Lumped Approach for Reactive Transport of Organic Compound Mixtures through Simulated Aquifer Sands in Lab-Scale Column Tests

Jin Chul Joo,Hee Sun Moon,Sun Woo Chang

doi:10.3390/w12113103

Abstract

The feasibility of the lumped approach for reactive transport of 12 organic compounds in mixtures through simulated aquifer sands with different organic carbon content (foc) within soil columns was evaluated. From direct measurements of effluent samples and temporal and spatial pore-water concentration profiles within soil columns, 12 organic compounds in mixtures were sorbed to different extents due to the different dependence of sorption on foc. Considering the tradeoff between accuracy and simplicity, four, five, and six pseudocompounds were determined for simulated aquifer sands with foc of 0.006%, 0.051%, and 0.221%, respectively, to approximate the reactive transport of 12 organic compounds in mixtures. Each pseudocompound presented obviously different reactive transport behavior in terms of both sorption capacity and nonlinearity, indicating that each pseudocompound contained components with relatively similar sorption capacities and nonlinearity. Similar to the results from batch equilibrium sorption tests, log Koc can be used as the a priori grouping criterion, although the relative contributions of different forces to the overall sorption may differ for different composition of organic mixtures and foc values of aquifer sands. Finally, the assignment of the Freundlich sorption parameters of pseudocompounds using averages of Freundlich sorption parameters of their components led to reasonable prediction for reactive transport of organic compounds in mixtures through the soil columns. Further study is warranted to evaluate the effective coupling between lumped approach and reactive transport model using complex multicomponent mixtures within heterogeneous subsurface systems.

Highlights

Most studies have involved individual systems to understand the reactive transport of each compound and to reconcile models for heterogeneous geosorbents, environmental contamination usually results in the presence of mixtures of compounds in the subsurface [1,2,3,4,5,6,7]
2–4, the organic compounds in mixtures were sorbed to different extents, and sorption to displayed in Figures 2–4, the organic compounds in mixtures were sorbed to different extents, and simulated aquifer sands generally decreased with the increase in polarity of organic compounds
Sorption to simulated aquifer sands generally decreased with the increase in polarity of organic relatively slow migration of migration nonpolarof organic compounds suggestssuggests that substantial amounts of

Summary

Introduction

Most studies have involved individual systems to understand the reactive transport of each compound and to reconcile models for heterogeneous geosorbents, environmental contamination usually results in the presence of mixtures of compounds (e.g., gasoline, fuel hydrocarbon/chlorinated solvents, pesticides, landfill leachates, and pharmaceuticals) in the subsurface [1,2,3,4,5,6,7]. The lumped approach has been used by (1) grouping the list of species by removing inessential components and/or lumping some species [1,3], (2) grouping the list of reactions by removing inessential side reactions and/or assuming quasi-equilibrium for some reaction steps [8], or (3) decomposing the kinetics into fast and slow parts and applying the quasi-steady-state-approximation to reduce its dimensionality [9] Such a lumped approach has been extensively applied in providing tractable approximations to the kinetics of complex hydrocarbon mixtures [9,10], in describing multicomponent sorption to simulated aquifer sands [1,3] and to humic substances [11], and in globalizing chemical lumping of species and reactions in wastewater treatment [12,13], secondary organic aerosol mixtures [14], toxicology of compound mixtures [15,16], and reactive transport of compound mixtures in the unsaturated zone [17]

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Conclusion