Influence of soil components on the transport of polycyclic aromatic hydrocarbon degrading bacteria through saturated porous media

The transport of a selected set of bacteria able to degrade polycyclic aromatic hydrocarbons (PAHs) was investigated in saturated column experiments, using as packing materials either a clay-containing soil or the isolated soil constituents montmorillonite clay, sand, or soil humic acid-clay complexes. The bacterial strains studied were able to grow on phenanthrene, anthracene, fluorene, fluoranthrene, and pyrene and were characterized for cell size, aspect ratio, hydrophobicity, and zeta potential. Removal of bacteria from the transport solution was quantified by calculating relative adhesion efficiencies (at) for all combinations of bacteria and packing materials. Transport through soil varied from strain to strain. However, no clear relationship was observed between the studied physicochemical characteristics of the bacteria and their transport. The relative differences between strains observed in soil were conserved in column experiments with isolated clay. Coating the clay surfaces with two different soil humic acid fractions drastically increased the transport of all bacteria tested. The nonionic surfactant Triton X-100 facilitated transport of hydrophobic cells at concentrations above its critical micelle concentration but had no effect on the transport of hydrophilic bacteria. We suggest that clay is the main retarding agent of PAH-degrading bacteria in soil.