Modeling the two stages of surfactant-aided soil washing

Surfactant-enhanced aquifer remediation: Mechanisms, influences, limitations and the countermeasures

In recent years, surfactant-enhanced aquifer remediation (SEAR) has attracted increasing interest duo to the high efficiency of removing non-aqueous phase liquids (NAPLs) from aquifer. A thorough understanding of SEAR is necessary for its successful implementation in field remediation. This paper reviewed the SEAR technology in a comprehensive way based on the recent research advances. Firstly, an overview of the basic processes and mechanisms underlying the technology was presented. Secondly, applications of SEAR and the factors that influence the performance were summarized. Thirdly, the key limitations of SEAR, which are downward migration of dense-NAPLs, secondary pollution of surfactants, adsorptive, precipitative and partitioning loss of surfactants, and heterogeneity of the aquifer, were reviewed. Finally, the recent advances in modifying SEAR to overcome the limitations were discussed in detail. The review will promote our understanding of SEAR technology and provide some useful information to improve the performance of SEAR in applications.

The flotation and adsorption of mixed collectors on oxide and silicate minerals

The analysis of flotation and adsorption of mixed collectors on oxide and silicate minerals is of great importance for both industrial applications and theoretical research. Over the past years, significant progress has been achieved in understanding the adsorption of single collectors in micelles as well as at interfaces. By contrast, the self-assembly of mixed collectors at liquid/air and solid/liquid interfaces remains a developing area as a result of the complexity of the mixed systems involved and the limited availability of suitable analytical techniques. In this work, we systematically review the processes involved in the adsorption of mixed collectors onto micelles and at interface by examining four specific points, namely, theoretical background, factors that affect adsorption, analytical techniques, and self-assembly of mixed surfactants at the mineral/liquid interface. In the first part, the theoretical background of collector mixtures is introduced, together with several core solution theories, which are classified according to their application in the analysis of physicochemical properties of mixed collector systems. In the second part, we discuss the factors that can influence adsorption, including factors related to the structure of collectors and environmental conditions. We summarize their influence on the adsorption of mixed systems, with the objective to provide guidance on the progress achieved in this field to date. Advances in measurement techniques can greatly promote our understanding of adsorption processes. In the third part, therefore, modern techniques such as optical reflectometry, neutron scattering, neutron reflectometry, thermogravimetric analysis, fluorescence spectroscopy, ultrafiltration, atomic force microscopy, analytical ultracentrifugation, X-ray photoelectron spectroscopy, Vibrational Sum Frequency Generation Spectroscopy and molecular dynamics simulations are introduced in virtue of their application. Finally, focusing on oxide and silicate minerals, we review and summarize the flotation and adsorption of three most widely used mixed surfactant systems (anionic-cationic, anionic-nonionic, and cationic-nonionic) at the liquid/mineral interface in order to fully understand the self-assembly progress. In the end, the paper gives a brief future outlook of the possible development in the mixed surfactants.

Photodegradation of 4,4'-dibrominated diphenyl ether in Triton X-100 micellar solution

This study has investigated the photochemical reactions of 4,4'-dibrominated diphenyl ether (BDE-15) in Triton X-100 (TX-100) solution by UV light. All photolysis experiments were performed in TX-100 solutions which were all above critical micelle concentration (CMC). BDE-15 photodegradation follows the pseudo-first-order kinetics under various conditions. The results showed that the degradation rates of BDE-15 increased with the increasing concentration of TX-100, and decreased when TX-100 was used in excess, because TX-100 can act as hydrogen donor, photosensitizer and light barrier. When the pH value was in the range of 1-11, the degradation rates increased with the increasing pH value due to the proton effect and free radical reaction. When pH reached 13, the corresponding degradation rate dropped significantly, which was attributed to the decreasing surface potential of micellar retarding the degradation process. BDE-15 was debrominated into 4-dibrominated diphenyl ether (BDE-3) and diphenyl ether (DE), subsequently. In addition, dibenzofuran (DF), ortho-hydroxydiphenyl and para-hydroxydiphenyl were identified as another group of photoproducts, indicating PBDEs can also undergo the photochemical rearrangement via CO bond cleavage and recombination of the radical fragments.

Anatomical regulation of ice nucleation and cavitation helps trees to survive freezing and drought stress

Water in the xylem, the water transport system of plants, is vulnerable to freezing and cavitation, i.e. to phase change from liquid to ice or gaseous phase. The former is a threat in cold and the latter in dry environmental conditions. Here we show that a small xylem conduit diameter, which has previously been shown to be associated with lower cavitation pressure thus making a plant more drought resistant, is also associated with a decrease in the temperature required for ice nucleation in the xylem. Thus the susceptibility of freezing and cavitation are linked together in the xylem of plants. We explain this linkage by the regulation of the sizes of the nuclei catalysing freezing and drought cavitation. Our results offer better understanding of the similarities of adaption of plants to cold and drought stress, and offer new insights into the ability of plants to adapt to the changing environment.

Removal and Degradation of Phenanthrene and Pyrene from Soil by Coupling Surfactant Washing with Photocatalysis

In this study, two environmental remediation technologies, surfactant washing and photocatalytic oxidation, have been investigated to remove and decompose phenanthrene (Phe) and pyrene (Pry). Aqueous solutions containing the anionic surfactant sodium dodecyl benzene sulfonate (SDBS) and the nonionic surfactant Tween-80 (TW-80) were used to extract the contaminants from the soil samples. The effects of concentration of surfactant, washing time and temperature on the desorption efficiency of the contaminants from soil samples were studied. The photocatalytic oxidation treatment of the obtained washing wastes, performed in the presence of Fenton-TiO2 suspensions irradiated with a 250W high pressure mercury lamp, showed an effective abatement of the two kinds of polycyclic aromatic hydrocarbons (PAHs) due to the relevant concentrations of organics in the waste. This study demonstrates the two-stage progress process can be an effective treatment method for PAHs not only desorption by soil washing but also degradation by photocatalytic oxidation.

Enhanced photodegradation of pentachlorophenol by single and mixed cationic and nonionic surfactants

The photocatalytic degradation of pentachlorophenol (PCP) using a TiO(2) catalyst in a surfactant-containing system was investigated. PCP abatement by photocatalysis was significantly enhanced by the addition of cationic and nonionic surfactants, both single and mixed, at appropriate concentrations. The enhanced photodegradation can be mainly attributed to the formation of admicelles on the TiO(2) surface. This phenomenon can lead to the incorporation of more PCP, thereby providing TiO(2) with remarkably higher capture rates for target pollutants. Hence, PCP was rendered easily available to photo-yielded oxidative radicals on the catalyst surface. Notably, mixed cationic-nonionic surfactants yielded much higher photodegradation efficiencies than the corresponding single surfactants, indicating the existence of a synergistic effect in the complex system. The adsorption behavior of PCP on TiO(2) in the surfactant solutions was investigated to elucidate this synergism. Fourier-transform infrared (FTIR) spectroscopy was adopted to gain insight into the structural changes induced by the surfactants and a better understanding of the surfactant-assisted photocatalytic degradation mechanism was obtained.

Cavitation induced by a surfactant leads to a transient release of water stress and subsequent 'run away' embolism in Scots pine (Pinus sylvestris) seedlings

Cavitation decreases the hydraulic conductance of the xylem and has, therefore, detrimental effects on plant water balance. However, cavitation is also hypothesized to relieve water stress temporarily by releasing water from embolizing conduits to the transpiration stream. Stomatal closure in response to decreasing water potentials in order to avoid excessive cavitation has been well documented in numerous previous studies. However, it has remained unclear whether the stomata sense cavitation events themselves or whether they act in response to a decrease in leaf water potential to a level at which cavitation is initiated. The effects of massive cavitation on leaf water potential, transpiration, and stomatal behaviour were studied by feeding a surfactant into the transpiration stream of Scots pine (Pinus sylvestris) seedlings. The stomatal response to cavitation in connection with the capacitive effect was also studied. A major transient increase in leaf water potential was found due to cavitation in the seedlings. As cavitation was induced by lowering the surface tension, the two mechanisms could be uncoupled, as the usual relation between xylem water potential and the onset of cavitation did not hold. Our results indicate that the seedlings responded more to leaf water potential and less to cavitation itself, as stomatal closure was insufficient to prevent the seedlings from being driven to 'run-away' cavitation in a manner of hours.

Adsorption of mixed cationic-nonionic surfactant and its effect on bentonite structure

The adsorption of cationic-nonionic mixed surfactant onto bentonite and its effect on bentonite structure were investigated. The objective was to improve the understanding of surfactant behavior on clay mineral for its possible use in remediation technologies of soil and groundwater contaminated by toxic organic compounds. The cationic surfactant used was hexadecylpyridinium bromide (HDPB), and the nonionic surfactant was Triton X-100 (TX100). Adsorption of TX100 was enhanced significantly by the addition of HDPB, but this enhancement decreased with an increase in the fraction of the cationic surfactant. Part of HDPB was replaced by TX100 which decreased the adsorption of HDPB. However, the total adsorbed amount of the mixed surfactant was still increased substantially, indicating the synergistic effect between the cationic and nonionic surfactants. The surfactant-modified bentonite was characterized by Brunauer-Emmett-Teller specific surface area measurement, Fourier transform infrared spectroscopy, and thermogravimetric-derivative thermogravimetric/differential thermal analyses. Surfactant intercalation was found to decrease the bentonite specific surface area, pore volume, and surface roughness and irregularities, as calculated by nitrogen adsorption-desorption isotherms. The co-adsorption of the cationic and nonionic surfactants increased the ordering conformation of the adsorbed surfactants on bentonite, but decreased the thermal stability of the organobentonite system.

Phytotoxicity of PFOS and PFOA to Brassica chinensis in different Chinese soils

PFOS and PFOA are potential persistent organic pollutants that have raised many concerns in recent years. Research focusing on phytotoxicity of PFOS and PFOA to higher plants is necessary for their risk assessments. However, few toxicity data exist for PFOS or PFOA and higher plants. Here we investigated phytotoxicity of PFOS and PFOA to Brassica chinensis root growth in six different Chinese soils varying widely in soil properties using a standardized root length assay. The effective concentrations of added PFOS and PFOA causing 50% inhibition (EC₅₀) ranged from 95 to > 200 mg kg⁻¹ for PFOS and from 107 to 246 mg kg⁻¹ for PFOA, respectively, representing more than 2.1- and 2.3-fold variation among the tested soils. Regressions of soil PFOS and PFOA toxicity threshold values (EC(x) and NOECs) with various soil properties showed that the amount of organic matter was the most significant factor affecting their toxicity to B. chinensis.

A column test for leaching of organochlorines from soil by amphiphilic nonionic nanopolymers

Amphiphilic nonionic cross-linked nanopolymers (NPs) were synthesized to examine removal of five organochlorines (OCs), namely lindane, heptachlor, aldrin, dieldrin, endrin, and DDT, from a range of Thai agricultural soils. The synthesized NP particles had polarity characteristics similar to those of nonionic surfactant micelles and were largely in the size range of 55-155 nm. This work aimed to determine the optimal conditions for leaching of OC contaminated soil with NPs and also to investigate the role and influence of soil properties on this leaching. An investigation of the concentrations of aqueous dispersions of these particles found that a concentration of 10 g L(-1). was found most effective in leaching the OCs from a column of spiked soil. The optimal contact time that allowed a NP dispersion and spiked soil to reach equilibrium was 48 h. The results indicated influencing factors for OC removal and soil remediation were properties both of the soil and the compounds themselves. Soil organic carbon (SOC) content and soil texture played an important role on the sorption as well as compound hydrophobicity expressed as log K(OW) values. The removal efficiency was found to be in the range of 85.2-92.8 % for all soil samples and in the order of DDT < aldrin < heptachlor < dieldrin < endrin < lindane regardless of soil type. This order is inversely related to the log K(OC) values of these compounds. For OC compounds with a similar molecular structure, removal efficiency was related to molecular weight (MW).

Surfactant-soil interactions during surfactant-amended remediation of contaminated soils by hydrophobic organic compounds: a review

Surfactants are amphiphilic molecules that reduce aqueous surface tension and increase the solubility of hydrophobic organic compounds (HOCs). Surfactant-amended remediation of HOC-contaminated soils and aquifers has received significant attention as an effective treatment strategy - similar in concept to using soaps and detergents as washing agents to remove grease from soiled fabrics. The proposed mechanisms involved in surfactant-amended remediation include: lowering of interfacial tension, surfactant solubilization of HOCs, and the phase transfer of HOC from soil-sorbed to pseudo-aqueous phase. However, as with any proposed chemical countermeasures, there is a concern regarding the fate of the added surfactant. This review summarizes the current state of knowledge regarding nonionic micelle-forming surfactant sorption onto soil, and serves as an introduction to research on that topic. Surfactant sorption onto soil appears to increase with increasing surfactant concentration until the onset of micellization. Sorbed-phase surfactant may account for the majority of added surfactant in surfactant-amended remediation applications, and this may result in increased HOC partitioning onto soil until HOC solubilization by micellar phase surfactant successfully competes with increased HOC sorption on surfactant-modified soil. This review provides discussion of equilibrium partitioning theory to account for the distribution of HOCs between soil, aqueous phase, sorbed surfactant, and micellar surfactant phases, as well as recently developed models for surfactant sorption onto soil. HOC partitioning is characterized by apparent soil-water distribution coefficients in the presence of surfactant.

Decontamination of soil washing wastewater using solar driven advanced oxidation processes

Decontamination of soil washing wastewater was performed using two different solar driven advanced oxidation processes (AOPs): the photo-Fenton reaction and the cobalt/peroxymonosulfate/ultraviolet (Co/PMS/UV) process. Complete sodium dodecyl sulphate (SDS), the surfactant agent used to enhance soil washing process, degradation was achieved when the Co/PMS/UV process was used. In the case of photo-Fenton reaction, almost complete SDS degradation was achieved after the use of almost four times the actual energy amount required by the Co/PMS/UV process. Initial reaction rate in the first 15min (IR15) was determined for each process in order to compare them. Highest IR15 value was determined for the Co/PMS/UV process (0.011mmol/min) followed by the photo-Fenton reaction (0.0072mmol/min) and the dark Co/PMS and Fenton processes (IR15=0.002mmol/min in both cases). Organic matter depletion in the wastewater, as the sum of surfactant and total petroleum hydrocarbons present (measured as chemical oxygen demand, COD), was also determined for both solar driven processes. It was found that, for the case of COD, the highest removal (69%) was achieved when photo-Fenton reaction was used whereas Co/PMS/UV process yielded a slightly lower removal (51%). In both cases, organic matter removal achieved was over 50%, which can be consider proper for the coupling of the tested AOPs with conventional wastewater treatment processes such as biodegradation.

Sustainable decontamination of an actual-site aged PCB-polluted soil through a biosurfactant-based washing followed by a photocatalytic treatment

A two phases process consisting of a soya lecithin (SL)-based soil washing process followed by the photocatalytic treatment of resulting effluents was developed and applied at the laboratory scale in the remediation of an actual-site soil historically contaminated by 0.65 g/kg of polychlorinated biphenyls (PCBs). Triton X-100 (TX) was employed in the same process as a control surfactant. SL and TX, both applied as 2.25 g/L aqueous solutions, displayed a comparable ability to remove PCBs from the soil. However, SL solution displayed a lower ecotoxicity, a lower ability to mobilize soil constituents and a higher soil detoxification capacity with respect to the TX one. The photocatalytic treatment resulted in marked depletions (from 50% to 70%) of total organic carbon (TOC) and PCBs initially occurring in the SL and TX contaminated effluents. Despite the ability of SL to adversely affect the rate of TOC and PCB photodegradation, higher PCB depletion and dechlorination yields along with lower increases of ecotoxicity were observed in SL-containing effluents with respect to the TX ones at the end of 15 days of treatment. The two phases process developed and tested for the first time in this study seems to have the required features to become, after a proper optimization and scale up, a challenging procedure for the sustainable remediation of actual site, poorly biotreatable PCB-contaminated soils.

Degradation of sodium dodecyl sulphate in water using solar driven Fenton-like advanced oxidation processes

Synthetic wastewater samples containing a model surfactant were treated using two different Fenton-like advanced oxidation processes promoted by solar radiation; the photo-Fenton reaction and Co/PMS/UV processes. Comparison between the different experimental conditions was performed by means of the overall surfactant degradation achieved and by obtaining the initial rate in the first 15 min of reaction (IR15). It was found that, for dark Fenton reaction, the maximum surfactant degradation achieved was 14% under low iron and oxidant concentration. Increasing Fenton reagents by one magnitude order, surfactant degradation achieved 63% in 60 min. The use of solar radiation improved the reaction rate by 17% under same conditions and an additional increase of 12.5% was obtained by adjusting initial pH to 2. IR15 values for dark and irradiated Fenton reactions were 0.143 and 0.154 mmol/min, respectively, for similar reaction conditions and this value increased to 0.189 mmol/min when initial pH was adjusted. The use of the Co/PMS system allow us to determine an increase in the degradation rate, for low reaction conditions (1 mM of transition metal; 4 mM oxidant) similar to those used in dark Fenton reaction. Surfactant degradation increased from 3%, for Fenton reaction, to 44.5% in the case of Co/PMS. When solar irradiation was included in the experiments, under same reaction conditions described earlier, surfactant degradation up to 64% was achieved. By increasing Co/PMS reagent concentration by almost 9 times under irradiated conditions, almost complete (>99%) surfactant degradation was reached in 5 min. Comparing IR15 values for Co/PMS and Co/PMS/UV, it allow us to observe that the use of solar radiation increased the degradation rate in one magnitude order when compared with dark experiments and further increase of reagent concentration increased reaction rate twice.

Removal and degradation of aromatic compounds from a highly polluted site by coupling soil washing with photocatalysis

The possible application of two environmental remediation technologies - soil washing and photocatalysis - to remove and decompose various aromatic pollutants present in excavated soils of a contaminated industrial site has been investigated. Aqueous solutions containing the non-ionic surfactant Brij 35 were used to extract the contaminants from the soil samples. The photocatalytic treatment of the obtained washing wastes, performed in the presence of TiO(2) suspensions irradiated with simulated sunlight, showed a slow abatement of the toxic compounds due to the relevant concentrations of organics in the waste. A neat improvement of the process performances, obtained by operating in the presence of added potassium peroxydisulfate, suggests a feasible treatment route.

Enhancement of ozone oxidation and its associated processes in the presence of surfactant: degradation of atrazine

In this study, the degradation of atrazine (ATZ) by ozone (O3) oxidation and its associated processes (i.e. UV, UV/O3) in the presence and absence of surfactant was investigated and compared. A non-ionic surfactant, Brij 35, was selected. It was found that the presence of a low concentration of surfactant could improve the removal of ATZ by increasing the dissolution of ozone and the indirect generation of hydroxyl radicals. The saturated ozone level and the reaction rate constants were increased with increasing the concentration of surfactant and then decreased at higher surfactant doses at pH level of 2.5. A similar trend was observed at pH level of 7.0 in the presence of bicarbonate ion, because it is capable of deactivating the hydroxyl radicals generating at higher pH level. However, when the radical reactions become dominant in the ozonation (at pH 7.0 without bicarbonate), the saturated ozone level was higher than that with bicarbonate and the kinetic rate constants were increased first and levelled off with increasing of the dose of surfactant. Through the examining of a proposed unit performance index, the low concentration of surfactant is surely beneficial to the ozonation process. Besides, the direct photolysis and photo-assisted ozonation were compared to the ozonation. A significant enhancement on the decay rate of ATZ was resulted exclusively by adding the surfactant. An enhancement index for quantifying the improvement of the various processes was developed.

Development and assessment of an innovative soil-washing process based on the use of cholic acid-derivatives as pollutant-mobilizing agents

Surfactant-aided soil washing is often proposed for the restoration of aged organic pollutant-contaminated soils. As many of commercial surfactants have been found to be toxic and recalcitrant, the opportunity to use in this process cheap, non-toxic, and biodegradable pollutant-mobilizing agents, such as deoxycholic acid (DA), bovine bile (BB), and the residue resulting from DA extraction from BB (BBR), was studied in this work. A soil historically contaminated by chlorinated anilines and benzenes, thiophenes, and several polycyclic aromatic hydrocarbons was suspended at 15% w/v and washed in water or water amended at 1.0% (w/v) with DA, BB, BBR, or Triton X-100 (TX). The resulting effluents were supplemented with nutrients and subjected to aerobic bioremediation. The biogenic agents enhanced the water pollutant elution potential by 230/440%. TX enhanced the same parameter by about 540%; however, it mediated a lower depletion of the initial soil ecotoxicity and a more extensive mobilization of soil constituents with respect to the biogenic agents. Furthermore, TX adversely affected the biotreatability of resulting effluents, by adversely affecting the growth of cultivable bacterial biomass and the structure of eubacterial community of the effluent. On the contrary, the biogenic agents, and in particular DA and BB, enhanced the effluents bioremediation, by sustaining the growth and increasing the complexity of the effluent eubacterial communities. Thus, DA and BB are very promising additives for an effective and environmental friendly soil washing treatment of aged (chloro)organics contaminated soils.

Effects of nonaqueous phase liquids on the washing of soil in the presence of nonionic surfactants

The removal of malathion from soil by surfactant washing was investigated under various physical-chemical states of the malathion. Three distinctive phases (without nonaqueous phase liquids (NAPL), with NAPL, and the transitional zone of NAPL) were found to be important for a better understanding of the washing process. When there is no NAPL in the system, the washing process is less dependent on the surfactant dose if the applied surfactant concentration is above the critical micelle concentration. The existence of a sorption site boundary, which for the determination of different washing mechanisms, was identified. In the presence of NAPL, the washing performance is generally independent of the organic content (f(oc)) of the soils but is dominated by the concentration of the surfactant used, due to the lesser resistance for mass transfer in NAPL. If the formation of NAPL is marginal, a two-stage washing pattern is observed, which has been quantified by the term 'unit extraction'. For this two-stage system, a mathematical model was derived based on the observed initial unit extraction and final extraction capacity, which eventually resulted in a practical design equation with the use of primary parameters such as f(oc) and surfactant dose.

Effects of cyclodextrins, humic substances, and rhamnolipids on the washing of a historically contaminated soil and on the aerobic bioremediation of the resulting effluents

Nontoxic and biodegradable pollutant-mobilizing agents, instead of chemical surfactants, were tested in the washing of an actual-site chloroaromatic-contaminated soil. A soil historically contaminated by chlorinated anilines and benzenes, thiophenes and several polycyclic aromatic hydrocarbons was subjected to washing by suspending it (15% w/v) in water or in water with 1.0% (w/v) beta-clodextrin (beta-CD), hydroxypropyl-beta-cyclodextrin (HP-beta-CD), rhamnolipid (RL), dissolved humic substances (HS), or Triton X-100 (TX) in shaken batch reactors for 24 hr. The resulting wastewaters were amended with nutrients and treated aerobically in shaken reactors for 65 days. The biogenic agents markedly enhanced (by 237%, beta-CD; 265%, HP-beta-CD; 400%, RL; 566%, HS) the capability of water of eluting organic pollutants from the soil. TX enhanced the overall pollutant removal by about 660%; however, a lower depletion of the initial soil ecotoxicity, along with a more extensive impact on the soil organic matter, was observed. Furthermore, TX adversely affected the bioremediation of the resulting effluent by apparently inducing a premature decrease of specialized bacterial biomass. By contrast, the biogenic agents, and in particular HS and RL, sustained the biodegradation and dechlorination of pollutants by apparently enhancing the availability of specialized bacteria in the reactors. Thus, the biogenic agents proposed here seem to be promising nontoxic and nonaggressive soil washing agents for the integrated physicochemical (washing) and biological (aerobic posttreatment) restoration of poorly bioremediable (chloro) organics-contaminated soils.

Distribution of phenanthrene between soil and an aqueous phase in the presence of anionic micelle-like amphiphilic polyurethane particles

Sorption of micelle-like amphiphilic polyurethane (APU) particles to soil was studied and compared to that of a model anionic surfactant, sodium dodecyl sulfate (SDS). Three types of APU particles with different hydrophobicity were synthesized from urethane acrylate anionomers (UAA) and used in this study. Due to the chemically cross-linked structure, APU exhibited less sorption to the soil than SDS and a greater reduction in the sorption of phenanthrene, a model soil contaminant, to the soil was observed in the presence of APU than SDS even though the solubility of phenanthrene was higher in the presence of SDS than APU. A mathematical model was developed to describe the phenanthrene distribution between soil and an aqueous phase containing APU particles. The sorption of phenanthrene to the test soil could be well described by Linear isotherm. APU sorption to the soil was successfully described by Langmuir and Freundlich isotherms. The partition of phenanthrene between water and APU were successfully explained with a single partition coefficient. The model, which accounts for the limited solubilization of phenanthrene in sorbed APU particles, successfully described the experimental data for the distribution of phenanthrene between the soil and the aqueous phase in the presence of APU.

Remediation of contaminated soil by a solvent/surfactant system

This study investigates a new approach using a solvent/surfactant-aided soil-washing process to improve the performance of conventional surfactant-aided soil remediation. Three surfactants (Brij 35, Tween 80, and SDS) and three organic solvents (acetone, triethylamine, and squalane) were used to evaluate the desorption performances of 4,4'-dichlorobiphenyl (DCB) out of three soils with different sorption characteristics. The performance improvement is likely due to better dissolution of the hydrophobic contaminants from the soil assisted by the solvent, and the formation of solvent-incorporated surfactant micelles, which increases both the size (i.e. capacity) and affinity of micelles for more effective contaminant extraction. The foc of soils were found to be important in determining the performance of a solvent/surfactant-aided soil-washing process. Judging from the experimental data and as verified by the two constants in the proposed soil-washing model, as the organic solvent is coexisting with the surfactant micelles, both the marginal soil-washing performance (right after the use of a very small amount of solvent compared to that of none) and the final soil-washing capacity are increased compared to those of a pure surfactant-aided washing process.

Effect of amphiphilic polyurethane nanoparticles on sorption-desorption of phenanthrene in aquifer material

Micelle-like amphiphilic nano-sized polyurethane (APU) nanoparticles were synthesized via chemical cross-linking reaction of nano-aggregates of urethane acrylate nonionomer (UAN) chain and were tested for extraction efficiency of sorbed phenanthrene from aquifer material. Even though the solubilizing performance and interfacial activity of APU nanoparticles were inferior to that of Triton X-100, in the low concentration region, APU nanoparticles could effectively reduce phenanthrene sorption on the aquifer material and extracted sorbed phenanthrene from the aquifer material, whereas Triton X-100 could not extract sorbed phenanthrene and rather increased phenanthrene sorption onto the aquifer materials. At higher concentrations, APU nanoparticles and Triton X-100 had almost the same soil washing effectiveness. This interesting result is mainly due to a lower degree of sorption of APU nanoparticles onto the aquifer material. The sorption of APU nanoparticles onto aquifer sand is largely hindered by their chemically cross-linked nature, resulting in better soil-washing performance of APU nanoparticles than Triton X-100.

Modeling the sequential photodechlorination of hexachlorobenzene in surfactant micelles

A five-stage consecutive irreversible model is derived to predict the photodegradation of hexachlorobenzene (HCB) in a surfactant solution, which was proven to be a useful treatment process following the surfactant-aided soil washing or remediation. The photodegradation of HCB in surfactant micelles is dominated by photodechlorination, which sequentially removes chlorides one at a time. The minor pathways of photoisomerization and photochlorination were neglected in the kinetic model. The results show that the derived consecutive irreversible model can accurately predict the decay of HCB and the formation (and decay) of its less-chlorinated congeners. The initial rate approach was used to identify the proper range of decay rate of each chlorinated benzene; so the overall rate constants can be determined easier by trial. The decreased performance of a completely mixed flow reactor (CMFR) with continuous input is also quantified compared to a batch reactor.