Emulsion-based recovery of a multicomponent petroleum hydrocarbon NAPL using nonionic surfactant formulations.

Surfactants can aid subsurface remediation through three primary mechanisms - solubilization, mobilization and/or emulsification. Among these mechanisms, emulsification in porous media is generally not well studied or well understood; particularly in the context of treating sources containing multicomponent NAPL. The objective of this research was to elucidate the processes responsible for recovery of a multicomponent hydrocarbon NAPL when surfactant solutions are introduced within a porous medium to promote the formation of kinetically-stable oil-in-water emulsions.

Chemotaxis Increases the Retention of Bacteria in Porous Media with Residual NAPL Entrapment.

Chemotaxis has the potential to decrease the persistence of nonaqueous phase liquid (NAPL) contaminants in aquifers by allowing pollutant-degrading bacteria to move toward sources of contamination and thus influence dissolution. This experimental study investigated the migratory response of chemotactic bacteria to a distribution of residual NAPL ganglia entrapped within a laboratory-scale sand column under continuous-flow at a superficial velocity of 0.05 cm/min.

Transport and Retention of Concentrated Oil-in-Water Emulsions in Porous Media.

Oil-in-water emulsions are routinely used in subsurface remediation. In these applications, high oil loadings present a challenge to remedial design as mechanistic insights into transport and retention of concentrated emulsions is limited. Column experiments were designed to examine emulsion transport and retention over a range of input concentrations (1.

Chemotaxis Increases the Residence Time of Bacteria in Granular Media Containing Distributed Contaminant Sources.

The use of chemotactic bacteria in bioremediation has the potential to increase access to, and the biotransformation of, contaminant mass within the subsurface. This laboratory-scale study aimed to understand and quantify the influence of chemotaxis on the residence times of pollutant-degrading bacteria within homogeneous treatment zones. Focus was placed on a continuous-flow sand-packed column in which a uniform distribution of naphthalene crystals created distributed sources of dissolved-phase contaminant.

Biodegradation and cometabolic modeling of selected beta blockers during ammonia oxidation.

Accurate prediction of pharmaceutical concentrations in wastewater effluents requires that the specific biochemical processes responsible for pharmaceutical biodegradation be elucidated and integrated within any modeling framework. The fate of three selected beta blockers-atenolol, metoprolol, and sotalol-was examined during nitrification using batch experiments to develop and evaluate a new cometabolic process-based (CPB) model. CPB model parameters describe biotransformation during and after ammonia oxidation for specific biomass populations and are designed to be integrated within the Activated Sludge Models framework.

Assessment of quantitative structural property relationships for prediction of pharmaceutical sorption during biological wastewater treatment.

In this study, we critically examined the available data related to pharmaceutical (PhAC) sorption in biological treatment processes. Using these data, we developed and assessed single and polyparameter quantitative structural activity models to better understand the role of sorption in PhAC attenuation. In contrast to other studies, our analysis suggests that values of the sorption coefficient (KD) are poorly correlated to single parameter models employing logKOW or the apparent partition coefficient (i.

Kinetic limitations on tracer partitioning in ganglia dominated source zones.

Quantification of the relationship between dense nonaqueous phase liquid (DNAPL) source strength, source longevity and spatial distribution is increasingly recognized as important for effective remedial design. Partitioning tracers are one tool that may permit interrogation of DNAPL architecture. Tracer data are commonly analyzed under the assumption of linear, equilibrium partitioning, although the appropriateness of these assumptions has not been fully explored.

Encapsulation of nZVI particles using a Gum Arabic stabilized oil-in-water emulsion.

Stabilization of reactive iron particles against aggregation and sedimentation is a critical engineering aspect for successful application of nZVI (nanoscale zero valent iron) within the contaminated subsurface environment. In this work we explore the stability and reactivity of a new encapsulation approach that relies upon Gum Arabic to stabilize high quantities of nZVI (∼ 12 g/L) in the dispersed phase of a soybean oil-in-water emulsion. The emulsion is kinetically stable due to substantial repulsive barriers to droplet-droplet induced deformation and subsequent coalescence.

Degradation product partitioning in source zones containing chlorinated ethene dense non-aqueous-phase liquid.

Abiotic and biotic reductive dechlorination with chlorinated ethene dense non-aqueous-phase liquid (DNAPL) source zones can lead to significant fluxes of complete and incomplete transformation products. Accurate assessment of in situ rates of transformation and the potential for product sequestration requires knowledge of the distribution of these products among the solid, aqueous, and organic liquid phases present within the source zone. Here we consider the fluid-fluid partitioning of two of the most common incomplete transformation products, cis-1,2-dichloroethene (cis-DCE) and vinyl chloride (VC).

Iron-mediated trichloroethene reduction within nonaqueous phase liquid.

Aqueous slurries or suspensions containing reactive iron nanoparticles are increasingly suggested as a potential means for remediating chlorinated solvent nonaqueous phase liquid (NAPL) source zones. Aqueous-based treatment approaches, however, may be limited by contaminant dissolution from the NAPL and the subsequent contaminant transport to the reactive nanoparticles. Reactions occurring within (or at the interface) of the NAPL may alleviate these potential limitations, but this approach has received scant attention due to concerns associated with the reactivity of iron within nonaqueous phases.

Predicting DNAPL mass discharge from pool-dominated source zones.

Models that link simplified descriptions of dense non-aqueous phase liquid (DNAPL) source zone architecture with predictions of mass flux can be effective screening tools for evaluation of source zone management strategies. Recent efforts have focused on the development and implementation of upscaled models to approximate the relationship between mass removal and flux-averaged, down-gradient contaminant concentration (or mass flux) reduction. The efficacy of these methods has been demonstrated for ganglia-dominated source zones.

Oil-in-water emulsions for encapsulated delivery of reactive iron particles.

Treatment of dense nonaqueous phase liquid (DNAPL) source zones using suspensions of reactive iron particles relies upon effective transport of the nano- to submicrometer scale iron particles within the subsurface. Recognition that poor subsurface transport of iron particles results from particle-particle and particle-soil interactions permits development of strategies which increase transport. In this work, experiments were conducted to assess a novel approach for encapsulated delivery of iron particles within porous media using oil-in-water emulsions.

Experimental and numerical validation of the total trapping number for prediction of DNAPL mobilization.

The total trapping number (N(T)), quantifying the balance of gravitational, viscous, and capillaryforces acting on an entrapped dense nonaqueous phase liquid (DNAPL) droplet was originally developed as a criterion to predict the onset and extent of residual DNAPL mobilization in porous media. The ability of this approach to predict mobilization behavior, however, has not been rigorously validated in multidimensional systems. In this work, experimental observations of residual tetrachloroethene (PCE) mobilization in rectangular columns are compared to predictions obtained using a multiphase compositional finite-element simulator that was modified to incorporate the dependence of entrapped residual,flow, and transport parameters on the total trapping number.

Evaluation of trichloroethene recovery processes in heterogeneous aquifer cells flushed with biodegradable surfactants.

The ability of two biodegradable surfactants, polyoxyethylene (20) sorbitan monooleate (Tween 80) and sodium dihexyl sulfosuccinate (Aerosol MA), to recover a representative dense non-aqueous-phase liquid (DNAPL), trichloroethene (TCE), from heterogeneous porous media was evaluated through a combination of batch and aquifer cell experiments. An aqueous solution containing 3.3% Aerosol MA, 8% 2-propanol and 6 g/l CaCl(2) yielded a weight solubilization ratio (WSR) of 1.

Pilot-scale demonstration of surfactant-enhanced PCE solubilization at the Bachman Road site. 2. System operation and evaluation.

A pilot-scale demonstration of surfactant-enhanced aquifer remediation (SEAR) was conducted during the summer of 2000 at the Bachman Road site in Oscoda, MI. Part two of this two-part paper describes results from partitioning and nonpartitioning tracer tests, SEAR operations, and post-treatment monitoring. For this field test, 68 400 L of an aqueous solution of 6% (wt) Tween 80 were injected to recover tetrachloroethene-nonaqueous phase liquid (PCE-DNAPL) from a shallow, unconfined aquifer.

Pilot-scale demonstration of surfactant-enhanced PCE solubilization at the Bachman Road site. 1. Site characterization and test design.

A pilot-scale demonstration of surfactant-enhanced aquifer remediation (SEAR) was conducted to recover dense nonaqueous phase liquid (DNAPL) tetrachloroethene (PCE) from a sandy glacial outwash aquifer underlying a former dry cleaning facility at the Bachman Road site in Oscoda, MI. Part one of this two-part paper describes site characterization efforts and a comprehensive approach to SEAR test design, effectively integrating laboratory and modeling studies. Aquifer coring and drive point sampling suggested the presence of PCE-DNAPL in a zone beneath an occupied building.

Coupling aggressive mass removal with microbial reductive dechlorination for remediation of DNAPL source zones: a review and assessment.

The infiltration of dense non-aqueous-phase liquids (DNAPLs) into the saturated subsurface typically produces a highly contaminated zone that serves as a long-term source of dissolved-phase groundwater contamination. Applications of aggressive physical-chemical technologies to such source zones may remove > 90% of the contaminant mass under favorable conditions. The remaining contaminant mass, however, can create a rebounding of aqueous-phase concentrations within the treated zone.

Stimulated microbial reductive dechlorination following surfactant treatment at the Bachman Road site.

A pilot-scale demonstration of surfactant-enhanced aquifer remediation (SEAR) was conducted in July 2000 at the Bachman Road site located in Oscoda, MI. The Bachman aquifer is a shallow, relatively homogeneous, unconfined aquifer formation composed primarily of sandy glacial outwash with relatively low organic carbon content (0.02 wt %).

Refinement of the density-modified displacement method for efficient treatment of tetrachloroethene source zones.

A novel method to remediate dense nonaqueous phase liquid (DNAPL) source zones that incorporates in situ density conversion of DNAPL via alcohol partitioning followed by displacement with a low interfacial tension (IFT) surfactant flood has been developed. Previous studies demonstrated the ability of the density-modified displacement (DMD) method to recover chlorobenzene (CB) and trichloroethene (TCE) from heterogeneous porous media without downward migration of the dissolved plume or free product. However, the extent of alcohol (n-butanol) partitioning required for in situ density conversion of high-density NAPLs, such as tetrachloroethene (PCE), could limit the utility of the DMD method.

Use of a surfactant-stabilized emulsion to deliver 1-butanol for density-modified displacement of trichloroethene.

A novel surfactant-enhanced aquifer remediation technology, density-modified displacement (DMD), has been developed to minimize risk of dense non-aqueous-phase liquid (DNAPL) downward migration during displacement floods. The DMD method is designed to be implemented using horizontal flushing schemes, with in situ DNAPL density conversion accomplished by the introduction of a partitioning alcohol (e.g.

Density-modified displacement for DNAPL source zone remediation: density conversion and recovery in heterogeneous aquifer cells.

Low interfacial tension (IFT) displacement (mobilization) of nonaqueous phase liquids (NAPLs) offers potential as an efficient remediation technology for contaminated aquifer source zones. However, displacement of dense NAPLs (DNAPLs) is problematic due to the tendency for downward migration and redistribution of the mobilized DNAPL. To overcome this limitation, a density-modified displacement method (DMD) was developed, which couples in situ density conversion of DNAPLs via alcohol partitioning with low IFT NAPL displacement and recovery.

Density-modified displacement for dense nonaqueous-phase liquid source-zone remediation: density conversion using a partitioning alcohol.

Entrapped and pooled dense nonaqueous-phase liquids (DNAPLs) often persist in aquifers and serve as a long-term source of groundwater contamination. To address the problematic nature of DNAPL remediation, a surfactant-enhanced aquifer remediation (SEAR) technology, density-modified displacement (DMD), has been developed which significantly reduces the risk of downward migration of displaced DNAPLs. The DMD method is designed to accomplish DNAPL density conversion through the introduction of a partitioning alcohol, n-butanol (BuOH), in a predisplacement flood using conventional horizontal flushing schemes.

Implications of alcohol partitioning behavior for in situ density modification of entrapped dense nonaqueous phase liquids.

Surfactant-based remediation techniques have the potential to be very effective for removing dense nonaqueous-phase liquids (DNAPLs) from contaminated sites. However, a risk associated with surfactant-based remediation of DNAPLs is the potential for unwanted downward mobilization of the DNAPL contaminants, making them more difficult to remove from the subsurface. The work described here examines the use of hydrophobic alcohol solutions to reduce the densities of entrapped DNAPLs, converting them to light nonaqueous-phase liquids (LNAPLs).