Impact of grain geometry on chlorohydrocarbon contaminant transformation and reductive dichlorination activity

Abstract

Porous media widely exists in natural aquifers, engineering materials (such as materials used to remove contaminants from water) and oil reservoirs, etc. Due to the complexity of particles contained in porous media, the fluid flow and contaminants transport are undoubtedly affected by the particle geometry of porous media. Two kinds of particle geometry models are developed to assess whether the geometry of grain plays an important role on chlorohydrocarbon contaminant transport and bioremediation. Porous medium properties such as tortuosity, permeability and entry pressure are quantified for the two kinds of particle geometries. Meanwhile, a laboratory experiment for perchloroethylene (PCE) transport is performed in a two-dimensional (2D) sandbox to verify permeability and entry pressure derived by different particle geometries. Comparison between geometry models and experimental results indicate rectangular particles (RP) with high μ (the ratio of width to length) and ellipse particles (EP) with low η (the ratio of semi-long axis to semi-shorter axis) agree well with the experiment. Moreover, the grains geometry that forms the porous matrix's solid domain applied in the experiment is also identified according to the numerical simulation of PCE migration. Furthermore, two kinds of particle geometries are coupled with UTCHEM, to derive the effects of particle geometry on Trichloroethylene (TCE) transport, redistribution and biodegradation by methanotrophs for a realistic three-dimensional (3D) aquifer application. Results suggest the geometry of grain has a significant influence on the properties of a porous medium. The remediation efficiency became higher when μ increased for RP and η decreased for EP. PCE infiltration rate was lowest for RP with high μ and EP with low η. Simulation results based on realistic groundwater bioremediation indicated RP with μ = 0.9, EP with η = 1.1 and EP with η = 1.3 achieved the highest bioremediation efficiency for TCE contamination.