Surfactant-enhanced Remediation Research Articles

Surfactant-enhanced remediation of contaminated soil: a review

Extracting aqueous solutions with or without additives are employed to solubilize contaminants in soil. Since water solubility is the controlling removing mechanism, additives are used to enhance efficiencies. These additives can reduce the time to treat a site compared to the use of water alone. Additives must be of low toxicity and biodegradable. The research in this area has focussed mainly on halogenated volatile organic compounds (VOCs) and is still quite limited for metal removal. Additives include surfactants, organic and inorganic acids, sodium hydroxide, which can dissolve organic soil matter, water-soluble solvents such as methanol, displacement of cations with nontoxic ones, complexing agents such as EDTA, acids in combination with complexing agents or oxidizing/reducing agents. Cationic, anionic and nonionic surfactants are particularly used for soil washing or flushing. They contain both hydrophobic and hydrophilic portions, making them ideal for solubilization of hydrophobic compounds. Numerous studies have indicated that surfactants enhance recoveries of non-aqueous phase liquids (NAPLs). There have also been indications that pretreatment of soil with surfactant washing to solubilize hydrophobic compounds such as PAHs enhances biodegradation of these contaminants. A few in situ field studies have been performed with surfactants. Large-scale treatment has been done mostly for organic removal. Soil pH, soil type, cation exchange capacity (CEC), particle size, permeabilities and contaminants all affect removal efficiencies. High clay and organic matter contents are particularly detrimental. Understanding the chemistry of the binding of the contaminant and the hydrogeology of the site are very important. Once the water is pumped from the soil, it must be extracted and then treated to remove the hydrocarbons and metals. Several technologies exist such as sodium hydroxide or sodium sulfide precipitation, ion exchange, activated carbon adsorption, ultrafiltration, reverse osmosis, electrodialysis and biological processes. Recycling of the surfactants is desired to decrease treatment costs. This paper will provide an overview of the laboratory research, field demonstration and full-scale application of surfactants for the remediation of contaminated soil. The majority of pilot scale in situ flushing tests, particularly in the United States, have involved the use of surfactants and co-solvents. There are only a few full-scale projects however. Recent laboratory scale efforts by the authors concerning the use of biosurfactants, biologically produced surfactants, to enhance the removal of copper, cadmium and zinc from contaminated soils and sediments are discussed. Three types of biosurfactants were evaluated for their effectiveness. They included a lipopeptide called surfactin from Bacillus subtilis, a rhamnolipid from Pseudomonas aeruginosa and a sophorolipid from Torulopsis bombicola. The results indicated the feasibility of removing the metals with the anionic biosurfactants even though the exchangeable fractions were not significant.

Environmental Modeling-A Project Driven, Team Approach to Theory and Application

Environmental modeling is an important tool for understanding and managing complex environmental systems. Regardless of discipline, complete modeling includes a number of steps, ranging from conceptualization to application. However, modeling courses often focus on just one, or at most a few, of the steps and frequently are assignment-driven. Moreover, they often present numerical procedures as recipes, without regard to theory or limitations and without regard to “real-world” application. In this course, we unify the modeling sequence by exposing students to the full spectrum of modeling (mathematics, physics, and numerical methods) in the context of surfactant-enhanced remediation of contaminated soils, a technology being developed at the University of Oklahoma. An innovative course structure is used that couples team learning with a project-driven syllabus (also referred to as just-in-time learning) and combines mathematical and physical modeling via data from laboratory and field testing. Other thematic areas can easily be developed in the same framework. We believe the course pedagogy is highly portable and can serve as an example for any modeling course or for many other courses in an engineering curriculum.

The influence of field-scale heterogeneity on the surfactant-enhanced remediation of entrapped nonaqueous phase liquids

Numerical simulation techniques are used to explore the surfactant-enhanced solubilization of a spill of tetrachloroethylene (PCE) entrapped in a heterogeneous, saturated sandy aquifer. A two-dimensional, multicomponent solubilization simulator is employed to simulate spill cleanup, utilizing ensembles of realizations of random, spatially correlated permeability fields. Flushing volumes required to remove the organic liquid and to reduce effluent concentrations to specified levels are used as measures of remediation effectiveness. Simulations illustrate the long-term persistence of nonaqueous phase liquid (NAPL) in low permeability regions and associated tailing of effluent organic concentrations. The tendency of the high concentration organic plumes to migrate downward under gravity forces is also demonstrated, and is shown to enhance migration of aqueous phase organic into regions of low permeability, causing substantially increased concentration tailing. Remediation efficiency is shown to be strongly dependent on spatial correlation structure and variance of the permeability distribution. Delivery of surfactant to low permeability regions is primarily controlled by transverse mixing processes. The influence of local mass transfer limitations on cleanup efficiency, although statistically significant, is found to be relatively minor for the contamination scenarios explored.

Competitive Substrate Biodegradation during Surfactant-Enhanced Remediation

The impact of synthetic surfactants on the aqueous phase biodegradation of benzene, toluene, and p-xylene (BTpX) was studied using two anionic surfactants, sodium dodecyl sulfate (SDS) and sodium dodecyl benzene sulfonate (SDBS), and two nonionic surfactants, POE(20) sorbitan monooleate (T-maz-80) and octylphenolpoly(ethyleneoxy) ethanol (CA-620). Batch biodegradation experiments were performed to evaluate surfactant biodegradability using two different microbial cultures. Of the four surfactants used in this study, SDS and T-maz-80 were readily degraded by a microbial consortium obtained from an activated sludge treatment system, whereas only SDS was degraded by a microbial culture that was acclimated to BTpX. Biodegradation kinetic parameters associated with SDS and T-maz-80 degradation by the activated sludge consortium were estimated using respirometric data in conjunction with a nonlinear parameter estimation technique as μmax = 0.93 h−1, Ks = 96.18 mg/L and μmax = 0.41 h−1, Ks = 31.92 mg/L, respectively. When both BTpX and surfactant were present in the reactor along with BTpX-acclimated microorganisms, two distinct biodegradation patterns were seen. SDS was preferentially utilized inhibiting hydrocarbon biodegradation, whereas the other three surfactants had no impact on BTpX biodegradation. None of the four surfactants were toxic to the microbial cultures used in this study. Readily biodegradable surfactants are not very effective for subsurface remediation applications as they are rapidly consumed, and also because of their potential inhibitory effects on intrinsic hydrocarbon biodegradation. This greatly increases treatment costs as surfactant recovery and reuse are adversely affected.

Partitioning of Hydrophobic Organic Compounds to Hydroxypropyl-β-cyclodextrin: Experimental Studies and Model Predictions for Surfactant-Enhanced Remediation Applications

Partitioning studies of hydrophobic organic compounds (HOCs) to hydroxypropyl-β-cyclodextrin (HPCD) and one-dimensional transport simulations were conducted to evaluate the feasibility of using HPCD to remove sorbed HOCs in surfactant-enhanced remediation (SER) applications. HOC partitioning to HPCD was very fast, with over 95% of the complexation occurring within 10 min. Some influence of solution chemistry and HOC concentration on HOC−HPCD complex formation coefficients was observed; in general, the magnitude of the effects was similar to that observed previously for a nonionic surfactant (Tween 80) but much less than that for an anionic surfactant (sodium dodecyl sulfate, SDS). HPCD sorption on kaolinite as quantified by both a fluorescence technique and total organic carbon measurements was negligible, indicating no significant affinity of HPCD for the solid phase. Although the HOC solubilization capability of HPCD was lower than that of conventional surfactants such as SDS and Tween 80, transport sim...

Partitioning of Hydrophobic Organic Compounds to Sorbed Surfactants. 2. Model Development/Predictions for Surfactant-Enhanced Remediation Applications

A one-dimensional numerical model was developed to simulate the performance of surfactant-enhanced remediation (SER) applications for saturated subsurface systems containing adsorbed hydrophobic organic compounds (HOCs). The model incorporates temporally and spatially dependent HOC and surfactant mass balance equations to compute distributions in the aqueous, micellar, sorbed surfactant, and subsurface solid phases. In particular, the model accounts for losses of surfactant by sorption to the subsurface media and for the subsequent partitioning of HOCs to sorbed surfactant. Parameter values for the model were estimated from experimental rate and equilibrium data from the literature, and sensitivity analysis was conducted to evaluate the model performance and potential SER applications. Simulation results show that the relative affinity of HOCs and surfactants for the immobile subsurface solid phase (i.e., the respective retardation factors) is critical for determining whether contaminant desorption can be...

Partitioning of Hydrophobic Organic Compounds to Sorbed Surfactants. 1. Experimental Studies

Partitioning of two hydrophobic organic compounds (HOCs), phenanthrene and naphthalene, to surfactant micelles, kaolinite, and sorbed surfactants was studied to provide further insight on (1) the effectiveness of using sorbed surfactants to remove HOCs from water and (2) the feasibility of surfactant-enhanced remediation (SER) for contaminated subsurface systems. Sorbed surfactant partition coefficients, Kss, showed a strong dependence on the surfactant sorption isotherms: at low sorbed surfactant levels Kss values were at their highest and then decreased with increasing surfactant sorption densities. Kss values for SDS were always larger than the corresponding micellar partition coefficient (Kmic) values; for Tween 80, however, Kss values were higher than Kmic values only at the lower sorbed surfactant densities. HOC distributions between the immobile and mobile phases varied with surfactant dose because of the competition between sorbed and micellar surfactants for HOC partitioning: distribution coeff...

Surfactant-Enhanced Remediation of a Trichloroethene-Contaminated Aquifer. 2. Transport of TCE

Field studies were conducted under an induced gradient in a trichloroethene (TCE)-contaminated aquifer at Picatinny Arsenal, NJ, to study (a) the rate-limited desorption of TCE from aquifer sediments to water and (b) the effect of a surfactant (Triton X-100) on the desorption and transport of TCE. Clean water was injected into the contaminated aquifer for 206 day. Triton X-100 was added for a 36-day period (days 36−71 from the start of clean water injection). The effect of Triton X-100 on the desorption and transport of TCE in the field was examined by observing the concentrations of these two solutes in four monitoring wells 3−9 m from the injection wells. These data show a small but discernible increase in the TCE concentration in two of the wells corresponding approximately to the time when surfactant reaches the wells; in the other two monitoring wells, the increase in TCE concentration is negligible. A solute transport model that assumes local sorption equilibrium and used a laboratory-derived distribution coefficient could not adequately describe TCE desorption and transport observed in the aquifer. Two model formulations that accounted for rate-limited sorptiontwo-site and multisite modelsfit the data well. TCE concentrations after surfactant injection were underpredicted by the models unless mass transfer rate was increased to account for the effect of surfactant on the rate of TCE desorption. The concentration data from the two wells and the model analysis suggest that the rate of TCE desorption is increased (by approximately 30%) as a result of Triton X-100 injection.

Surfactant-Enhanced Remediation of a Trichloroethene-Contaminated Aquifer. 1. Transport of Triton X-100

Transport of a nonionic surfactant (Triton X-100) at aqueous concentrations less than 400 mg/L through a trichloroethene-contaminated sand-and-gravel aquifer at Picatinny Arsenal, NJ, has been studied through a series of laboratory and field experiments. In the laboratory, batch and column experiments were conducted to quantify the rate and amount of Triton X-100 sorption to the aquifer sediments. In the field, a 400 mg/L aqueous Triton X-100 solution was injected into the aquifer at a rate of 26.5 L/min for a 35-d period. The transport of Triton X-100 was monitored by sampling and analysis of groundwater at six locations surrounding the injection well. Equilibrium batch sorption experiments showed that Triton X-100 sorbs strongly and nonlinearly to the field soil with the sharpest inflection point of the isotherm occurring at an equilibrium aqueous Triton X-100 concentration close to critical micelle concentration. Batch, soil column, and field experimental data were analyzed with zero-, one-, and two-di...

Surfactant-Enhanced Remediation of Saturated Ottawa Sand Contaminated by Ethylbenzene : ABSTRACT

Surfactant-Enhanced Remediation of Saturated Ottawa Sand Contaminated by Ethylbenzene : ABSTRACT