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Effect of colloids on volatile contaminant transport and air‐water partitioning in unsaturated porous media
Author(s) -
Choi Heecheul,
Corapcioglu M. Yavuz
Publication year - 1997
Publication title -
water resources research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.863
H-Index - 217
eISSN - 1944-7973
pISSN - 0043-1397
DOI - 10.1029/97wr02229
Subject(s) - mass transfer , colloid , porous medium , aqueous two phase system , chemistry , phase (matter) , aqueous solution , dimensionless quantity , chemical engineering , porosity , chromatography , thermodynamics , organic chemistry , physics , engineering
The presence of mobile colloids in subsurface environments can enhance subsurface contaminant migration by reducing retardation effects. We developed a mathematical model based on mass balance equations to describe the transport and fate of colloidal particles and a volatile contaminant in an unsaturated porous medium. When colloids are present in an unsaturated medium, the system representation include four phases: an aqueous phase, a carrier phase, a stationary solid matrix phase, and the air phase. Colloidal mass transfer between the aqueous and solid matrix phases and between the aqueous phase and the air‐water interface, and the contaminant mass transfer between aqueous and colloidal phases and between the aqueous phase and the air‐water interface are represented by kinetic expressions. Nondimensionalized governing equations are solved to analyze colloid and contaminant transport in an unsaturated column. A sensitivity analysis of the transport model was utilized to assess the effects of several parameters on model behavior. Results show that the effect of colloids on a volatile contaminant transport is highly dependent on the properties of the contaminant and the colloidal surfaces. The presence of an air‐water interface retards the volatile contaminant migration because of mass transfer rate across the air‐water interface, offsetting the facilitating effect of colloids. We tested the effects of varying Henry's constant and the contaminant mass transfer across the air‐water interface. The equilibrium assumption for the contaminant mass transfer across the air‐water interface may be valid for volatile contaminants with dimensionless Henry's constants less than one. As Henry's constant increases, the contaminant mass transferred across the air‐water interface is approximately 20% larger at 46% air saturation than at 15% air saturation because of a larger volume of air. At 15% air saturation, air phase contaminant reaches the equilibrium concentration at about 18 pore volumes with a large dimensionless Henry's constant ( H + =). However, at 46% air saturation, it takes over 20 pore volumes to reach the equilibrium concentration, even with a smaller Henry's constant ( H + quals;1).