Influence of cation type, ionic strength, and pH on solubilization and mobilization of residual hydrocarbon by a biosurfactant

This study investigated the effect of cation type, ionic strength, and pH on the performance of an anionic monorhamnolipid biosurfactant for solubilization and removal of residual hexadecane from sand. Three common soil cations, Na⁺, Mg²⁺, and Ca²⁺, were used in these experiments and hexadecane was chosen to represent a nonaqueous phase liquid (NAPL) less dense than water. Results showed that hexadecane solubility in rhamnolipid solution was significantly increased by the addition of Na⁺ and Mg²⁺. Addition of up to 0.2 mM Ca²⁺ also increased hexadecane solubility. For Ca²⁺ concentrations greater than 0.2 mM there was little effect on hexadecane solubility due to competing effects of calcium-induced rhamnolipid precipitation and enhanced hexadecane solubilization. Efficiency of NAPL solubilization can be expressed in terms of molar solubilization ratios (MSR). The results showed that MSR values for hexadecane in rhamnolipid solutions increased 7.5-fold in the presence of 500 mM Na⁺, and 25-fold in the presence of 1 mM Mg²⁺. The presence of cations also reduced the interfacial tension between rhamnolipid solutions and hexadecane. For example, an increase in Na⁺ from 0 to 800 mM caused a decrease in interfacial tension from 2.2 to 0.89 dyn cm⁻¹. Similarly, decreasing pH caused a reduction in interfacial tension. The lowest interfacial tension value observed in this study was 0.02 dyn cm⁻¹ at pH 6 in the presence of 320 mM Na⁺. These conditions were also found to be optimal for removal of hexadecane residual from sand columns, with 58% of residual removed within three pore volumes. The removal of residual NAPL from the packed columns was primarily by mobilization, even though solubilization was significantly increased in the presence of Na⁺.     

Different behaviours in the solubilization of polycyclic aromatic hydrocarbons in water induced by mixed surfactant solutions

Water solubility of polycyclic aromatic hydrocarbons (PAHs), viz, naphthalene and phenanthrene, in micellar solutions at 25 °C was investigated, using two series of different binary mixtures of anionic and nonionic surfactants. Tween 80 and Brij-35 were used as nonionic surfactants whereas fatty acids or amphiphilic cyclodextrins (Mod-β-CD) synthesized in our laboratory were used as anionic ones. Solubilization capacity has been quantified in terms of the molar solubilization ratio and the micelle-water partition coefficient, using UV-visible spectrophotometry. Anionic surfactants exhibited less solubilization capacity than nonionics. The mixtures between Tween 80 and Mod-β-CD did not show synergism to increase the solubilization of PAHs. On the other hand, the mixtures formed by Tween 80 and fatty acids at all mole fractions studied produced higher enhancements of the solubility of naphthalene than the individual surfactants. The critical micellar concentration of the mixtures of Tween 80/sodium laurate was determined by surface tension measurements and spectrofluorimetry using pyrene as probe. The system is characterized by a negative interaction parameter (β) indicating attractive interactions between both surfactants in the range of the compositions studied.     

Synergistic solubilization of polycyclic aromatic hydrocarbons by mixed anionic-nonionic surfactants

Water solubility enhancements of naphthalene (Naph), acenaphthylene (Acen), anthracene (An), phenanthrene (Phen) and pyrene (Py) by micellar solutions of single and mixed anionic-nonionic surfactants were measured and compared. Effects of typical inorganic ions, such as NH(4)(+), Na(+) and Mg(2+) coexisted with the organic pollutants (in soils) on water solubilities of polycyclic aromatic hydrocarbons (PAHs) in the presence of single and mixed surfactants were also investigated. Solubilities of PAHs in water are greatly enhanced in a linear fashion by each of Triton X-100 (TX100), Triton X-305 (TX305), Brij 35, and sodium dodecyl sulfate (SDS). Solubility enhancement efficiencies of surfactants above the critical micelle concentration (CMC) follow the order of TX100>Brij 35>TX305>SDS. PAHs are solubilized synergistically in mixed anionic-nonionic surfactant solutions, especially at low surfactant concentrations. The synergistic power of the mixed surfactants is SDS-TX305>SDS-Brij 35>SDS-TX100. Synergistic effect of a given mixed-surfactant solution on different PAHs also appears to be linearly related to the solute logK(ow). The noted synergism for the mixed surfactants is attributed to the formation of mixed micelles, the lower CMC of the mixed-surfactant solutions, and the increase of the solute's molar solubilization ratio or micellar partition coefficients (K(mc)) because of the lower polarity of the mixed micelles. Suitable quantity of inorganic cations can enhance the solubilization capacities of anionic-nonionic mixed surfactants, the effect being Mg(2+)>NH(4)(+)>Na(+). The water solubility of pyrene was slightly increased by anthracene and significantly increased by 1,2,3-TCB in the presence of SDS-Brij 35. Mixed surfactants may improve the performance of surfactant-enhanced remediation of soils and sediments by decreasing the applied surfactant level and thus the remediation cost.     

蓖麻油衍生微乳液对菲的增溶和洗脱作用及其对菲污染土壤的修复机理

比较研究了蓖麻油硫酸盐(SCOS)与普通表面活性剂Triton X-100(TX100)、Tween 80(TW80)、Brij35、十二烷基苯磺酸钠(SDBS)和十二烷基硫酸钠(SDS)等对菲的增溶和洗脱作用.结果表明,菲表观溶解度与SCOS的浓度呈单一线性关系,SCOS微乳液对菲的增溶比SR=0.0314为最大,菲在微乳相和水相之间的分配系数logKem=4.44,大于菲在胶束相和水相之间的分配系数(logKmc).1:10土-水体系下,SCOS微乳液对菲污染土壤的清洗速率最快,清洗效率最高.SCOS有望成为土壤有机污染淋洗修复的增效试剂.     

Removal of vaporous naphthalene using polyoxyethylenated nonionic surfactants

Previous research has demonstrated that an anionic surfactant can increase the solubility of the vapor phases of both naphthalene and sulfur dioxide in water. This study examines the feasibility of removing polycyclic aromatic hydrocarbons (PAHs) during gas absorption by adding the polyoxyethylenated nonionic surfactants tetraethylene glycol monodecyl ether (C10E4), octaethylene glycol monodecyl ether (C10E8), and octaethylene glycol monotetradecyl ether (C14E8), to water. The apparent solubility and absorption rates of naphthalene in surfactant solution were slightly higher than in pure water at a concentration lower than the critical micelle concentration (CMC). However, the apparent equilibrium naphthalene solubility increased linearly in proportion to the concentrations of nonionic surfactants because of the solubilization effect of micelles at concentrations above the CMC. The solubilization effect exceeded that of the reduced mass transfer coefficient, increasing the rate of absorption of vaporous naphthalene. For the four surfactants, the capacity to solubilize naphthalene was in the order C10E4 > C14E8 > C10E8 > sodium dodecyl sulfate (SDS) and was related to the hydrophile-lipophile balance values of the surfactants. The enrichment factors, which can express the degree of naphthalene solubility in solution, were 6.09-14.2 at a surfactant concentration of 0.01 M for the three polyoxyethylenated nonionic surfactants. Empirical findings confirm that adding nonionic surfactants increases the absorption efficiency of hydrophobic organic compounds (HOCs) using spray or packed tower.     

Simultaneous removal of phenanthrene and cadmium from contaminated soils by saponin, a plant-derived biosurfactant

Batch experiments were conducted to evaluate the performance of saponin, a plant-derived biosurfactant, for simultaneously removing phenanthrene and cadmium from the combined contaminated soils. Results showed that phenanthrene was desorbed from the contaminated soils by saponin with the partition of phenanthrene into surfactant micelle, meanwhile cadmium was effectively removed from the contaminated soils by the complexation of cadmium with the external carboxyl groups of saponin micelle. The efficiencies of saponin for the removal of phenanthrene and cadmium from the contaminated soils were greater than that of Triton X100 and citric acid, respectively. At concentration of 3750 mg/L, saponin has a removal rate of 87.7% and 76.2% of cadmium and phenanthrene, respectively, from the combined contaminated soil. The removals of cadmium and phenanthrene from the soils were not obviously constrained each other. Thus, saponin has the potential for the removal of heavy metal and PAHs from the combined contaminated soils.     

甘氨酸-β-环糊精对菲的增溶、解吸行为研究

为改善β-环糊精的水溶性,将β-环糊精和甘氨酸在碱性条件下用环氧氯丙烷连接起来,得到水溶性极好的甘氨酸-β-环糊精,研究了甘氨酸-β-环糊精对菲的增溶、解吸行为,考察了pH、甘氨酸-β-环糊精初始浓度、温度、不同环糊精类型对菲解吸的影响。结果表明,甘氨酸-β-环糊精对菲的增溶效果显著,其初始质量浓度为30 g/L时,对菲的增溶倍数可以达到近30倍;甘氨酸-β-环糊精对菲的解吸随pH的升高而降低;升高甘氨酸-β-环糊精初始浓度和温度有利于菲的解吸;甘氨酸-β-环糊精对菲的解吸好于α-环糊精和β-环糊精,甘氨酸-β-环糊精对菲污染土壤的解吸符合准二级动力学方程。该静态解吸研究可以为菲污染土壤的修复提供基础信息。     

Solubilization of PAH mixtures by three different anionic surfactants

Solubilization of naphthalene and phenanthrene into the micelles formed by three different anionic surfactants was investigated for single, binary, and ternary mixtures including pyrene. The three surfactants were sodium dodecylbenzene sulfonate (SDDBS), monoalkylated disulfonated diphenyl oxide (MADS-C12), and dialkylated disulfonated diphenyl oxide (DADS-C12). The order of increasing solubility enhancement of naphthalene and phenanthrene was SDDBS < MADS-C12 < < DADS-C12, which indicates that the hydrophobic chains in micellar core play more important role for the solubilization of polycyclic aromatic hydrocarbons (PAHs) than the benzene rings in palisade layer of a micelle. The solubility enhancement of naphthalene was slightly changed in PAH mixtures. The solubility of phenanthrene was greatly enhanced in presence of naphthalene but reduced in presence of pyrene. The explanation for these results could be that less hydrophobic compounds can be solubilized at the interfacial region of a hydrophobic core, which reduces the interfacial tension between the core and water, and then the reduced interfacial tension can support a larger core volume for the same interfacial energy.     

PCE solubilization and mobilization by commercial humic acid

In this paper, comparison is made of terms describing solubilization of hydrophobic organic compounds (HOC) by dissolved humic substances (DHS) and commercial non-ionic surfactants. This paper examines the ability of a commercial humic acid (Aldrich humic acid) to solubilize and mobilize tetrachlorothene (PCE) residual in porous media. The constant for solubilization of PCE by Aldrich humic acid is shown to be a factor of two to thirty times less than that published for dodecyl alcohol ethoxylate surfactants, showing that Aldrich humic acid is less capable than some non-ionic surfactants at solubilizing residual PCE. The depression of PCE–water interfacial tension in the presence of DHS is shown to be significantly less than published values for a non-ionic surfactant, and surfactant mixtures, indicating that the DHS used in this study is less prone to cause mobilization of non-aqueous phase liquids relative to surfactants. Several possible advantages of DHS use in the remediation of subsurface media contaminated with HOC are described, including the ability of DHS to solubilize HOC irrespective of the DHS concentration, and potential lesser tendency of DHS to depress the interfacial tension between non-aqueous phases and water relative to surfactants (an advantage when mobilization is undesired).     

Biodegradation of polycyclic aromatic hydrocarbons by a mixed culture

We investigated the potential biodegradation of polycyclic aromatic hydrocarbons (PAHs) by an aerobic mixed culture utilizing phenanthrene as its carbon source. Following a 3-5 h post-treatment lag phase, complete degradation of 5 mg/l phenanthrene occurred within 28 h (optimal conditions determined as 30 degrees C and pH 7.0). Phenanthrene degradation was enhanced by the individual addition of yeast extract, acetate, glucose or pyruvate. Results show that the higher the phenanthrene concentration, the slower the degradation rate. While the mixed culture was also capable of efficiently degrading pyrene and acenaphthene, it failed to degrade anthracene and fluorene. In samples containing a mixture of the five PAHs, treatment with the aerobic culture increased degradation rates for fluorene and anthracene and decreased degradation rates for acenaphthene, phenanthrene and pyrene. Finally, it was observed that when nonionic surfactants were present at levels above critical micelle concentrations (CMCs), phenanthrene degradation was completely inhibited by the addition of Brij 30 and Brij 35, and delayed by the addition of Triton X100 and Triton N101.     

Solubilization and biodegradation of phenanthrene in mixed anionic-nonionic surfactant solutions

The effects of mixed anionic-nonionic surfactants, sodium dodecyl sulfate (SDS) mixed with Tween80 (TW80), Triton X-100 (TX100) and Brij35 respectively on the solubility enhancement and biodegradation of phenanthrene in the aqueous phase were investigated. The efficiency of solubilization and biodegradation of phenanthrene in single-, and mixed-surfactant solutions were also compared. The critical micellar concentrations (CMCs) of mixed surfactants were sharply lower than that of sole SDS. The degree of solubility enhancements by the mixed surfactants followed the order of SDS-TW80>SDS-Brij35>SDS-TX100. Synergistic solubilization was observed in the mixed surfactant solutions, in which the molar ratios of SDS to nonionic surfactant were 1:0, 9:1, 7:3, 5:5, 3:7, 1:9 and 0:1 while the total concentration of surfactants was kept at 5.0 and 10.0 mM, respectively. SDS-Brij35 exhibited more significant degree of synergistic solubility enhancement for phenanthrene. The mixed surfactants exhibited no inhibitory effect on biodegradation of phenanthrene. Substantial amounts of the solubilized phenanthrene by mixed surfactants were completely degraded by phenanthrene-degrading microorganisms within 96 h. The results suggested that anionic-nonionic surfactants would improve the performance of remediation of PAH-contaminated soils.     

Simultaneous removal of organic compounds and heavy metals from soils by electrokinetic remediation with a modified cyclodextrin

Thousands of sites are contaminated with both heavy metals and organic compounds and these sites pose a major threat to public health and the environment. Previous studies have shown that electrokinetic remediation has potential to remove heavy metals and organic compounds when they exist individually in low permeability soils. This paper presents the feasibility of using cyclodextrins in electrokinetic remediation for the simultaneous removal of heavy metals and polycyclic aromatic hydrocarbons (PAHs) from low permeability soils. Kaolin was selected as a model low permeability soil and it was spiked with phenanthrene as well as nickel at concentrations of 500 mg kg-1 each to simulate typical mixed field contamination. Bench-scale electrokinetic experiments were conducted using hydroxypropyl beta-cyclodextrin (HPCD) at low (1%) and high (10%) concentrations and using deionized water in control test. A periodic voltage gradient of 2VDC cm-1 (with 5 d on and 2 d off) was applied to all the tests, and 0.01 M NaOH was added during the experiments to maintain neutral pH conditions at anode. In all tests, nickel migrated as Ni2+ ions towards the cathode and most of it was precipitated as Ni(OH)2 within the soil close to the cathode due to high pH condition generated by electrolysis reaction. The solubility of phenanthrene in the flushing solution and the amount of electroosmotic flow controlled the migration and removal of phenanthrene in all the tests. Even though high flow was generated in tests using deionized water and 1% HPCD, migration and removal of phenanthrene was low due to low solubility of phenanthrene in these solutions. The test with 10% HPCD solution showed higher solubility of phenanthrene which caused it migrate towards the cathode, but further migration and removal was retarded due to reduced electric current and electroosmotic flow. Approximately one pore volume of flushing resulted in approximately 50% removal of phenanthrene from the soil near the anode. Sustained higher electroosmotic flow with higher concentration cyclodextrin and maintaining low soil pH near cathode should be investigated to increase removal efficiency of both phenanthrene and nickel.     

Enhancement of phenanthrene adsorption on a clayey soil and clay minerals by coexisting lead or cadmium

Phenanthrene is commonly present together with heavy metals at many contaminated sites. This study investigated the influence of coexisting lead (Pb²⁺) or cadmium (Cd²⁺) on phenanthrene adsorption on soils. Batch experiments were conducted under different geochemical conditions including pH, mineral structure, organic matter content, and varying amounts of heavy metals. The results showed that the presence of heavy metals in solution at a fixed pH of 5.8 ± 0.1 enhanced phenanthrene adsorption, the extent of which was closely related to the concentrations and the electro-negativity of the metals. The enhancement on phenanthrene adsorption was positively correlated to the amount of adsorbed metals. Although Cd²⁺ is a softer Lewis acid, Pb²⁺ displayed a more significant effect as it was adsorbed to a greater extent on the soil surfaces. Thus, density of cation accumulation appears to be more influential than metal softness in enhancing phenanthrene adsorption. Moreover, with a portion of organic matter removed by heating at 550 °C, there was a stronger enhancement of phenanthrene adsorption by coexisting Pb²⁺, indicating an increasingly dominant mechanisms associated with Pb²⁺ at a lower organic matter content. Similar enhancement phenomenon was observed on bentonite and kaolinite, probably resulting from the cation-π bonding between the adsorbed soft metal cations and the aromatic ring of phenanthrene in solution. The desorption experiments further suggested that the bonding of phenanthrene adsorption was strengthened in the presence of Pb²⁺ and that a larger proportion of adsorbed phenanthrene remained on the soils (residual fraction) even after sequential methanol extractions. Further spectroscopic analyses and surface characterization are required to provide direct evidence of the formation and relative significance of cation-π bond for phenanthrene adsorption.     

Reducing plant uptake of PAHs by cationic surfactant-enhanced soil retention

Reducing the transfer of contaminants from soils to plants is a promising approach to produce safe agricultural products grown on contaminated soils. In this study, 0-400 mg/kg cetyltrimethylammonium bromide (CTMAB) and dodecylpyridinium bromide (DDPB) were separately utilized to enhance the sorption of PAHs onto soils, thereby reducing the transfer of PAHs from soil to soil solution and subsequently to plants. Concentrations of phenanthrene and pyrene in vegetables grown in contaminated soils treated with the cationic surfactants were lower than those grown in the surfactant-free control. The maximum reductions of phenanthrene and pyrene were 66% and 51% for chrysanthemum (Chrysanthemum coronarium L.), 62% and 71% for cabbage (Brassica campestris L.), and 34% and 53% for lettuce (Lactuca sativa L.), respectively. Considering the impacts of cationic surfactants on plant growth and soil microbial activity, CTMAB was more appropriate to employ, and the most effective dose was 100-200 mg/kg.     

Influence of a large steel complex on the spatial distribution of volatile polycyclic aromatic hydrocarbons (PAHs) determined by passive air sampling using membrane-enclosed copolymer (MECOP)

Membrane-enclosed copolymer (MECOPs) samplers containing crystalline copolymers of ethylvinylbenzene-divinylbenzene in polyethylene membranes were used to assess the influence of a steel complex on the level and spatial distribution of polycyclic aromatic hydrocarbons (PAHs) in ambient air. MECOPs were deployed at six sites in Pohang, Korea for 37 days (August 9, 2005–September 14, 2005). Fluorene, phenanthrene, anthracene, and fluoranthene were dominant PAHs with the highest contribution of phenanthrene (59%) to the total amount of vapor-phase PAHs. The spatial distribution of total PAHs in the vapor phase ranging from 76 to 1077 ng MECOP⁻¹ and air dispersion modeling suggested that the steel complex was the major PAH source in Pohang. It was revealed that the major wind directions rather than the distance from the steel complex were a significant factor affecting the levels of PAHs at the sampling sites. Finally, we tried to convert MECOP concentrations (ng MECOP⁻¹) to air concentrations (ng m⁻³) with the modified sampling rates (m³ day⁻¹). This study demonstrates again that passive air samplers are useful tools for spatially resolved and time-integrated monitoring of semivolatile organic compounds (SOCs) in ambient air.     

Enhanced desorption of phenanthrene from contaminated soil using anionic/nonionic mixed surfactant

A new approach using an anionic/nonionic mixed surfactant, sodium dodecyl sulphate (SDS) with Triton X-100 (TX100), was utilized for the desorption of phenanthrene from an artificial contaminated natural soil in an aim to improve the efficiency of surfactant remediation technology. The experimental results showed that the presence of SDS not only reduced the sorption of TX100 onto the natural soil, but also enhanced the solubilization of TX100 for phenanthrene, both of which resulted in the distribution of phenanthrene in soil-water systems decreasing with increasing mole fraction of SDS in surfactant solutions. These results can be attributed to the formation of mixed micelles in surfactant solution and the corresponding decrease in the critical micelle concentration of TX100 in mixed solution. The batch desorption experiments showed that the desorption percentage of phenanthrene from the contaminated soil with mixed solution was greater than that with single TX100 solution and appeared to be positively related to the mole fraction of SDS in surfactant solution. Thus, the anionic/nonionic mixed surfactants are more effective for the desorption of phenanthrene from the contaminated soil than a single nonionic surfactant.     

Solubilization, solution equilibria, and biodegradation of PAH's under thermophilic conditions

Biodegradation rates of PAHs are typically low at mesophilic conditions and it is believed that the kinetics of degradation is controlled by PAH solubility and mass transfer rates. Solubility tests were performed on phenanthrene, fluorene and fluoranthene at 20 degrees C, 40 degrees C and 60 degrees C and, as expected, a significant increase in the equilibrium solubility concentration and of the rate of dissolution of these polycyclic aromatic hydrocarbons (PAHs) was observed with increasing temperature. A first-order model was used to describe the PAH dissolution kinetics and the thermodynamic property changes associated with the dissolution process (enthalpy, entropy and Gibb's free energy of solution) were evaluated. Further, other relevant thermodynamic properties for these PAHs, including the activity coefficients at infinite dilution, Henry's law constants and octanol-water partition coefficients, were calculated in the temperature range 20-60 degrees C. In parallel with the dissolution studies, three thermophilic Geobacilli were isolated from compost that grew on phenanthrene at 60 degrees C and degraded the PAH more rapidly than other reported mesophiles. Our results show that while solubilization rates of PAHs are significantly enhanced at elevated temperatures, the biodegradation of PAHs under thermophilic conditions is likely mass transfer limited due to enhanced degradation rates.     

Evaluation of in situ catalysed hydrogen peroxide propagation (CHP) for phenanthrene and fluoranthene removals from soil and its associated impacts on soil functionality

Extensive contamination of soils by highly recalcitrant contaminants such as polycyclic aromatic hydrocarbons (PAHs) is an environmental problem arising from rapid industrialisation. This work focusses on the remediation of soil contaminated with 3- and 4-aromatic ring PAHs (phenanthrene (PHE) and fluoranthene (FLUT)) through catalysed hydrogen peroxide propagation (CHP). In the present work, the operating parameters of the CHP treatment in packed soil column was optimised with central composite design (H₂O₂/soil 0.081, Fe³⁺/soil 0.024, sodium pyrophosphate (SP)/soil 0.024, pH of SP solution 7.73). The effect of contaminant aging on PAH removals was also investigated. Remarkable oxidative PAH removals were observed for the short aging and extended aging period (up to 86.73 and 70.61 % for PHE and FLUT, respectively). The impacts of CHP on soil biological, chemical and physical properties were studied for both spiked and aged soils. Overall, the soil functionality analyses after the proposed operating condition demonstrated that the values for soil respiration, electrical conductivity, pH and iron precipitation fell within acceptable limits, indicating the compatibility of the CHP process with land restoration.