Aerobic degradation of a toluene plume in homogeneous and heterogeneous porous media.

Degradation of aromatic hydrocarbons at the fringe of groundwater plumes is predominantly based on microbial transformations for which dispersive mixing at the pore-scale level constitutes the main driving force. The aim of the study was to compare the microbial degradation activity at the plume fringe in homogeneous and heterogeneous porous media. In two identical quasi two-dimensional flow-through microcosms, resembling a longitudinal section of an aquifer, a toluene plume was conveyed through (a) homogeneously distributed fine grained sediments and through (b) a heterogeneous set-up characterized by the inclusion of two subsequent rectangular high-conductivity (i.e. coarser grains) lenses. The experimental results showed that the contaminant removal by the aerobic toluene degrader Pseudomonas putida strain Fl was more effective in the heterogeneous system. The observed degradation enhancement was comprised in a range of 23-84%. Reactive transport modelling of the two-dimensional microcosm experiments showed that the governing processes of mixing of the reactants and kinetic degradation can explain the observed results well.