI) reduction when sand materials are added to the
zero valent iron (ZVI). Natural decay of Cr(VI) in a control experiment was analyzed by using a zero-order decay reaction.
Adsorption kinetics of Cr(VI) to sand was modeled as a first-order reversible process, and the reduction rate by ZVI was treated
as a first-order reaction. Natural decay of Cr(VI) was also included in other experiments, i.e., the adsorption to sand, the
reduction by ZVI, and both adsorption and reduction when sand and ZVI are present together. The model parameters were estimated
by fitting the solution of each model to the corresponding experimental data. To observe the effect of sand addition to ZVI,
both adsorption and reduction rate models were considered simultaneously including the natural decay. The solution of the
combined model was fitted to the experimental data to determine the first-order adsorption and reduction rate constants when
sand as well as ZVI is present. The first-order reduction rate constant in the presence of sand was about 35 times higher
than that with ZVI only.
Korean Journal of Chemical Engineering 01/2005; 22(1):67-69. · 1.06 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Four diffusion models for the dynamic adsorber, i.e. LDF model, single diffusivity diffusion model, two diffusivity diffusion
model for beds packed with bidisperse and/or zeolite-type particles, were considered. The third moments for the four diffusion
models were obtained. Relations between the system parameters involved in each model were derived by matching mean, vanance
or the third moment between diffusion models. The two relations from either variance or the third moment matching were examined
to investigate which one is superior when model simplification is required, by comparing the time domain elution curves for
the single and the two diffusivity diffusion models. For the symmetric elution curves, relation from the variance matching
is much better as expected, than the relation matching the third moment which measures skewness about mean. As the elution
curves become highly asymmetric, eluting shortly after injection and exhibiting long tailing due to both the small intraparticle
diffusivities and small space time in the adsorber, either relation failed to satisfactorily simplify the two diffusivity
diffusion model. Contrary to the expectation that the third moment matching would work better in the asymmetric curves due
to the nature of the third moment, variance matching still gives slightly better results. Relation from the variance, instead
of the third moment, matching is strongly recommended for model simplification due to its simplicity in formula.
Korean Journal of Chemical Engineering 01/1996; 13(1):60-66. · 1.06 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Single- and bisolute competitive sorption of phenols (2-chlorophenol, 3-cyanophenol and 4-nitrophenol) onto montmorillonite
modified with cationic surfactant (hexadecyltrimethylammonium, HDTMA cation) was investigated. In single-solute sorption,
sorption affinity increased in the order of 2-chlorophenol>4-nitrophenol>3-cyanophenol, as expected from the magnitude of
the octanol-water partition coefficient (K
ow). The difference in affinity is mainly attributed to the hydrogen bonding with the water molecules incorporated in the sorbed
phase. The sorption affinity of the phenolic compounds onto the HDTMA-montmorillonite was in the order of pH 7>pH 3≫pH 11.5.
Compared to uptake at pH 3 and 7, the uptake at pH 11.5 was quite low. The reduced uptake at pH 11.5 is attributed to lower
solubility of anions in the core of the organic medium due to the unfavorable hydrophobic interaction between hydrated anions
and nonpolar organic medium and thus anions adsorbing near the surface of the nonpolar organic medium. Solubility-normalized
Freundlich model fitted the single-solute sorption data well. Competition between the solutes in bisolute sorption reduced
the sorbed amount of each solute compared with that in the single-solute system. The ideal adsorbed solution theory (IAST)
coupled with the solubility-normalized Freundlich model predicted the bisolute competitive sorption data successfully. The
solubility-normalized model was analyzed to characterize sorption mechanism of phenols onto HDTMA-montmorillonite at very
low (Henry's law resion) and at high concentration (Ralout's law region).
[Show abstract][Hide abstract] ABSTRACT: Single- and bi-solute sorption and desorption of 2-chlorophenol (2-CP) and 2,4,5-trichlorophenol (2,4,5-TCP) in montmorillonite
modified with hexadecyltrimethyl-ammonium (HDTMA) were investigated by sequential sorption and desorption. Effect of pH on
the sequential sorption and desorption was investigated. As expected by the magnitude of octanol: water partition coefficient
(Kow), both sorption and desorption affinity of 2,4,5-TCP was higher than that of 2-CP at pH 4.85 and 9.15. For both chlorophenols,
the protonated speciation (at pH 4.85) exhibited a higher affinity in both sorption and desorption than the predominant deprotonated
speciation (about 80% and 99% of 2-chlorophenolate and 2,4,5-trichlophenolate anions at pH 9.15, respectively). Desorption
of chlorinated phenols was strongly dependent on the current pH regardless of their speciation in the previous sorption stage.
Freundlich model was used to analyze the single-solute sorption and desorption data. No appreciable desorption-resistant (or
non-desorbing) fraction was observed in organoclays after several sequential desorptions. This indicates that sorption of
phenols in organoclay mainly occurs via partitioning into the core of the pseudo-organic medium, thereby causing desorption
nearly reversible. In bisolute competitive systems, sorption (or desorption) affinity of both chlorophenols was reduced compared
to that in its single-solute system due to the competition between the solutes. The ideal adsorbed solution theory (IAST)
coupled with the single-solute Freundlich model was positively correlated with the bisolute sequential competitive sorption
and desorption equilibria.
Korean Journal of Chemical Engineering 23(1):63-70. · 1.06 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Sorption and desorption kinetics of chlorophenols, 2-chlorophenol (2-ChP), 2,4-dichlorophenol (2,4-DChP) and 2,4,5-trichlorophenol
(2,4,5-TChP), in montmorillonite modified with hexadecyltrimethyl ammonium cations (HDTMA-mont) were investigated by using
laboratory batch adsorbers. To investigate the effect of chemical concentration and sorbent weight on the sorption or desorption
rate constants, the initial chemical concentration and sorbent weight were varied from 50 to 150 mg/L and from 0.2 to 1.0
g, respectively. A one-site mass transfer model (OSMTM) and two compartment first-order kinetic model (TCFOKM) were used to
analyze kinetics. The OSMTM applicable to desorption rate analysis was newly derived. As expected from the number of model
parameters involved, the three-parameter TCFOKM was better than the two-parameter OSMTM in describing sorption and desorption
kinetics of chlorophenols in HDTMA-mont. The mass transfer coefficient for sorption (ks) in OSMTM generally increased as K
value increases, except for 2,4,5-TChP, while the mass transfer coefficient for desorption (k
) consistently increases as K
value decreases, due to the weaker hydrophobic interaction between the solute and the organoclay. Since most sorption and
desorption complete in an hour and half an hour, respectively, k
values were found to be greater than k
values for all three solutes studied. The fraction of the fast sorption (or desorption) and the first-order sorption (or
desorption) rate constants for the fast and slow compartments in TCFOKM were determined by fitting experimental data to the
TCFOKM. The results of kinetics reveal that the fraction of the fast sorption or desorption and the sorption rate constants
in the fast and slow compartments were in the order 2,4,5-TChP>2,4-DChP>2-ChP, which agrees with the magnitude of the octanol-water
partition coefficient, K
. The first-order sorption rate constants in the fast and slow compartments were found to vary 101–102 hr−1 and 10−3–10−2 hr−1, respectively. However, the desorption rate constants in the fast and slow compartments were not correlated well withK
. The first-order desorption rate constants in the fast compartment (101−102 hr−1) were found to be much larger than those in the slow compartment (10−3–10−4 hr−1). Sorption affinity and desorption resistance of each chlorophenol in 50% HDTMA-mont were found to show the same tendency:
the weakly-sorbed chlorophenol (i.e., 2-ChP) was easily desorbed, while the strongly-sorbed chlorophenol (i.e., 2,4,5-TChP)
was rather resistant to desorption.
Korean Journal of Chemical Engineering 22(6):857-864. · 1.06 Impact Factor