Modeling benzene plume elongation mechanisms exerted by ethanol using RT3D with a general substrate interaction module

Abstract

[1] A mathematical model was developed to evaluate the effect of the common fuel additive ethanol on benzene fate and transport in fuel-contaminated groundwater and to discern the most influential benzene plume elongation mechanisms. The model, developed as a module for the Reactive Transport in 3 Dimensions (RT3D) model, includes commonly considered fate and transport processes (advection, dispersion, adsorption, biodegradation, and depletion of molecular oxygen during biodegradation) and substrate interactions previously not considered (e.g., a decrease in the specific benzene utilization rate due to metabolic flux dilution and/or catabolite repression) as well as microbial population shifts. Benzene plume elongation predictions, based on literature model parameters, were on the order of 40% for a constant source of E10 gasoline (10% vol/vol ethanol), which compares favorably to field observations. For low benzene concentrations (<1 mg/L), oxygen depletion during ethanol degradation was the principal mechanism hindering benzene natural attenuation. For higher benzene concentrations (exerting an oxygen demand higher than the available dissolved oxygen), metabolic flux dilution was the dominant plume elongation process. If oxygen were not limiting, as might be the case in zones undergoing aerobic biostimulation, model simulations showed that microbial growth on ethanol could offset negative substrate interactions and enhance benzene degradation, resulting in shorter plumes than baseline conditions without ethanol.Citation: Gomez, D. E., P. C. de Blanc, W. G. Rixey, P. B. Bedient, and P. J. J. Alvarez (2008), Modeling benzene plume elongation mechanisms exerted by ethanol using RT3D with a general substrate interaction module, Water Resour. Res., 44, W05405,

Analytical model for BTEX natural attenuation in the presence of fuel ethanol and its anaerobic metabolite acetate

“…Therefore the presence of ethanol and ethanol-derived acetate in groundwater can contribute to longer BTEX plumes (Ruiz-Aguilar et al, 2002;Corseuil et al, 2011) increasing the risk of human exposure ). These observations have been corroborated by laboratory studies (Corseuil et al, 1998;Da Silva and Alvarez, 2002;Cápiro et al, 2007Cápiro et al, , 2008, field research (Ruiz-Aguilar et al, 2002;Corseuil et al, 2011) and modeling studies (Heermann and Powers, 1998;Mcnab et al, 1999;Molson et al, 2002;Gomez et al, 2008;Alvarez, 2009, 2010). Nevertheless, the intensity of these effects can be system specific, which underscores the need for simple models that facilitate preliminary risk assessment and evaluate the potential performance of natural attenuation.…”

Inhibitory effect of natural organic matter or other background constituents on photocatalytic advanced oxidation processes: Mechanistic model development and validation

“…variable (Gomez et al 2008). A point elasticity value of 1 for a given parameter indicates that a 10% 290 change in that parameter will result in a 10% change in the modeled degradation rate.…”

Biodegradation of Soybean and Castor Oil Biodiesel: Implications on the Natural Attenuation of Monoaromatic Hydrocarbons in Groundwater

“…similar mechanisms as those reported for the common fuel additive, ethanol. When dissolved at concentrations greater than about 10,000 mg/L, ethanol can exert cosolvency, which could result in faster hydrocarbon dissolution from the oily phase and faster migration (i.e., decreased sorption-related retardation) in the aquifer (Groves 1988;Corseuil et al 2004;Cápiro et al 2007;Gomez et al 2008), thereby contributing to hydrocarbon plume elongation. However, the viscosity, solubility, and resulting migration properties of these two biofuels are significantly different, which would likely impact hydrocarbon natural attenuation and plume dynamics in different ways.…”