Numerical Investigation of the Impact of Ethanol on Flow in the Vadose Zone

Abstract

There is a need to elucidate the impact of ethanol on the subsurface environment because of the application of ethanol as automotive fuel. This study quantifies the effects of changes in surface tension, viscosity, and density induced by ethanol on the transmission and retention of water in the vadose zone. The HYDRUS-1D model was modified to simulate two different scenarios of flow in a sandy loam involving ponding (constant head) or spillage with a subsequent rainfall event (constant flux). Solutions containing different amounts of the highly miscible ethanol (10, 50, and 100% by weight) as well as pristine water were considered. During ponding, ethanol reduced the amount of fluid entering the soil and slowed down the advancement of the wetting front. Viscosity effects were predominant for this scenario, reducing the average depth of the infiltrating liquid up to 44%. The total amount of pure ethanol that entered the soil was 11.38 vs. 17.64 cm for pure water. For the spillage scenario, the results suggest that density has little impact on the liquid movement. Surface tension effects are predominant in the upper portion of the soil. The changes in hydraulic conductivity due to ethanol-induced modifications of solution viscosity are responsible for the slower advancement of the moisture front. The 10% ethanol solution moved 43.1% faster than pure ethanol during the first 2 d because of viscosity and surface tension effects.

Numerical Experiments for Surfactant Infiltration in the Vadose Zone to Demonstrate Concentration-Dependent Capillarity, Viscosity, and Sorption Characteristics

“…The scaling relationship for 7% w/w butanol solution is not directly applicable to pure ethanol because ethanol concentration-dependent impacts on density and kinematic [49,68] (surface tension and kinematic viscosity data are from [69]) (b) Dependence of surface tension, density and kinematic viscosity on ethanol concentration based on [53], surface tension data are from [70], density data from [71], viscosity data from [53].…”

“…Since the density of pure ethanol (0.789 g/cm 3 ) is significantly lower than that of pure water (0.998 g/cm 3 ) [71], the concentration-dependent density function becomes significant in the soil water pressure head scaling relationship. Therefore, in order to study the impacts of presence of ethanol on water retention, ethanol concentration-dependent functions of both surface tension and density should be considered [53]. In Equation (15), λ Ethanol represents the scaling factor for pure ethanol, ρ o represents the density at the reference concentration c o , and ρ(c) is the density at concentration c.…”

“…Sciortino and Leij (2012) [53] used Equation ( 16) to consider the changes in kinematic viscosity due to ethanol concentration.…”

“…By using the kinematic viscosity data from Sciortino and Leij (2012) [53], constants x, y, z, u, w are determined as 1.1681, 3.5749, 4.8091, 2.9825 and 1, respectively, (for relative concentrations of 1.0). Equation ( 16) is incorporated into Equation (12) to consider the pure ethanol effects on unsaturated hydraulic conductivity.…”

“…Additionally, ethanol with concentrations 70-95% are used in surfactant (co-solvent) flushing techniques [38]. Ethanol in high concentrations is used in both experimental (95%) [43] and numerical studies (100%) [53] in the literature. Triton X-100 is commonly investigated in numerical and experimental studies for its use for soil washing and agricultural purposes in a wide range of concentrations [54][55][56], some studies have used concentrations up to one hundred times of its CMC (15 g/L) [57].…”