Remediation of PAH-Contaminated Soils and Sediments: A ...

Ideal biodegradation of PAHs, where they are the sole bioavailable carbon
source, can be broken into three distinct phases based on diffusion of PAH into
the aqueous phase as shown in Figure 4 (Johnsen et al., 2005):
I. Exponential growth phase
II. Pseudo-linear growth as the dissolved PAH concentrations stabilize but
microbial biomass still increases linearly
III. Pseudo-stationary phase where biomass, PAH dissolution and
concentrations all stabilize
This ideal situation is somewhat complicated in soil because of adsorption of
PAH to organic matter and diffusion into small pores (both mechanisms of PAH
sequestration). It is suspected that microbial communities in soils remain in
Phase III (pseudo-stationary) as a result of the rate limiting diffusion of PAHs into
the aqueous phase (Johnsen et al., 2005). Transfer to the aqueous phase is
especially important for HMW hydrophobic compounds with low aqueous
solubility which tend to partition to the solid phase (especially organic matter) in
soils and sediments.
Figure 4. Schematic diagram for microbial biomass, specific microbial growth
rate, PAH dissolution rate and dissolved PAH concentration of bacterial batch
grown on solid PAHs (Johnsen et al., 2005).
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