Jeffrey H. Harwell

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

Precipitation phenomena in mixtures of anionic and cationic surfactants in aqueous solutions

Abstract The precipitation phase boundary for mixtures of sodium dodecyl sulfate (NaDS) and dodecylpyridinium chloride (DPCl) is determined over a wide range of concentrations. The phase boundary is composed of a monomer—precipitate equilibrium curve, where no micelles exist in solution, and two branches (one NaDS-rich and one DPCl-rich) where monomer, micelles, and precipitate exist in equilibrium. A model is developed to predict the precipitation boundary by combining regular solution theory, to calculate monomer—micelle equilibrium, with a solubility product relationship between surfactant monomer concentrations, to calculate monomer—precipitate equilibrium. Results from the model are shown to work well, except in regions where coacervate formation occurs. An empirical modification to the model is used to account for coacervate formation so that all experimental phase boundaries can be described quite well. The model can also predict the amount of precipitate that will form in any NaDS—DPCl mixture and the results are shown to agree well with experimental measurements.

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.

Precipitation of mixtures of anionic and cationic surfactants: II. Effect of surfactant structure, temperature, and pH

Abstract Precipitation phase boundaries for sodium alkyl sulfate/dodecylpyridium chloride were measured over a wide range of surfactant concentrations as a function of pH, temperature, and anionic surfactant alkyl chain length. Increasing temperature and decreasing surfactant alkyl chain length generally tend to decrease the tendency to precipitate. A previously developed model for predicting anionic/cationic surfactant precipitation phase boundaries described the experimental results very well except in some high surfactant concentration regions where coacervate and gels formed. This model uses a simple solubility product relationship, with regular solution theory, to describe mixed micelle formation. The environment of the alkyl chains is more favorable in the precipitate than in the micelles, from measured thermodynamic properties.

Surfactant Recovery from Water Using Foam Fractionation

The purpose of this study was to investigate the use of foam fractionation to recover surfactant from water. A simple continuous mode foam fractionation was used and three surfactants were studied (two anionic and one cationic). The effects of air flow rate, foam height, liquid height, liquid feed surfactant concentration, and sparger porosity were studied. This technique was shown to be effective in either surfactant recovery or the reduction of surfactant concentration in water to acceptable levels. As an example of the effectiveness of this technique, the cetylpyridinium chloride concentration in water can be reduced by 90% in one stage with a liquid residence time of 375 minutes. The surfactant concentration in the collapsed foam is 21.5 times the feed concentration. This cationic surfactant was easier to remove from water by foam fractionation than the anionic surfactants studied.