Surfactant-Enhanced Dissolution of Phenanthrene into Water for Laminar Flow Conditions

Abstract

The effects of surfactant solutions on processes influencing subsurface remediation are of significant environmental concern. We previously investigated the dissolution of solid phenanthrene into aqueous solutions containing nonionic surfactants in a wellmixed system and developed a mechanistic model to describe the dissolution process. In the present work, we challenged this model by collecting data from a flow-through system in which the hydrodynamics are well defined and provided independent measurements of all parameters in the model. The dissolution process is assumed to be governed by the diffusion of phenanthrene away from the hydrocarbon-water interface in both the aqueous phase and micelles, and transport is formulated in a threedimensional advective-diffusive model. The trends in model predictions and experimental data compare favorably, lending further support to the proposed mechanistic model. In particular, effluent concentrations of phenanthrene from the experimental apparatus were both predicted and observed to be substantially lower than saturation (equilibrium) concentrations, and this difference increased at increasing surfactant concentration over the range of laminar flow rates tested. Better quantitative agreement between the model and experimental data may require a more accurate measurement of the micellar diffusion coefficient or a more complex description of interfacial processes. However, the proposed dissolution model provides an important step toward understanding the influence of surfactants on hydrocarbon dissolution and transport.

Kinetic model of biosurfactant-enhanced hexadecane biodegradation byPseudomonas aeruginosa

“…The model parameter k s is a lumped kinetic parameter that represents the surfactant solubilization of HOC and subsequent transport of micellar phase HOC to the cell. Previous models and studies have also discussed the potential for surfactant micelle formation on the surface of the NAPL droplet with subsequent diffusion of the HOC containing micelle through the hydrodynamic boundary layer for being the rate-limiting process in insoluble hydrocarbon dissolution (Grimberg et al, 1995(Grimberg et al, , 1996. Subsequent diffusion of the HOC-containing micelle through the bulk aqueous phase and contact with the microorganisms are also required for HOC biodegradation.…”

“…Mechanistic models have been recently developed that describe the influence of nonionic surfactants on the rate of solid-phase HOC dissolution under laminar flow conditions which may be useful in prediction of surfactant-enhanced transport and HOC dissolution in solid/aqueous-phase environments (Grimberg et al, 1995(Grimberg et al, , 1996. We have developed a mechanistic model that describes the influence of biological surfactants on microbial biodegradation of liquid phase insoluble hydrocarbon and subsequent dissolution of nonaqueous-phase liquid (NAPL) HOC.…”

Modelling the fate of oxidisable organic contaminants in groundwater

“…(56) and (b) the two-step transformation involving acetate and its subsequent degradation, Eqs. (57) and (58). Thus, for this latter case, carbon (from molasses) is diverted between HCO − 3 (or other inorganic CO 2 species), acetate and microbial mass (with an estimated efficiency of 20%).…”

“…(11) and (12) are standard forms, applicable to dilute aqueous phases. For non-dilute aqueous phases, such as those with a chemical or biological surfactant, alternative models accounting for micelle formation and interchange across the NAPL-aqueous phase interface are more appropriate [58]. Surfactant systems are slower to achieve equilibrium than non-surfactant systems [59].…”

“…NAPL dissolution is an extremely complex process because (a) many NAPLs are complex mixtures, which complicates the equilibrium model needed; (b) the common rate model used, while simple in basic form, has a coefficient that depends upon many additional parameters and space and time; (c) mass transfer occurs across the interfacial area between the two phases of concern, which is not an accessible quantity in standard multiphase models; and (d) NAPL-aqueous phase mass transfer is an inherently unstable process, giving rise to the formation of complex dissolution fingering patterns in most natural systems [47,54,58,60,61].…”