Large Kd Research Articles

Determining distribution coefficients for low cost adsorbents

AbstractAs with other construction materials, coal fly ash contains trace metals that can leach into the natural environment. As part of a broader effort to encourage appropriate coal combustion product use in infrastructure applications (e.g., road construction, stabilization, and structural fill), this study evaluated traditional and low‐cost adsorbent alternatives for their capacity to attenuate trace metals. Batch sorption tests were used as a preliminary screen for a wide variety of low cost (e.g., steel byproducts, rubber dust, and compost) and innovative materials (e.g., kudzu, biofilm, and pond weed) as well as conventional materials (activated carbon, alumina, and zeolites). The removal rates were demonstrated in this study by observing the calculated distribution coefficient (Kd) which were determined using a program called MATLAB. Limestone and steel byproducts were found to be particularly effective with large Kd values of 15,740, 1,520, and 540 L kg−1 for cadmium, chromium, and selenium and, for ladle refractory and mill scale, Kd values of 3,910, 670, and 1,760 L kg−1 were observed. Among the three metals tested for this study, it was observed that most low cost and innovative materials removed cadmium quite efficiently; however, the removal of selenium and chromium depended on the substrate and prevailing pH. In general, these results suggest that alternative materials may have relevance in niche applications where leaching is a concern that can be addressed through enhanced attenuation capacity via blending or layering of adsorbents.

Effect of crystals’ surface shape distortion on conversion efficiency of third harmonic generation

In the field of inertial confinement fusion (ICF), UV laser can effectively improve the beam-target coupling efficiency and suppress the hydrodynamic instability of laser plasma interaction. Using large aperture KDP crystal or KD*P crystal to triple the frequency of laser created by high power solid-state laser facility (wavelength is 1 μm) is an effective way to obtain high power UV laser output. At present, most high power laser facilities take method of I/II type third harmonic generation. The phase matching condition is required in the third harmonic generation, and the conversion efficiency is easily influenced by the detuned angle of crystals. The quality of the return light spot of crystals’ surface can reflect the state of wavefront distortion, and then evaluate the degree of angle-detuning at the crystal. The factors which create detuned angle are analyzed and judged, within which the surface shape distortion of crystals (PV is more than 30 μm) caused by clamping and gravity is the main part. According to improving the surface shape of crystals (PV is less than 10 μm) in the experiment, the quality of the return light spot of crystals has been significantly improved, and then the conversion efficiency of third harmonic generation has an obvious increase.

Dynamic depth distribution of cesium-133 near soil surfaces in packed soils under multiple simulated rains

Various 137Cs conversion models have been used to predict soil erosion. A knowledge of the initial distribution of 137Cs is vital to improve soil loss prediction. The objectives were to (1) characterize the dynamic distributions of 133Cs near the soil surfaces in multiple rains spiked with 133Cs using a rainfall simulator, and (2) further estimate the relaxation mass depth (H) for use in an improved 137Cs mass balance model. Three silt loam soils were packed to soil boxes (1 × 0.5 × 0.1 m) and rained on at 30 mm h−1 and 10% slope in five consecutive rains. Soil cores (62.5 mm i.d.) were taken following each rain and were sectioned in the 1–10-mm intervals. Event runoff and sediment were collected. Cs+ was extracted with an NH4OAc method using a centrifuge procedure and analyzed with Inductively Coupled Plasma-Mass Spectrometer. The results showed initial Cs distributions near the soil surfaces were approximately exponential, and the mean H value could adequately characterize the initial Cs distributions for each soil for any sequence of rains. The averaged H values were 0.338, 0.304, and 0.354 g cm−2 for the three soils, equivalent to the soil depths of 2.76, 2.20, and 2.58 mm, indicating that majority of Cs was distributed within the top 3-mm depth. Cs+ was strongly adsorbed by the soils as indicated by the large Kd values of >32.6 L kg−1, showing the limited mobility of the freshly deposited Cs+ in the soils. Better H estimation should lead to more accurate soil loss prediction using the improved Cs mass balance model.

Facile preparation of Fe3O4/MoS4 for ultra fast and highly selective uptake towards Hg2+, Pb2+ and Ag+

We demonstrate the newly prepared magnetite/molybdenum sulfide (Fe3O4/MoS4) composite reacted from protonated Fe3O4 and MoS42– and its highly selective and ultra rapid uptake for Ag+, Pb2+ and Hg2+. The Fe3O4/MoS4 can separate Hg2+, Ag+ and Pb2+ from complex metal mixtures with high selectivity (order is Hg2+>Ag+>Pb2+>>Co2+/Ni2+/Cu2+/Zn2+/Cd2+), which is extremely difficult to do with other materials. The maximum adsorption capacities (qm) for Ag+ and Pb2+ reach up to 546.6 and 101.6 mg/g, respectively, determining an obvious advantage over most known sorbents. Fast sorption kinetics of Pb2+, Hg2+ and Ag+ is found, achieving nearly complete uptake (>99.99%) and very large Kd (106–107 mL/g) within 1–5 min. Sharply reduced concentrations (<1 ppb) of Ag+, Pb2+ and Hg2+ are obtained after sorption in several minutes, meeting safe limit of drinking water. Furthermore, Fe3O4/MoS4 is capable of trapping Ag+/Pb2+ efficiently (>99.9%) over a wide pH range (2.5–7.0 for Ag+, 4.5–6.0 for Pb2+). High loading of MoS42- upon Fe3O4 (MoS4:Fe3O4 molar ratio is 1:2) and strong affinity between material interfaces and metal ions endow the appealing trapping capability and ultrahigh selectivity. Thanks to the ultra fast and outstanding selectivity, the Fe3O4/MoS4 is expected to be one of top materials for removing heavy metals in wastewater.

MoS2/Au0/N-CNT derived from Au(III) extraction by polypyrrole/MoS4 as an electrocatalyst for hydrogen evolution reaction

The nanotube type MoS42−/polypyrrole (MoS4-Ppy) is newly synthesized which exhibits exceptional uptake capability for Au(III) with a high removal rate of >99.99% and large Kd of >107 mL/g. Through simple calcination, the Au-loaded MoS4-Ppy is successfully converted to nitrogen-doped carbon nanotubes (N-CNT) decorated with MoS2 nanosheets as well as Au0 nanoparticles, forming a novel composite of MoS2/Au0/N-CNT. The conductivity of MoS2/Au/N-CNT is substantially improved by the highly conductive N-CNT and Au0 metal. In addition, the N-CNT can effectively eliminate the aggregation of MoS2 sheets and Au0 particles, thus endowing more exposed active sites. The optimized MoS2/Au0/N-CNT displays good electrocatalytic performance towards hydrogen evolution reaction (HER). For the first time, we demonstrate the MoS4-Ppy is a promising material for efficient extraction and recovery of trace amounts of precious metal Au from gold-bearing leachates, and the subsequent product MoS2/Au/N-CNT can act as an effective HER electrocatalyst. The fabrication process of the composite material can not only remediate water contamination but also reuse precious metals. This dual-use approach opens a new way to explore effective sorbents for recovery of trace of gold and apply them in catalysis and sensing fields.

Separation of 90Sr from nuclear waste by crystalline complex phosphates of Ce(IV) and Zr(IV)

Large amounts of radioactive Sr produced in nuclear reactor need to be separated for alternate use or safe disposal. Herein effective separation of radioactive Sr2+ by crystalline complex phosphates, namely a tunnel structured K2Ce(PO4)2 (KCP) and a layer structured K2Zr(PO4)2 (KZP) is reported. These phosphates were prepared by high temperature solid state reaction method and characterized by X-ray diffraction using synchrotron X-ray sources. Ion exchange properties of these materials have been evaluated by using solutions of radioactive 85Sr. Both the materials show quantitative separation of Sr2+ but at different pH. Distribution constants (Kd) show increasing trend with increasing pH and show maximum values ∼ 8000 at pH 14 for KCP and ∼ 30,000 in neutral medium for KZP. The ion exchange capacities (qe) increase with increasing Sr2+ ions concentration and the typical values of qe are ∼ 521 μmol/g for KCP and ∼ 603 μmol/g for KZP. Correlation of structure and ion exchange properties indicated that the layered structure of KZP is the origin for its large Kd. The studies on kinetics and exchange isotherms of both KCP and KZP suggest for pseudo-second order favorable chemisorptions processes. From ex situ high temperature reactions, it is proposed that these lattices can be converted to stable apatite or NZP type matrices with the separated Sr2+ ions from the nuclear waste.

Diffusion of radiosulphate and radiocaesium in kaolinite clay (KGa-2): Testing the applicability of the pore water diffusion model

The effective diffusion coefficients (De) and rock capacity factors (α) for radiosulphate and radiocaesium in compacted kaolinite (KGa-2) were measured as a function of the concentration of NaClO4 in the contacting solution to test the effect of salinity on diffusion of these species. Solid-liquid distribution coefficients (Kd) were derived from α and compared with Kd values from batch sorption experiments using dispersed clay suspensions. De values for radiosulphate (3.3–8.0 × 10−11 m2 s−1) showed no substantial dependence on the concentration of NaClO4. The diffusion Kd values (9–40 L kg−1) indicated a weak sorption process, confirmed by the low Kd values measured in the batch sorption experiments. No unambiguous conclusion could be drawn regarding a potential salinity effect on radiocaesium De values (1.4–3.0 × 10−10 m2 s−1). The diffusion-derived Kd of 134Cs (53–498 L kg−1) varied inversely with the NaClO4 concentration, consistent with a cation exchange process, and substantially decreased in the presence of stable Cs, suggesting the presence of specific sites for 134Cs that become saturated at high Cs concentrations. Structural analyses indicated an illite content of around 1.7%, which explained the generally large Kd values for radiocaesium. Finally, the correlation between measured De values and the respective diffusion coefficients in bulk water (Dw) was examined for a number of species, including radiosulphate and radiocaesium in the presence of stable Cs, along with additional data gathered from other species. Both variables were highly correlated, confirming the validity of the pore water diffusion model, but only in the absence of specific interaction with the clay.

Ligand exchange adsorption and coordination structure of Pd on δ-MnO2 in NaCl solution

Palladium is highly accumulated in ferromanganese (Fe-Mn) nodules and crusts relative to its concentration in seawater but the mechanism by which Pd(II) is incorporated remains poorly understood, probably because the Pd concentration in Fe-Mn nodules and crusts is fairly low. In this study, we investigated the local coordination structure of Pd(II) adsorbed on δ-MnO2, using X-ray absorption fine structure spectroscopy to clarify the mechanism by which Pd is incorporated into Fe-Mn nodules and crusts. Adsorption experiments of Pd(II) on δ-MnO2 were conducted in 0.1 and 0.5M NaCl solutions, in which the negatively charged chloride complexes PdCl42−, PdCl3−, and PdCl3OH2− were predominant species. The distribution coefficient of Pd between δ-MnO2 and solution, Kd(Pd)=[Pd]solid/[Pd]solution (L/kg), increased from ~2×103 to ~4×106 with increasing pH. X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) analyses indicated that Pd was adsorbed on δ-MnO2 through ligand exchange, from Cl coordination to O coordination. Furthermore, curve fitting of EXAFS spectra demonstrated the formation of two different inner-sphere complexes, bidentate-mononuclear and bidentate-binuclear complexes, and this finding was supported by density functional theory calculations. The formation of inner-sphere complexes is reasonable given the relatively large Kd(Pd) values obtained from adsorption experiments and the large apparent Kd(Pd) values calculated from reported data on Fe-Mn nodules and crusts and seawater.

Ligand-Protein Affinity Studies Using Long-Lived States of Fluorine-19 Nuclei.

The lifetimes TLLS of long-lived states or TLLC of long-lived coherences can be used for the accurate determination of dissociation constants of weak protein-ligand complexes. The remarkable contrast between signals derived from LLS or LLC in free and bound ligands can be exploited to search for weak binders with large dissociation constants KD > 1 mM that are important for fragment-based drug discovery but may escape detection by other screening techniques. Alternatively, the high sensitivity of the proposed method can be exploited to work with large ligand-to-protein ratios, with an evident advantage of reduced consumption of precious proteins. The detection of (19)F-(19)F long-lived states in suitably designed fluorinated spy molecules allows one to perform competition binding experiments with high sensitivity while avoiding signal overlap that tends to hamper the interpretation of proton spectra of mixtures.

Dispersion and kinematics of multi-layer non-hydrostatic models

Multi-layer non-hydrostatic models are gaining popularity in studies of coastal wave processes owing to the resolution of the flow kinematics, but the linear dispersion relation remains the primary criterion for assessment of model convergence. In this paper, we reformulate the linear governing equations of an N-layer model into Boussinesq form by writing the non-hydrostatic terms as high-order derivatives of the horizontal flow velocity. The equation structure allows implementation of Fourier analysis to provide a [2N−2, 2N] expansion of the velocity at each layer. A variable transformation converts the governing equations into separate flux- and dispersion-dominated systems, which explicitly give an equivalent Pade´ expansion of the wave celerity for examination of the convergence and asymptotic properties. Flow continuity equates the depth-integrated horizontal velocity to the celerity and verifies the analytical solution. The surface-layer velocity, which is driven by the kinematic free surface boundary condition, shows a positive error and converges monotonically to the solution of Airy wave theory. When the depth parameter kd > 2N, flow reversal occurs in the sub-surface layers to offset overestimation of the surface velocity and to better approximate the flux. This model internal mechanism facilitates convergence of the celerity at large kd and benefits applications on wave transformation. Such non-physical flow reversal, however, might complicate studies that require detailed wave kinematics.

Sorption affinities of sulfamethoxazole and carbamazepine to two sorbents under co-sorption systems

The Kd of sulfamethoxazole (SMX) on activated carbon (AC) was larger than that of SMX on single-walled carbon nanotubes (SC), but the competition of SMX with carbamazepine (CBZ) for adsorption sites was weaker on AC than SC. Thus, a large Kd value does not necessarily reflect a high affinity. The analysis of the apparent sorption, competition, desorption hysteresis, and the sorption thermodynamics for SMX and CBZ did not provide sufficient information to distinguish their sorption affinities. The release of the adsorbed CBZ was not altered with SMX as the competitor, but SMX release increased significantly after CBZ addition. The higher sorption affinity of CBZ may be explained by the interactions of the CBZ benzene rings with the aromatic structures of the adsorbents. Although the thermodynamic meaning cannot be described, the release ratio of the adsorbed pollutants provides useful information for understanding pollutant sorption strength and associated risks.

Size distribution studies of 137Cs in river water in the Abukuma Riverine system following the Fukushima Dai-ichi Nuclear Power Plant accident

The occurrence of 137Cs in size fractionated samples in river water from the Abukuma River system, (the Kuchibuto and Abukuma Rivers, five sampling events for three sites) was studied from June 2011 – approximately some three months after the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident until December 2012. The total concentration of 137Cs (mBq/L) in river water was generally high at the upper stream site in the Yamakiya District within the evacuation/off-limits zone. The 137Cs concentration was about 1Bq/L for the first sampling campaign (June 2011) at all sites, but then decreased substantially to about one-tenth of that by the time of a second sampling campaign (November or December 2011). The 137Cs in the <0.45μm fraction was present exclusively as a dissolved species rather than as a species adsorbed on suspended solids or complexed with organic materials. The contribution of the dissolved fraction ranged from 1.2 to 48.9% (averaged 20%) of the total concentration of 137Cs throughout the observation period. The maximum contribution of 137Cs was found in the silt size fraction (3–63μm), which can be explained by the relatively large Kd values and the suspended solids (SS) concentration of this size fraction. Although the concentration (Bq/g) of 137Cs ineach size fraction did not show any significant trends and/or variations for any of the sampling campaign, Kd values for each site increased with time. Furthermore, it was found that the Kd values decreased with distance from the headstream in the off-limits zone. Thus, the data acquired in this study give an overview of the radiological situation for Fukushima including temporal and spatial variation of radiocaesium in a natural riverine system, within a few years after the accident.

Prediction of colloidal stability of high concentration protein formulations

A major aspect determining the colloidal properties of proteins in solution is the interaction between them and with surrounding molecules. These interactions can be described by the concentration dependency of the protein diffusivity (kD), as derived by dynamic light scattering and was determined for different solutions of monoclonal antibodies varying in pH, ionic strength and presence/absence of co-solute(s). Concerning colloidal stability, protein solutions of different kD values are evaluated, based on their initial solution opalescence, to assess protein association. The current investigation shows that solution conditions with large kD values, indicating high repulsive protein–protein interactions, show lower initial opalescence, compared to solution conditions with low kD values. Upon applying stirring stress, to assess colloidal stability, the trend is such that, the higher kD values are, the more stable the protein solutions are, as long as the thermodynamic and conformational stability is not impaired. Besides, kD allows ranking of solution conditions for highly concentrated immunoglobulin solutions up to concentrations of ∼200 mg mL−1 with regard to protein self-association and thus opalescent properties. The present study shows that the protein interaction parameter kD can be used as a surrogate parameter for a qualitative prediction of protein association and, thus, colloidal protein stability.

Chromatographic Separation of Nuclear Rare Metals by Highly Functional Xerogels

The uptake behavior of Cs, Pd, Mo, Re and Tc on highly functional xerogels (microcapsules: MCs), the characterization of MCs and the chromatographic separation for the simulated HLLW (28 components) and the spent fuel solution were examined by batch and column methods. Granular MCs of ammonium tungstophosphate (AWP) encapsulated with calcium alginate (CaALG) matrices exhibited a high selectivity towards Cs+, and a relatively large separation factor (α) of Cs+/Rb+ above 10 was obtained. The mutual separation of Cs+/Rb+ was thus accomplished through the packed column. The novel MCs of insoluble ferrocyanides (CuFC) prepared by direct method had an excellent selectivity towards Pd2+; relatively large Kd values above 105 cm3/g were obtained. The chromatographic separation of Pd2+/Rh3+/RuNO3+ in simulated HLLW was accomplished using thiourea-HNO3 eluent. The extractants (LIX63, MIDOA and TOA) can be encapsulated with the alginate polymer gels. The MCs enclosing the above extractants exhibited high selectivity towards Mo(VI), Re(VII) and Tc(VII) ions, and the chromatographic separation for simulated HLLW and spent fuel solutions was accomplished by using stepwise elution methods. The precise separation system combined the above processes is effective for the recovery of nuclear rare metals from HLLWs.

Study on adsorption behavior of cesium using ammonium tungstophosphate (AWP)-calcium alginate microcapsules

A functional microcapsule was prepared by encapsulating the fine crystalline ammonium tungstophosphate (AWP) in calcium alginate polymer (CaALG). The characterization of AWP-CaALG microcapsule was examined by SEM and EPMA. The adsorption behavior of Cs(I), Rb(I), Sr(II), Pd(II), Ru(III), Rh(III), La(III), Ce(III), Dy(III) and Zr(IV) was investigated by the batch method. The batch experiments were carried out by varying the shaking times, HNO3 concentration, and initial concentration of metal ions. Relatively large Kd values above 105 cm3/g for Cs(I) were obtained in the range of 0.1–5 M HNO3, resulting in a separation factor of Cs/Rb exceeding 102. In contrast, the Kd values of Sr(II), Pd(II), Ru(III), La(III), Dy(III), Ce(III) and Zr(IV) were considerably lower than 50 cm3/g. The Kd value of Cs(I) decreased in the order of the coexisting ions, H+ > Na+ ≫ NH4+, and a linear relationship with a slop of about −1 was obtained between log Kd and log [NH4+] ([NH4+] > 0.01 M). The adsorption of Cs(I) was found to be controlled by chemisorption mechanism, and followed a Langmuir-type adsorption equation. A high uptake percentage of 99.4% for Cs(I) was obtained by using the dissolved solutions of spent fuel from FBR-JOYO (JAEA).

Selective uptake of plutonium (IV) on calcium alginate gel polymer and TBP microcapsule

The uptake behavior of Pu(IV) has been investigated by using calcium alginate gel polymer (CaALG) and TBP microcapsules (TBP-CaALG). The characterization of CaALG and TBP-CaALG was examined by SEM and IR, and the uptake properties and distribution of Pu(IV) ions were estimated by batch method. The uptake rate of Pu(IV) on CaALG and TBP-CaALG in the presence of 5 M HNO3 was attained within 6 and 4 h, respectively, and Kd values for CaALG and TBP-CaALG after 7 h-shaking were 50.2 and 53.2 cm3/g, respectively. Relatively large Kd values (90.3–425 cm3/g) were obtained for fresh CaALG and TBP-CaALG in the presence of 0.5–2 M HNO3. Thus CaALG and TBP-CaALG are effective for the separation of Pu(IV) in the presence of highly concentrated HNO3.

Degradation Kinetics of Carbohydrate Fractions of Ruminant Feeds Using Automated Gas Production Technique

The current ruminant feeding models require parameterization of the digestion kinetics of carbohydrate fractions in feed ingredients to estimate the supply of nutrients from a ration. Using an automated gas production technique, statistically welldefined digestion rate of carbohydrate, including soluble carbohydrate, can be estimated in a relatively easy way. In this study, the gas production during in vitro fermentation was measured and recorded by an automated gas production system to investigate degradation kinetics of carbohydrate fractions of a wide range of ruminant feeds: corn silage, rice straw, corn, soybean hull, soybean meal, and cell mass from lysine production (CMLP). The gas production from un-fractionated, ethanol insoluble residue and neutral detergent insoluble residue of the feed samples were obtained. The gas profiles of carbohydrate fractions on the basis of the carbohydrate scheme of the Cornell Net Carbohydrate and Protein System (A, B1, B2, B3 and C) were generated using a subtraction approach. After the gas profiles were plotted with time, a curve was fitted with a single-pool exponential equation with a discrete lag to obtain kinetic parameters that can be used as inputs for modern nutritional models. The fractional degradation rate constants (Kd) of corn silage were 11.6, 25.7, 14.8 and 0.8%/h for un-fractioned, A, B1 and B2 fractions, respectively. The values were statistically well estimated, assessed by high t-value (>12.9). The Kd of carbohydrate fractions in rice straw were 4.8, 21.1, 5.7 and 0.5%/h for un-fractioned, A, B1 and B2 fractions, respectively. Although the Kd of B2 fraction was poorly defined with a t-value of 4.4, the Kd of the other fractions showed tvalues higher than 21.9. The un-fractioned corn showed the highest Kd (18.2%/h) among the feeds tested, and the Kd of A plus B1 fraction was 18.7%/h. Soybean hull had a Kd of 6.0, 29.0, 3.8 and 13.8%/h for un-fractioned, A, B1 and B2, respectively. The large Kd of fraction B2 indicated that NDF in soybean hull was easily degradable. The t-values were higher than 20 except for the B1 fraction (5.7). The estimated Kd of soybean meal was 9.6, 24.3, 5.0%/h for un-fractioned, A and B1 fractions, respectively. A small amount of gas (5.6 ml at 48 ho of incubation) was produced from fermentation of CMLP which contained little carbohydrate. In summary, the automated gas production system was satisfactory for the estimation of well defined (t-value >12) kinetic parameters and Kd of soluble carbohydrate fractions of various feedstuffs that supply mainly carbohydrate. The subtraction approach, however, should be applied with caution for some concentrates, especially those which contain a high level of crude protein since nitrogen-containing compounds can interfere with gas production.

Fast multipole accelerated boundary element method (FMBEM) for solution of 3D scattering problems

Wideband FMBEM codes are challenging to implement since there are problems at both very low and high frequencies. Substantially different schemes for function representation and translation are efficient for low and high frequency ranges. We present a method which is suitable for solution both high and low frequency problems since it implements a switch between different representations and uses fast translation methods appropriate to each representation. For a high frequency problem the switch between representations may occur at some intermediate levels of hierarchical space subdivision of the FMM. We also present an FMM-based preconditioner used in the flexible GMRES iterative solver for scattering problems and discuss example problems computed in range 0.001&amp;lt;kD&amp;lt;200, where k is the wave number and D is the size of the computational domain. The theoretical and experimental computational complexity of our algorithm is approximately O((kD)3) at large kD with relatively small asymptotic constant and the algorithm allows to solve problems with up to million nodes used for surface discretization in the range tested on a conventional personal computer.

Biodegradation of PAHs and PCBs in Soils and Sludges

Results from a multi-year, pilot-scale land treatment project for PAHs and PCBs biodegradation were evaluated. A mathematical model, capable of describing sorption, sequestration, and biodegradation in soil/water systems, is applied to interpret the efficacy of a sequential active–passive biotreatment process of organic chemicals on remediation sites. To account for the recalcitrance of PAHs and PCBs in soils and sludges during long-term biotreatment, this model comprises a kinetic equation for organic chemical intraparticle sequestration process. Model responses were verified by comparison to measurements of biodegradation of PAHs and PCBs in land treatment units; a favorable match was found between them. Model simulations were performed to predict on-going biodegradation behavior of PAHs and PCBs in land treatment units. Simulation results indicate that complete biostabilization will be achieved when the concentration of reversibly sorbed chemical (SRA) reduces to undetectable levels, with a certain amount of irreversibly sequestrated residual chemical (SIA) remaining within the soil particle solid phase. The residual fraction (SIA) tends to lose its original chemical and biological activity, and hence, is much less available, toxic, and mobile than the “free” compounds. Therefore, little or no PAHs and PCBs will leach from the treatment site and constitutes no threat to human health or the environment. Biotreatment of PAHs and PCBs can be terminated accordingly. Results from the pilot-scale testing data and model calculations also suggest that a significant fraction (10–30%) of high-molecular-weight PAHs and PCBs could be sequestrated and become unavailable for biodegradation. Bioavailability (large Kd, i.e., slow desorption rate) is the key factor limiting the PAHs degradation. However, both bioavailability and bioactivity (K in Monod kinetics, i.e., number of microbes, nutrients, and electron acceptor, etc.) regulate PCBs biodegradation. The sequential active–passive biotreatment can be a cost-effective approach for remediation of highly hydrophobic organic contaminants. The mathematical model proposed here would be useful in the design and operation of such organic chemical biodegradation processes on remediation sites.

Capillary Electrophoretic Determination of Self-dimerization Constants of Aromatic Carboxylate and Sulfonate Ions

Self-dimerizations of twenty three aromatic carboxylate and sulfonate ions from their electrophoretic mobilities in aqueous solution were estimated by capillary zone electrophoresis (CZE). The magnitudes of the self-dimerizations ascribed to pi-pi interactions of these aromatic anions were determined by CZE as dimerization constants (KD). Although the largest KD value of 1.2 dm3 mol(-1) for 9-anthracenecarboxylate ion (9-AC) in these aromatic anions was found, almost all of the KD values were zero, or near to zero. It was found that the pi-pi interactions of the aromatic anions were relatively small at zero ionic strength, in which the contribution of an ionic association between the cation and aromatic anions could be excluded from the KD values, since the contribution of the electric repulsion between the aromatic anions on the KD values was large. The relatively large KD value of 9-AC caused that it electro-migrates as its planar shape, and has an anthracene ring of a largely hydrophobic aromatic ring.