Partitioning of hydrophobic organic compounds within soil-water-surfactant systems

Understanding the partitioning of hydrophobic organic compounds (HOCs) within soil-water-surfactant systems is key to improving the use of surfactants for remediation. The overall objective of this study was to investigate the soil properties that influence the effectiveness of surfactants used to remediate soil contaminated with hydrophobic pesticides, as an example of a more general application for removing strongly sorbing HOCs from contaminated soils via in-situ enhanced sorption, or ex-situ soil washing. In this study, the partitioning of two commonly used pesticides, atrazine and diuron, within soil-water-surfactant systems was investigated. Five natural soils, one nonionic surfactant (Triton-100 (TX)) and one cationic surfactant (benzalkonium chloride (BC)) were used. The results showed that the cation exchange capacity (CEC) is the soil property that controls surfactant sorption onto the soils. Diuron showed much higher solubility enhancement than atrazine with the micelles of either surfactant. Within an ex-situ soil washing system, TX is more effective for soils with lower CEC than those with higher CEC. Within an in-situ enhanced sorption zone, BC works significantly better with more hydrophobic HOCs. The HOC sorption capacity of the sorbed surfactant (K(ss)) was a non-linear function of the amount of surfactant sorbed. For the cationic surfactant (BC), the maximal K(ss) occurred when around 40% of the total CEC sites in the various soils were occupied by sorbed surfactant. Below a sub-saturation sorption range (~20 g/kg), under the same amount of BC sorbed, a soil with lower CEC tends to have higher K(ss) than the one with higher CEC.     

Sorption and desorption of atrazine and diuron onto water dispersible soil primary size fractions

In this study, a low energy separation method was employed to separate water dispersible clay-, silt-, and sand-sized fractions. The batch equilibrium method was used to conduct atrazine and diuron sorption/desorption experiments with the bulk soils and their size fractions separately. A Freundlich sorption model provided the best fit for all sorption and desorption data. A mass balance calculation, taking into account the pesticide concentration differences in the size fraction and bulk soil, showed that pesticide sorption onto the different size fractions reproduces well the total amount of the pesticide sorbed onto the bulk soils. Due to their higher soil organic carbon content, the clay fractions were much more effective sorbents for the pesticides than the bulk soils, silt, and sand fractions. For all soils, the amount of the pesticide sorbed onto the clay fractions was more than 20% of the total amount of the pesticide sorbed by the bulk soils even though the clay fractions in these soils were only 5.3-14.0% (by weight). The clay fractions had the highest desorption hysteresis among all size fractions and the bulk soils, followed by silt fractions, implying the clay fractions had the strongest bound and least desorbable pesticide molecules. Our results suggest that attention should be paid to the pesticide sorbed to the smallest colloids, the water dispersible fraction, which can be potentially mobilized under field conditions, leading to wide spreading of contamination.     

Partitioning of hydrophobic pesticides within a soil-water-anionic surfactant system

Surfactants can be added to pesticide-contaminated soils to enhance the treatment efficiency of soil washing. Our results showed that pesticide (atrazine and diuron) partitioning and desorbability within a soil-water-anionic surfactant system is soil particle-size dependent and is significantly influenced by the presence of anionic surfactant. Anionic surfactant (linear alkylbenzene sulphonate, LAS) sorption was influenced by its complexation with both the soluble and exchangeable divalent cations in soils (e.g. Ca²⁺, Mg²⁺). In this study, we propose a new concept: soil system hardness which defines the total amount of soluble and exchangeable divalent cations associated with a soil. Our results showed that anionic surfactant works better with soils having lower soil system hardness. It was also found that the hydrophobic organic compounds (HOCs) sorbed onto the LAS-divalent cation precipitate, resulting in a significant decrease in the aqueous concentration of HOC. Our results showed that the effect of exchangeable cations and sorption of HOC onto the surfactant precipitates needs to be considered to accurately predict HOC behavior within soil-water-anionic surfactant systems.     

非饱和重塑土的干燥收缩试验研究

基质吸力和净平均应力的增大均可引起土体的压缩变形。针对砂土、粉土、黏土和软土4种不同类型土体,结合试样收缩曲线和土水特征曲线分析了土体干燥过程中基质吸力和孔隙比的关系。试验结果表明:土体干燥收缩过程中随着基质吸力的增大试样不断发生收缩,当基质吸力增大到某特定值时,基质吸力的增大对试样收缩变形无明显影响,称此基质吸力为缩限吸力。屈服吸力s0和缩限吸力ss将试样收缩过程分为弹性阶段、弹塑性阶段和缩限阶段3个阶段。并且不同类型土体的缩限吸力不相同,缩限吸力值与土体的塑性指数密切相关。在干燥收缩过程中,当试样的饱和度减小到90%时试样完成了绝大部分收缩,当试验饱和度达到70%时土样的孔隙比基本保持不变。     

Sorption and desorption of pyridine-clay in aqueous solution

Sterile, radiochemical procedures were applied in a study of the cationic exchange processes occurring during pyridine sorption onto highly-purified sodium kaolinite and sodium montmorillonite particulates of colloidal dimensions. Sodium desorption is directly related to increased protonation. Hydrogen ion exchange dominates at pH < 3. Maximum pyridium sorption occurs at pH 4.0–5.5. At pH > 7.0 neither pyridium nor hydrogen exchange occurs. Previously sorbed pyridium desorbs from the clays as a function of time and solution pH with maximum desorption at pH 1 and 11 and minimum near pH = pK_a = 5.25. Pyridine desorption is much slower than sorption at comparable pH and clay:organic ratio. The extent of desorption is also directly related to the number of stages and/or the volume of solution. Particulate charge, zeta potential, changes are greatest between pH 1–4 with coagulation and charge reversal at pH ≅ 2 if the pyridine concentration is < cation exchange capacity, CEC. Pyridine concentration in excess of CEC induces coagulation through the “cage effect”.     

Influence of ionic surfactants on the flocculation and sorption of palladium and mercury in the aquatic environment

The influence of sub-micellar concentrations of an anionic surfactant (sodium dodecyl sulphate; SDS) and a cationic surfactant (hexadecyl trimethylammonium bromide; HDTMA) on the aquatic behaviour of the strongly complexing metals, Pd(II) and Hg(II), has been investigated. In river water, flocculation of organic complexes of metal was suppressed by SDS but accentuated by HDTMA, effects that are consistent with electrostatic and hydrophobic interactions between ionic surfactants and natural polyelectrolytes. In sea water, flocculation of metal complexes was enhanced by both surfactants because of the shielding and salting effects of inorganic ions on these interactions. Particle surface modification engendered by sorbed surfactant strongly influenced the sorption of Pd and Hg to estuarine particles. Thus, hydrophobically bound SDS enhances the negative charge at the particle surface and favours specific sorption of metal, while specifically sorbed HDTMA enhances the solvency of the particle surface, favouring non-specific sorption of metal complexes. Given the relatively short environmental half-life of SDS, its impacts on strongly complexing metals are predicted to be localised. However, greater stability of HDTMA suggests that its effects on such metals, including enhanced flocculation and sorption, are likely to be more pervasive.     

黏粒和粉粒的共存对砂土静动力液化影响的试验研究

为了研究黏粒、粉粒与砂粒共存的土体中,黏粒和粉粒对砂土抗液化的影响规律,通过静力与动力三轴仪试验系统,对细粒(黏粒和粉粒)含量FC为5%和10%、三种不同细粒配比的试样进行静力与动力三轴试验。试验结果表明:相同细粒含量、不同细粒配比试样的抗液化强度不同;当细粒含量不同时,随着细粒中黏粒或粉粒含量的单调变化,试样所表现出的抗液化规律不同;FC=10%试样的抗液化强度整体高于FC=5%试样的相应强度。随着细粒含量及细粒中黏粒与粉粒相对含量的变化,黏粒与粉粒对砂粒的填充、黏结与骨架作用所占比例不同。     

Geotechnical properties and microstructure of lime-stabilized silt clay

The geotechnical properties and microstructures of lime-stabilized silt clay from Jilin province, China, were studied in detail. Laboratory tests were conducted to evaluate the effects of lime content and curing time on the overall soil properties, including compaction characteristics, Atterberg limits, particle size distribution, pH, stress–strain behavior, peak strength, shear strength parameters, and California bearing ratio (CBR). The stabilized mechanisms of lime in silt clay were examined, and the observed test results were explained based on the results of scanning electron microscropy (SEM) and X-ray diffraction analyses of the specimens. Lime content and curing duration significantly influenced the geotechnical properties and microstructure of the lime-stabilized silt clay specimens. An increase in lime content resulted in increases in compaction water content, liquid limit, plastic limit, sand size-fractions, pH, peak strength, cohesion, internal friction angle, and the CBR, but led to a reduction in the plasticity index, silt fractions, clay fractions, swelling capacity, and water absorption. Also, the addition of lime to silt clay changed this soil type from a ductile to a brittle material. The optimum lime content of the silt clays from Jilin province was determined to be approximately 5–7%. SEM micrographs showed that a white cementitious gel was formed after the addition of lime and that peaks related to smectite, illite, kaolinite, and quartz appeared to be sharper after stabilization with lime and a 90-day period of curing. These results show that the geotechnical properties of lime-stabilized silt clay are affected by the microstructural organization of the silt clay itself.

     

Sorption of dyes from aqueous solutions onto fly ash

Brown coal fly ashes were tested as potentially low-cost sorbents for the removal of synthetic dyes from waters. It was shown that both basic (cationic) as well as acid (anionic) dyes can be sorbed onto the fly ash. The adsorption can be described by the multi-site Langmuir isotherm. The sorption capacities were in the range of 10⁻¹–10⁻³ mmol/g and did not differ significantly for basic and acid dyes. The dye sorption decreased in the presence of organic solvents (methanol, acetone). The presence of oppositely charged surfactants exhibited a pronounced effect on the dye sorption—low concentrations of the surfactant enhanced sorption, whereas high concentrations solubilized the dyes and kept them in solution. Inorganic salts exhibited only a minor effect on the dye sorption. The sorption of basic dyes increased at high pH values, whereas the opposite was true for acid dyes.     

Relationship between mobility factors (Rf) of two hydrophobic termiticides and selected field and artificial soil parameters

Mobility of two commonly used hydrophobic termiticides, chlorpyrifos and fenvalerate, was carried out by soil thin layer chromatograph using 3 field soils and 7 artificial soil as absorbent phases. Mobility factors (R(f)) were measured, and single- and multi-variable linear regression equations were then established. The result indicated that chlorpyrifos removed faster than fenvalerate in both field and artificial soils. In field soils negative correlation coefficients (r) was found between R(f) and organic matter (OM) content, pH, cationic exchange capacity (CEC), and clay content. It was noticeable, however, that correlation coefficient (r) derived from single-variable equations were not a reliable criterion for evaluation of relative importance of individual soil parameter in R(f) determination. One could see, in multi-variable regression, a functional superposition of OM and CEC in pesticide/soil interaction, and the influence of soil pH was overwhelmed by joint action of the other 3 parameters. R(f) of the two hydrophobic termiticides could therefore be predicted with adequate accuracy by either of the combinations of the two parameter: 1) OM content and clay content, 2) CEC and clay content. Introducing field soil properties into equations established from artificial soils one could see that the four-variable equations, which toke sphagnum as the only source of CEC, gave better prediction of field soil R(f). In spite of that these equations were different in two points with those from field soils: Firstly the parameter of soil pH could not be deprived, and secondly, R(f) of chlorpyrifos was positively correlated with the level of clay content.     

Study of pyrene biodegradation capacity in two types of solid media

Removal of pyrene, a representative PAH, was studied using laboratory tests in two different types of solid media: an organic matter collected on the surface of a vertical flow constructed wetland (VFCW) and a formulated clay silicate sand (inorganic matter). The aim of this study was to evaluate the capacity of pyrene biodegradation in these media in order to use them for treating run-off water. The sorption process, the kinetics of pyrene biodegradation and the influence of selected bacteria were also investigated. The sorption process was evaluated by adsorption isotherms and desorption kinetics using a batch equilibration method. The adsorption coefficient values of 28.8 and 2.1 for the organic and the inorganic matter respectively, confirmed the relationship of adsorption with organic carbon content. A small proportion of the sorbed pyrene was available for desorption (8% and 15% for the organic and the inorganic matter, respectively), indicating that sorption was partially irreversible, with the presence of hysteresis. For the formulated clay silicate sand inoculated with a specific bacteria (Mycobacterium sp.6PY1), selected for its ability to degrade PAHs, pyrene removal was complete in 32 days. With the organic matter, these values ranged from 40% to 95% for the different experiments, following a lag time of 3 weeks before observation of a significant degradation. Indigenous bacterial species in the organic medium had the metabolic capacity to degrade pyrene, and microbial populations pre-exposed to the PAH degraded pyrene faster than similar unexposed populations. Three metabolites of pyrene degradation by Mycobacterium were found. They accumulated in both organic and inorganic matter, indicating that the enzymes catalyzing them have slow kinetics.     

苏州第四纪沉积土动剪切模量比和阻尼比试验研究

通过深入分析苏州第四纪土的海相、陆相沉积环境及土层分布特征, 对苏州第四纪土 311 个原状土样进行了土的动剪切模量比和阻尼比试验研究 ,结果发现：海侵作用和土层深度对苏州第四纪各类土的动剪切模量比、阻尼比与剪应变幅值关系曲线的影响有明显差异,深度 0 ～ 30 m 的海相黏土动剪切模量比和阻尼比曲线分别低于和高于陆相黏土的曲线,深度 30 ～ 100 m 的海相黏土动剪切模量比和阻尼比曲线分别高于和低于陆相黏土的曲线;土 层深度对海相黏土、粉质黏土和海、陆相粉细砂的动剪切模量比曲线 以及对海相黏土、粉质黏土和陆相粉细砂的阻尼比曲线的影响较为明显;对黏土、粉质黏土、粉土、粉细砂按土层深度 0 ～ 30 m 和 30 ～ 100 m 以及淤泥质土、中粗砂不区分土层深度,给出了苏州第四纪各类土的动剪切模量比和阻尼比曲线经验关系的拟合参数值及其平均关系曲线推荐值。     

Effect of soil composition and dissolved organic matter on pesticide sorption

The effect of the solid and dissolved organic matter fractions, mineral composition and ionic strength of the soil solution on the sorption behaviour of pesticides were studied. A number of soils, chosen so as to have different clay mineral and organic carbon content, were used to study the sorption of the pesticides atrazine (6-chloro-N2-ethyl-N4-isopropyl-1,3,5-triazine-2,4-diamine), 2,4-D ((2,4-dichlorophenoxy)acetic acid), isoproturon (3-(4-isopropylphenyl)-1,1-dimethylurea) and paraquat (1,1'-dimethyl-4,4'-bipyridinium) in the presence of low and high levels of dissolved organic carbon and different background electrolytes. The sorption behaviour of atrazine, isoproturon and paraquat was dominated by the solid state soil components and the presence of dissolved organic matter had little effect. The sorption of 2,4-D was slightly affected by the soluble organic matter in the soil. However, this effect may be due to competition for adsorption sites between the pesticide and the soluble organic matter rather than due to a positive interaction between the pesticide and the soluble fraction of soil organic matter. It is concluded that the major factor governing the sorption of these pesticides is the solid state organic fraction with the clay mineral content also making a significant contribution. The dissolved organic carbon fraction of the total organic carbon in the soil and the ionic strength of the soil solution appear to have little or no effect on the sorption/transport characteristics of these pesticides over the range of concentrations studied.     

特殊岩土人工开挖桩板墙桩井的施工

在淤泥质粘土、粉砂层成饱和且在不同涌水量状态下,采取缩短循环开挖深度、回填柔韧性材料、下钢套筒、帷幕注浆等多种施工方案,成功地解决了护壁施工过程中若干工程问题。     

Spatial variability of the soil erodibility parameters and their relation with the soil map at subgroup level

This project takes a look at the variation of the parameters related to soil erodibility (fractions of clay, silt, fine and coarse sand; organic matter, permeability, and structure) coming from soil pits from the Community of Madrid's soil map (Spain), according to Soil Taxonomy at subgroup level. It draws the conclusion that map erodibility shouldn't be estimated from a soil map because the K factor obtained does not present significant differences among the different types of soil. One or more key factors related with soil erodibility must be taken into account if erodibility maps are to be drawn. This research has shown that silt and structure could be considered key factors for erodibility maps of the area, but not significant differences have been found in important factors such as clay or organic matter due to the wide range of data variance. In order to elaborate erosion risk maps the use of the K factor from the physiographical map is a good alternative. When data are grouped according to these criteria significant differences in K factor are shown. Erodibility was greater in soils developed over gypsic material, with a value of 0.63+/-0.28, than in high plateaus (locally know as alcarrias), with a value of 0.40+/-0.18. In order to adequately represent soil erodibility, a kriging geostatistic technique is used, which reduces the variation of the factors considered when they are found to correlate, as is the case with the parameters considered to calculate K factor.     

Degradation of soil-sorbed trichloroethylene by stabilized zero valent iron nanoparticles: effects of sorption, surfactants, and natural organic matter

Zero valent iron (ZVI) nanoparticles have been studied extensively for degradation of chlorinated solvents in the aqueous phase, and have been tested for in-situ remediation of contaminated soil and groundwater. However, little is known about its effectiveness for degrading soil-sorbed contaminants. This work studied reductive dechlorination of trichloroethylene (TCE) sorbed in two model soils (a potting soil and Smith Farm soil) using carboxymethyl cellulose (CMC) stabilized Fe-Pd bimetallic nanoparticles. Effects of sorption, surfactants and dissolved organic matter (DOC) were determined through batch kinetic experiments. While the nanoparticles can effectively degrade soil-sorbed TCE, the TCE degradation rate was strongly limited by desorption kinetics, especially for the potting soil which has a higher organic matter content of 8.2%. Under otherwise identical conditions, ∼44% of TCE sorbed in the potting soil was degraded in 30 h, compared to ∼82% for Smith Farm soil (organic matter content = 0.7%). DOC from the potting soil was found to inhibit TCE degradation. The presence of the extracted SOM at 40 ppm and 350 ppm as TOC reduced the degradation rate by 34% and 67%, respectively. Four prototype surfactants were tested for their effects on TCE desorption and degradation rates, including two anionic surfactants known as SDS (sodium dodecyl sulfate) and SDBS (sodium dodecyl benzene sulfonate), a cationic surfactant hexadecyltrimethylammonium (HDTMA) bromide, and a non-ionic surfactant Tween 80. All four surfactants were observed to enhance TCE desorption at concentrations below or above the critical micelle concentration (cmc), with the anionic surfactant SDS being most effective. Based on the pseudo-first-order reaction rate law, the presence of 1×cmc SDS increased the reaction rate by a factor of 2.5 when the nanoparticles were used for degrading TCE in a water solution. SDS was effective for enhancing degradation of TCE sorbed in Smith Farm soil, the presence of SDS at sub-cmc increased TCE degraded by ∼10%. However, effect of SDS on degradation of TCE in the potting soil was more complex. The presence of SDS at sub-cmc decreased TCE degradation by 5%, but increased degradation by 5% when SDS dosage was raised to 5×cmc. The opposing effects were attributed to combined effects of SDS on TCE desorption and degradation, release of soil organic matter and nanoparticle aggregation. The findings strongly suggest that effect of soil sorption on the effectiveness of Fe-Pd nanoparticles must be taken into account in process design, and soil organic content plays an important role in the overall degradation rate and in the effectiveness of surfactant uses.     

基于 EVD 的一种高速公路路基压实度快速检测方法研究

路基的压实质量直接决定路基承载能力和抗变形能力,也同时影响道路的服务水平和使用寿命。传统的路基压实度采用环刀法、灌砂法、灌水法等,其操作复杂、投入人力多、测试时间长。本文将便携式动态变形模量测试仪(LFGpro)测得的动态变形模量(EVD)与压实度(K)之间建立相关关系,从而快速、高效的得到路基的压实度。本文分别建立了黄土(低液限粉土ML)、红砂岩(黏土质砂)、红泥岩(高液限黏土CH)路基EVD与K之间的相关关系,相关性良好。     

Partitioning of hydrophobic organic chemicals (HOC) into anionic and cationic surfactant-modified sorbents

Surfactant-modified sorbents have been proposed for the removal of organic compounds from aqueous solution. In the present study, one cationic (HDTMA) and three anionic (DOWFAX-8390, STEOL-CS330, and Aerosol-OT) surfactants were tested for their sorptive behavior onto different sorbents (alumina, zeolite, and Canadian River Alluvium). These surfactant-modified materials were then used to sorb a range of hydrophobic organic chemicals (HOCs) of varying properties (benzene, toluene, ethylbenzene, 1,2-dichlorobenzene, naphthalene, and phenanthrene), and their sorption capacity and affinity (organic-carbon-normalized sorption coefficient, K(oc)) were quantified. The HDTMA-zeolite system proved to be the most stable surfactant-modified sorbent studied because of the limited surfactant desorption. Both anionic and cationic surfactants resulted in modified sorbents with higher sorption capacity and affinity than the unmodified Canadian River Alluvium containing only natural organic matter. The affinities of the surfactant-modified sorbents (K(oc)) for most HOCs are lower than octanol/water partition coefficient (K(ow)) normalized to the organic carbon content (f(oc)) and the density of octanol (K(oc) octanol); naphthalene and phenanthrene are the exceptions to this rule.     

A shift in pathway of iron-mediated perchloroethylene reduction in the presence of sorbed surfactant--a column study

Surface modification of zero-valent iron (ZVI) to enhance its reduction rates for chlorinated ethanes and ethenes has recently attracted great attention. In this research, the enhancement of perchloroethylene (PCE) reduction by ZVI in the presence of sorbed micelles of the cationic surfactant hexadecyltrimethylammonium (HDTMA) was examined in a series of laboratory column tests with varying flow rates and input PCE concentrations. Model simulations using HYDRUS-1D showed that the overall pseudo first-order rate constants for PCE reduction by ZVI increased by a factor of four in the presence of sorbed HDTMA admicelles. The increase in reduction rate was attributed to a higher distribution coefficient (K_d) for contaminant sorption on surfactant-modified ZVI (SM-ZVI) compared to untreated ZVI. Modeling results also showed that in the presence of HDTMA admicelles 58–100% of PCE reduction occurred via hydrogenolysis. In contrast, only 12–25% PCE underwent hydrogenolysis when HDTMA was absent. The significant increase in TCE production during PCE reduction by SM-ZVI verified a shift in reaction pathway previously observed in batch studies, most likely from β-elimination to hydrogenolysis. Although this shift in reaction pathway resulted in a higher accumulation of TCE, the combined concentrations of chlorinated hydrocarbons in the effluent were 1.5–5 times lower when SM-ZVI rather than unmodified ZVI was used.     

Mineralization of a sorbed polycyclic aromatic hydrocarbon in two soils using catalyzed hydrogen peroxide

Hydrogen peroxide (H2O2) catalyzed by soluble iron or naturally occurring soil minerals, (i.e., modified Fenton's reagent) was investigated as a basis for mineralizing sorbed and NAPL-phase benzo[a]pyrene (BaP), a hydrophobic and toxic polycyclic aromatic hydrocarbon, in two soils of different complexity. 14C-Benzo[a]pyrene was added to silica sand and a silt loam soil, and mineralization was investigated using three-level central composite rotatable experimental designs. The effects of H2O2 concentration, slurry volume, and iron(II) amendment were investigated in the silica sand systems. In a Palouse loess silt loam soil, the variables included H2O2 concentration, slurry volume, and pH, with H2O2 catalyzed by naturally occurring iron oxyhydroxides. Regression equations generated from the data were used to develop three-dimensional response surfaces describing BaP mineralization. Based on the recovery of 14C-CO2, 70% BaP mineralization was achieved in the sand within 24 h using 15 M H2O2 and an iron(II) concentration of 6.6 mM with a slurry volume of 0.3 x the field capacity of the sand. For the silt loam soil, 85% mineralization of BaP was observed using 15 M H2O2, no iron amendment, and a slurry volume of 20 x the soil field capacity. The balance of the radiolabeled carbon remained as unreacted BaP in the soil fraction. Gas-purge measurements over 5 d confirmed negligible desorption under nontreatment conditions. However, oxidation reactions were complete within 24 h and promoted up to 85% BaP mineralization, documenting that the natural rate of desorption/dissolution did not control the rate of oxidation and mineralization of the BaP. The results show that catalyzed H2O2 has the ability to rapidly mineralize sorbed/NAPL-phase BaP and that partitioning, which is often the rate-limiting factor in soil remediation, does not appear to limit the rate of vigorous Fenton-like treatment.