David A. Sabatini

Coupled Iron Corrosion and Chromate Reduction: Mechanisms for Subsurface Remediation

The reduction of chromium from the Cr(VI) to the Cr(III) state by the presence of elemental, or zero-oxidation-state, iron metal was studied to evaluate the feasibility of such a process for subsurface chromate remediation. Reactions were studied in systems of natural aquifer materials with varying geochemistry. Different forms of iron metal had significantly different abilities to reduce chromate, ranging from extremely rapid to essentially no effect. Impure, partially oxidized iron was most effective, with iron quantity being the most important rate factor, followed by aquifer material type and solid :solution ratio. Evidence for chromium-iron hydroxide solid solution (Cr x, Fe 1-x )(OH) 3 (ss) formation was obtained by electron probe microanalysis. A cyclic, multiple reaction electrochemical corrosion mechanism, enhanced by the development of an electrical double-layer analogue, is proposed to explain the differing iron reactivities and aquifer material effects.

Surfactant selection for enhancing ex situ soil washing

Ex situ soil washing is commonly used for treating contaminated soils by separating the most contaminated fraction of the soil for disposal. Surfactant-enhanced soil washing is being considered with increasing frequency to actually achieve soil-contaminant separation. In this research eight anionic and nonionic surfactants were evaluated for the enhanced soil washing of three different soils contaminated with petroleum hydrocarbons. Enhanced soil washing occurred at surfactant concentrations below and above the CMC indicating the occurrence of both soil rollup and solubilization mechanisms. In certain cases the lower CMC of nonionic surfactants made them attractive candidates while in other cases the lower sorption and higher solubilization potential of select anionic surfactants made them the preferred choice. Surfactant-induced foaming and turbidity are operating considerations that can also impact surfactant selection. When selecting a surfactant for a given soil-contaminants system we thus recommend evaluating both anionic and nonionic surfactants at concentrations below and above their CMC, and we suggest that the methodology we describe in this paper is a good approach for making the final surfactant selection.

Influence of surfactants on microbial degradation of organic compounds

Abstract Surfactants have the ability to increase aqueous concentrations of poorly soluble compounds and interfacial areas between immiscible fluids, thus potentially improving the accessibility of these substrates to microorganisms. However, both enhancements and inhibitions of biodegradation of organic compounds in the presence of surfactants have been reported. The mechanisms behind these phenomena are not well understood. To better understand the factors involved and the current state of knowledge in this field, a search of the literature concerning the influence of commercial surfactants and biosurfactants on microbial metabolism has been conducted. Factors pertaining to surfactant‐substrate interactions such as emulsification, solubilization, and partitioning of hydrocarbons between phases, all of which can influence accessibility of substrates to microorganisms, are of concern. Also, due to the direct interaction of surfactants with microorganisms, it appears that steric or conformational compatibi...

Surfactants for ground water remediation

Ground water contamination is a most intractable form of pollution. Spilled solvent or fuel liquids are trapped below the water table by colloidal forces. Surfactants may be used to dramatically improve contaminated aquifer remediation rates. Principal remediation mechanisms include micellar solubilization and mobilization of the trapped liquids by lowering of the oil/water interfacial tension. Surfactant selection is a key to the successful design of a remediation effort, and involves consideration of factors including Krafft Point, surfactant adsorption onto the aquifer solids, and the phase behavior of the oil/water/surfactant system. Successful field demonstrations have occurred in recent months and the technology is moving rapidly toward commercialization. Critical research issues remain including acceptable clean-up levels, surfactant/contaminant in situ biodegradation rates, and surfactant decontamination and reuse.

Surfactant adsolubilization and modified admicellar sorption of nonpolar, polar, and ionizable organic contaminants

Adsolubilization of contaminants by media-sorbed surfactants is an important phenomenon for surfactant-based environmental technologies. The present research evaluates the impacts of contaminant properties on adsolubilization (e.g., nonpolar, polar, and ionizable organic compounds). In addition, adsolubilization by modified admicelles is investigated (operating below the surfactants Krafft temperature). The medium and surfactant investigated were alumina and sodium dodecyl sulfate, respectively. Naphthalene, naphthol, and 4-amino-1-naphthalenesulfonic acid were investigated as nonpolar, polar, and ionizable organic compounds, respectively. Variations in adsolubilization results for these compounds are explained based on surfactant fundamentals and contaminant properties

Integrated design of surfactant enhanced DNAPL remediation : Efficient supersolubilization and gradient systems

Abstract Widespread use of petroleum hydrocarbons and chlorinated solvents has resulted in contamination of soils and ground water supplies. This paper summarizes key technical and economic issues for surf ace act ive a ge nt (surfactant)-enhanced remediation of such contamination episodes. Laboratory and field results are cited illustrating each of these key issues. Using the design of an upcoming field study as an example, we illustrate the importance of system solubility enhancement, interfacial tension, viscosity and density in selecting a surfactant system. We also show how a site-specific capillary curve can be used to optimize contaminant solubility (super solubilization) while mitigating mobilization and vertical migration. Finally, we demonstrate the potential of a surfactant gradient system to progressively increase the super-solubilization potential without mobilizing trapped oil.

Hydrophilic-lipophilic deviation (HLD) method for characterizing conventional and extended surfactants

An accurate determination of the hydrophilic-lipophilic nature of surfactants plays an essential role in guiding the formulation of microemulsion with the goal of achieving low interfacial tension (IFT) and high solubilization. While several empirical models have been proposed as simple tools for predicting surfactant characteristics and microemulsion conditions, only a few of these models are fundamentally based yet convenient to use. In this work, the hydrophilic-lipophilic deviation (HLD) approach was used with mixed surfactant systems to determine the surfactant characteristic (sigma) and the sigmaK parameter of conventional and extended surfactants. To our knowledge, this is the first time that the HLD index has been used to represent the hydrophilic-lipophilic behavior of extended surfactants. It was observed that inserting PO and/or EO groups in extended surfactants play a key role in altering sigma values and sigmaK values. Finally, the sigma parameters found in this work were combined with the HLD equation and used to demonstrate its practical utility for guiding the optimum formulation (in this case, optimum salinity) for a microemulsion system.

Properties of food grade (edible) surfactants affecting subsurface remediation of chlorinated solvents.

In this research, several food grade (edible) surfactants are systematically evaluated for various loss mechanisms : precipitation, adsorption, and coacervation (for nonionic surfactants). Cloud points for the polyethoxylate sorbitan (T-MAZ) surfactants are much higher than aquifer temperatures, and the effects on surfactant losses should be minimum. Precipitation boundaries of bis(2-ethylhexyl) sodium sulfosuccinate (AOT) and sodium mono- and dimethylnaphthalene sulfonate (SMDNS) were established. Existing precipitation models successfully predicted precipitation boundaries for SMDNS but showed minor deviations for AOT results. AOT was more susceptible to precipitation than the cosurfactant evaluated, SMDNS. Nonionic polyethoxylate (POE = 20) sorbitan monostearate (T-MAZ-60) and POE(80) sorbitan monolaurate (T-MAZ-28) formed liquid crystal phases at high surfactant concentrations (>0.5 wt %) while POE(20) sorbitan monolaurate (T-MAZ-20) and POE(20) sorbitan monooleate (T-MAZ-80) remained in aqueous solution at concentrations up to 5 wt %. T-MAZ-60 and T-MAZ-28 also showed a continuous increase of adsorption at high surfactant concentrations (likely due to liquid crystal formation). Other surfactants showed Langmuirian-shaped isotherms at high concentration, while the cosurfactant SMDNS experienced negligible adsorption. On a mass basis, the maximum adsorption (q max in μmol/g) was higher for T-MAZ surfactants than for alkylphenol ethoxylates, AOT, and disulfonated surfactants.

Linker molecules in surfactant mixtures

Abstract Linker molecules are amphiphiles that segregate near the microemulsion membrane either near the surfactant tail (lipophilic linkers) or the surfactant head group (hydrophilic linkers). The idea of the lipophilic linkers was introduced a decade ago as a way to increase the surfactant–oil interaction and the oil solubilization capacity. Long chain (>9 tail carbons) alcohols were first used as lipophilic linkers. Later it was found that the solubilization enhancement plateaus (saturates) above a certain lipophilic linker concentration. Hydrophilic linkers have been recently introduced as a way to compensate for the saturation effect observed for lipophilic linkers. Hydrophilic linkers are surfactant-like molecules with 6–9 tail carbons that coadsorb with the surfactant at the oil/water interface, thereby increasing the surfactant–water interaction, but have a poor interaction with the oil phase due to their short tail. A special synergism emerges when combining hydrophilic and lipophilic linkers, which further increases the solubilization enhancement over lipophilic linkers alone. We will discuss the profound impact of linker molecules on interfacial properties such as characteristic length, interfacial rigidity and dynamics (coalescence, solubilization and relaxation experiments) of the interface. We also demonstrate how these properties affect the performance of cleaning formulations designed around linker molecules. We describe linker-based formulations for a wide range of oils, including highly hydrophobic oils (e.g. hexadecane) that have proven very hard to clean. We also report on the use of ‘extended’ surfactants as an alternative to self-assembled linker systems.

Separation of Organic Compounds from Surfactant Solutions: A Review

Abstract This review summarizes the recent development in separation of emulsified organic compounds from surfactant solutions for surfactant reuse and/or surfactant‐contaminant disposal. Three major principles have been employed for separating organic compounds and/or surfactants from aqueous solutions, namely, organic compound inter‐phase mass transfer, surfactant micelle removal, and manipulation of surfactant solution phase behavior. Details of these principles and their applications are discussed, with the advantages and limitations of each separation method compared. Separation based on mass transfer of the organic compounds into a secondary phase is currently more practical than the others. Finally, two major issues requiring further research are identified.